Research ArticleHydrogen-Rich Syngas Production from Gasification andPyrolysis of Solar Dried Sewage Sludge Experimental andModeling Investigations

Ada Ben Hassen Trabelsi1 Amina Ghrib12 Kaouther Zaafouri3 Athar Friaa1

Aymen Ouerghi13 Slim Naoui1 and Habib Belayouni2

1Laboratory of Wind Energy Control and Waste Energy Recovery (LMEEVED) Research and Technology Centre of Energy (CRTEn)Borj-Cedria Technopark BP 95 2050 Hammam-Lif Tunisia2Department of Geology Faculty of Sciences of Tunis University of Tunis El Manar Tunis Tunisia3Laboratory of Microbial Ecology and Technology (LETMi) The National Institute of Applied Sciences and Technology (INSAT)Carthage University 2 Boulevard de la Terre BP 676 1080 Tunis Tunisia

Correspondence should be addressed to Aıda Ben Hassen Trabelsi aidabenhassenyahoofr

Received 8 May 2017 Revised 21 June 2017 Accepted 28 June 2017 Published 9 August 2017

Academic Editor Juan-Rodrigo Bastidas-Oyanedel

Copyright copy 2017 Aıda Ben Hassen Trabelsi et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Solar dried sewage sludge (SS) conversion by pyrolysis and gasification processes has been performed separately using twolaboratory-scale reactors a fixed-bed pyrolyzer and a downdraft gasifier to produce mainly hydrogen-rich syngas Prior to SSconversion solar drying has been conducted in order to reduce moisture content (up to 10) SS characterization reveals that thesebiosolids could be appropriate materials for gaseous products production The released gases from SS pyrolysis and gasificationpresent relatively high heating values (up to 996MJkg for pyrolysis and 802 996MJkg for gasification) due to their high contentsof H2 (up to 11 and 7wt resp) and CH4 (up to 17 and 5wt resp) The yields of combustible gases (H2 and CH4) show furtherincrease with pyrolysis Stoichiometric models of both pyrolysis and gasification reactions were determined based on the globalbiomass formula C120572H120573O120574N120575S120576 in order to assist in the products yields optimization

1 Introduction

In Tunisia since 1974 date of implementation of the firstwastewater treatment plant (WWTP) urban wastewatertreatment operations generate increasingly large quantitiesof sewage sludge (SS) According to the National Office forSanitation ldquoONASrdquo the generation of humid SS reachedabout 2 million tonsyear in 2009 and it was estimated at25 million tonsyear in 2016 Despite the large quantitiesof produced SS no specific handling procedure has beenadopted until now in Tunisia Actually the greater part ofgenerated SS (around 76) has always been stockpiled onWWTP (35) and on ONAS sites (41) and only 24was landfilled in municipal discharges to limit it negativeinfluence on environment In view of the current situation

of SS treatment in Tunisia and with the increasing awarenessregarding harmful characters of these wastes for environmentand human health valuable methods of SS managementare expected urgently Regarding the chemical compositionof urban SS which consists of heterogeneous mixture ofnontoxic organic matter and inorganic compounds [1] theenergetic valorization of these residues constitutes an alterna-tive way to convert such carbonaceous materials into highervalue-added products (biofuels heat and electricity) In thisregard to recover energy from SS various treatment options(anaerobic digestion incineration with energy recoverygasification and pyrolysis supercritical oxidation thermalhydrolysis etc) have been advanced by [2 3] In Tunisiathe anaerobic digestion is the most advanced practice forenergy recovery fromSS and it is already applied in practice in

HindawiBioMed Research InternationalVolume 2017 Article ID 7831470 14 pageshttpsdoiorg10115520177831470

2 BioMed Research International

some wastewater treatment plants such as Chotrana Station(around Tunis) However the thermochemical conversion ofSS especially via gasification and pyrolysis processes is stillundeveloped in Tunisia even at the RampD stage Thus inorder to advance the SS thermal processing field in Tunisiathe present work can be viewed as a feasibility assessment ofthese innovative applications (pyrolysis and gasification) toTunisian urban SS In fact these thermochemical processeshave been investigated in the literature for several biomassspecies and organic materials such as for Municipal SolidWastes ldquoMSWrdquo [4] plastic [5] waste tyres [6] paper [7]feathers wastes [8] and lignocellulosic residues [9 10]Concerning their application to SS some works have beenpublished in recent times The major parts of these worksfocused on the advance of new thermochemical technologiessuch as microwave assisted pyrolysis and catalytic pyrolysis[11 12] Other studies were centred on the possibility ofconverting SS into solid biochar valuable as fertilizers or asadsorbents via pyrolysis [13] but the produced sludge basedadsorbents did not yield high surface areas due to the highinorganic content of sludge [14] In order to improve thequality of the activated material for use as adsorbent [15]proposed two sequential steps of washing by using first asolution of HCl (in order to remove part of the ashes) andthen a solution of Na2CO3 (to extract most of the silicaremaining) The other parts focused on the production ofliquid biofuels (bio-oil) from SS [16 17] However the useof SS to produce gaseous products using thermochemicalprocesses has received little attention in the literature [18]

On behalf of these previous works a rigorous compar-ative study should be carried to evaluate the potential ofhydrogen-rich gas production from Tunisian SS using twodifferent thermochemical processes (pyrolysis and gasifica-tion) In the present work the production of solids oils andgas fromTunisian SS at high temperatures using pyrolysis wasexamined The results were compared with those obtainedwith gasification

It is important to distinguish pyrolysis from gasificationThe main difference between pyrolysis and gasification is theabsence of a gasifying agent in the case of pyrolysis Pyrolysisis a thermal degradation of organic compounds at a rangeof temperatures from 300 to 900∘C under oxygen-deficientcircumstances to produce various forms of products (a liquidfraction called bio-oil a solid fraction called biochar anda gaseous fraction called synthetic gas or syngas) whereasgasification is a thermal cracking of solid carbonaceousmaterial into a combustible gas mixture (syngas) mainlymade up of dihydrogen (H2) carbonmonoxide (CO) carbondioxide (CO2) and methane (CH4) and other gases withsome byproducts (solid char or slag oils and water) Theproduced syngasrsquo chemical composition and properties arelargely affected by the operational conditions throughoutpyrolysis and gasification (reactor temperature residencetime pressure gasifying agent nature and proportion etc)by the reactor geometry and by the feedstock characteris-tics (and mainly humidity) [7] The produced syngas frompyrolysis and gasification can be applied to run internalcombustion engines to generate electricity and as substitutefor fuel oils in direct heat application [19] to produce

chemicals in industries [20] and to power hydrogen fuelcells [21] Furthermore pyrolysis and gasification processeshave great flexibility in the choice of feedstocks but the majorconstraint of their application for SS conversion remains inthe high moisture content of these wastes (varying from afew percentages to more than 95 [3]) and the occurrence ofinorganic pollutants such as silicates aluminates and calciumand magnesium within SS The high moisture content ofSS can generate many problems related namely to energyconsumption of the pyrolysis reactor and to the productionof liquid fraction with high water content (and thus extra costfor purifying the products) In order to avoid such problemsin this study SS solar drying was performed in order to reacha humidity content around 10wt [22]

Since pyrolysis and gasification are complex chemicalmechanisms which incorporate several operational andenvironmental challenges of carbon-based feedstock manyresearchers have developed models of various types anddegrees of complexity in order tomake the comprehension ofphysical and chemical mechanisms inside the reactors easierand assist in the yield optimization Actually several modelshave been employed to simulate these thermochemical pro-cesses at different scales namely particle level multiphasereacting flow product distribution and reactor performanceand process integration and control For pyrolysis kineticmodels particle models and reactor models have beenproposed [23] and for gasification equilibrium modelscombined transport and kinetic models CFDmodels ANNsmodel and Aspen Plus models have been well discussed[22] Numerous software and numerical interfaces have beenemployed for mathematical modeling of thermochemicalprocesses for example gPROMS (Process Systems Enter-prise) ANSYS Fluent PHOENICS CFD2000 STATIS-TICA Neural Networks (SNN) (StatSoft) software AspenPlus and MATLAB [22]

The present work has been undertaken to investigatethe potential of gaseous biofuels production from TunisianSS through thermochemical processes and thus to examinethe main differences between the gasification and pyroly-sis reactions behaviours and products with special focuson the evolution of syngas composition liquid bio-oil ortars characteristics and solid residue properties The finalobjective of this study is to initiate the development of theSS thermochemical technologies for SS handling in Tunisiasince the use of this type of wastemay represent a valid energysource

2 Materials and Methods

21 Materials Thedewatered SS samples were collected fromldquoRades Central Wastewater Treatment Plantrdquo near Tunis(Tunisia) and then predried in a solar dryer installed inthe Research and Technology Centre of Energy (CRTEnTunisia) for one week until a water content around 10 sincemost of the previous studies on SS pyrolysis were appliedon SS with humidity between 5 and 35 [22] The solardried samples rounded aggregates with particle size between05mm and 2 cm in diameter were collected in glass bottles

BioMed Research International 3

for analysis and for pyrolysis and gasification experimentsThe solar driedmaterials have been characterized by ultimateanalysis (CHNS-O) and proximate analyses (moisture ashcontent volatile matter content and fixed carbon) followingstandardized procedures The CHN elemental compositionwas determined using Perkin Elmer 2400 CHN elementalanalyzer while the sulphur content was determined viaHORIBA Jobin Yvon elemental sulphur analyzer [24] SSHigher Heating Value (HHV) was calculated using thefollowing formula [25]

HHV = 03491C + 11783H + 01005S minus 01034O

minus 00151N minus 00211AMJkg(1)

The moisture content was determined by measuring theweight loss after drying the studied samples at 105∘C for 24 h[26] The ash content was determined by dry combustion ina muffle furnace at 550∘C for 3 h [26] The volatile matter(VM) contents were determined based on the mass loss aftercombustion of the samples at 900∘C for 4min [26] The fixedcarbon (FC) contents were calculated using the differencebetween the dry matter and the sum of the ash contentsplus the VM contents The fixed carbon (FC) content wascalculated in the following equation

FC = DM minus (VM + Ash) (2)

The hydrogen index (expressed in mg hydrocarbonsg TotalOrganic Carbon mg HCg TOC) of predried SS wasdetermined by Rock-Eval pyrolysis using a model VIdevice (Vinci Technologies) Predried SS samples were firstpyrolyzed under N2 up to 650

∘C and the amounts of gaseousproducts (hydrocarbons CO2 and CO) were continuouslymeasured via flame-ionization (FI) and infrared detectionThe TOC is determined as the sum of pyrolyzed organic car-bon and residual organic carbon the latter being determinedby combustion after the pyrolysis phase

FTIR spectroscopic analyses were performed usinga Perkin Elmer Spectrum BX spectrophotometer inabsorbance mode between 4000 and 400 cmminus1 onpellets made from a mixture of predried SSKBr The fun-ctional groups contained in studied sample were determinedbased on the identification of FTIR spectra according topreviously published data [1 12 16] The thermogravimetricmeasurements were performed using a ldquoSETSYSrdquo (SetaramInstrumentation) thermobalance The experimental con-ditions were as follows inert atmosphere (He) temperaturerange between 20 and 1400∘C heating rate about 20∘Cminand sample mass around 20mg

22 Pyrolysis and Gasification Procedures The pyrolysis andgasification experimentsrsquo main conditions are reported inTable 1

221 Pyrolysis Experimental Setup The pyrolysis unit (Fig-ure 1(a)) is a fixed-bed reactor (stainless steel made 30 cmheight and 15 cm internal Oslash) where the SS sample isplaced in batch and then heated until the final pyrolysistemperature with an electric furnace At the top of the

Table 1 Pyrolysis and gasification processes conditions

Pyrolysis GasificationRaw material Predried SS Predried SSCarrier gas Nitrogen AirReaction temperature (∘C) 500-550-600 gt900Heating rate (∘Cminminus1) 10-15-20 mdashCondensation temperature (∘C) minus5 minus5Reaction time (min) sim50 sim160

reactor there is (i) a nitrogen injection system to preventoxygen introduction into the reactor and to guarantee aninert medium for pyrolysis reactions and (ii) a thermocoupleK-type immersed inside the reactor to control the internalaxial temperature The pyrolysis vapors leave the top of thereactor and go on to the condensation system which consistsof two condensers where a part of bio-oil is condensed andstored in a conical flask The condensation system operateswith continuous cold glycolated water (minus5∘C) circulationPyrolysis liquid products consisted of two phases aqueousphase and organic phase which are easily separated usingdecantation (Figure in Supplementary Material availableonline at httpsdoiorg10115520177831470) The noncon-densable gases enter into a purification system constituted ofmany filters in series (i) a bubbling system using distilledwater to remove remaining hydrocarbons and water withinnoncondensable gases (ii) an activated carbon column forretention of small particles and (iii) low pressure gas filters toenhance the particulates andmoisture removalThe chemicalcomposition of cleaned gases is then determined using anon-line gas analyzer The carbonaceous residue is collectedin the bottom of the reactor The pyrolysis experiments wererepeated three times and the products yields presented arethe mean value of three equivalent experiments The severalyields of pyrolysis products are calculated as indicated in [27]

222 Gasification Experimental Setup The gasification unit(Figure 1(b)) consists of a 50 kWth downdraft fixed-bedreactor type ldquoImbertrdquo (stainless steel made circular in crosssection with 80 cm internal diameter and 120 cm height)The feeding capacity ranges from 2 to 8 kgh The SS sampleis placed in batch in the reactor and the gasifying agent(air) is introduced continuously at the bottom part of thereactor with a steady flow rate Axial temperature evolu-tion is detected using a series of K-type thermocouples (8thermocouples) and recorded automatically every 10 s bya controller computer The produced gases pass througha quenching system for tar removal The noncondensablegas mixture is then purified using the same gas cleaningsystem (water bubbler moisture absorber and low pressurefilters) used for pyrolysis gases and described below Thechemical composition of cleaned gases is then determinedusing an on-line gas analyzer The remaining solid residuecontaining inorganic components ashes and unconvertedcarbon is collected in the bottompart of the reactor after eachexperiment

BioMed Research International 3

for analysis and for pyrolysis and gasification experimentsThe solar driedmaterials have been characterized by ultimateanalysis (CHNS-O) and proximate analyses (moisture ashcontent volatile matter content and fixed carbon) followingstandardized procedures The CHN elemental compositionwas determined using Perkin Elmer 2400 CHN elementalanalyzer while the sulphur content was determined viaHORIBA Jobin Yvon elemental sulphur analyzer [24] SSHigher Heating Value (HHV) was calculated using thefollowing formula [25]

HHV = 03491C + 11783H + 01005S minus 01034O

minus 00151N minus 00211AMJkg(1)

The moisture content was determined by measuring theweight loss after drying the studied samples at 105∘C for 24 h[26] The ash content was determined by dry combustion ina muffle furnace at 550∘C for 3 h [26] The volatile matter(VM) contents were determined based on the mass loss aftercombustion of the samples at 900∘C for 4min [26] The fixedcarbon (FC) contents were calculated using the differencebetween the dry matter and the sum of the ash contentsplus the VM contents The fixed carbon (FC) content wascalculated in the following equation

FC = DM minus (VM + Ash) (2)

The hydrogen index (expressed in mg hydrocarbonsg TotalOrganic Carbon mg HCg TOC) of predried SS wasdetermined by Rock-Eval pyrolysis using a model VIdevice (Vinci Technologies) Predried SS samples were firstpyrolyzed under N2 up to 650

∘C and the amounts of gaseousproducts (hydrocarbons CO2 and CO) were continuouslymeasured via flame-ionization (FI) and infrared detectionThe TOC is determined as the sum of pyrolyzed organic car-bon and residual organic carbon the latter being determinedby combustion after the pyrolysis phase

FTIR spectroscopic analyses were performed usinga Perkin Elmer Spectrum BX spectrophotometer inabsorbance mode between 4000 and 400 cmminus1 onpellets made from a mixture of predried SSKBr The fun-ctional groups contained in studied sample were determinedbased on the identification of FTIR spectra according topreviously published data [1 12 16] The thermogravimetricmeasurements were performed using a ldquoSETSYSrdquo (SetaramInstrumentation) thermobalance The experimental con-ditions were as follows inert atmosphere (He) temperaturerange between 20 and 1400∘C heating rate about 20∘Cminand sample mass around 20mg

22 Pyrolysis and Gasification Procedures The pyrolysis andgasification experimentsrsquo main conditions are reported inTable 1

221 Pyrolysis Experimental Setup The pyrolysis unit (Fig-ure 1(a)) is a fixed-bed reactor (stainless steel made 30 cmheight and 15 cm internal Oslash) where the SS sample isplaced in batch and then heated until the final pyrolysistemperature with an electric furnace At the top of the

Table 1 Pyrolysis and gasification processes conditions

Pyrolysis GasificationRaw material Predried SS Predried SSCarrier gas Nitrogen AirReaction temperature (∘C) 500-550-600 gt900Heating rate (∘Cminminus1) 10-15-20 mdashCondensation temperature (∘C) minus5 minus5Reaction time (min) sim50 sim160

reactor there is (i) a nitrogen injection system to preventoxygen introduction into the reactor and to guarantee aninert medium for pyrolysis reactions and (ii) a thermocoupleK-type immersed inside the reactor to control the internalaxial temperature The pyrolysis vapors leave the top of thereactor and go on to the condensation system which consistsof two condensers where a part of bio-oil is condensed andstored in a conical flask The condensation system operateswith continuous cold glycolated water (minus5∘C) circulationPyrolysis liquid products consisted of two phases aqueousphase and organic phase which are easily separated usingdecantation (Figure in Supplementary Material availableonline at httpsdoiorg10115520177831470) The noncon-densable gases enter into a purification system constituted ofmany filters in series (i) a bubbling system using distilledwater to remove remaining hydrocarbons and water withinnoncondensable gases (ii) an activated carbon column forretention of small particles and (iii) low pressure gas filters toenhance the particulates andmoisture removalThe chemicalcomposition of cleaned gases is then determined using anon-line gas analyzer The carbonaceous residue is collectedin the bottom of the reactor The pyrolysis experiments wererepeated three times and the products yields presented arethe mean value of three equivalent experiments The severalyields of pyrolysis products are calculated as indicated in [27]

222 Gasification Experimental Setup The gasification unit(Figure 1(b)) consists of a 50 kWth downdraft fixed-bedreactor type ldquoImbertrdquo (stainless steel made circular in crosssection with 80 cm internal diameter and 120 cm height)The feeding capacity ranges from 2 to 8 kgh The SS sampleis placed in batch in the reactor and the gasifying agent(air) is introduced continuously at the bottom part of thereactor with a steady flow rate Axial temperature evolu-tion is detected using a series of K-type thermocouples (8thermocouples) and recorded automatically every 10 s bya controller computer The produced gases pass througha quenching system for tar removal The noncondensablegas mixture is then purified using the same gas cleaningsystem (water bubbler moisture absorber and low pressurefilters) used for pyrolysis gases and described below Thechemical composition of cleaned gases is then determinedusing an on-line gas analyzer The remaining solid residuecontaining inorganic components ashes and unconvertedcarbon is collected in the bottompart of the reactor after eachexperiment

4 BioMed Research International

(1)

C

B

(2)

(3)

(5)

(4)

(11)

(10)

(13)(14)

(15)

(16)

(9)

(6)

(8)(8)

(17)

(7)(12)

2

(a)

C

B(1)

(2)

(2)

(2)

(17)

(18)

(15)(16)(3)

(6)

(5)

(8)

(9)

(10)

(2)

(11)

(12)

(13)(19)

(4)

(7)

(14)

(b)

Figure 1 Schematics of systems used in SS pyrolysis (a) and gasification (b) experiments (a) Pyrolysis system (1)N2 gas cylinder (2) heatingcontrol panel (3) control transfer (4) N2 inlet (5) thermocouple (6) sewage sludge (7) pyrolysis reactor (8) electrical furnace (9) vaporsoutlet (10) condensation system (11) liquid fraction (12) noncondensable gases (13) gas purification system (14) activated carbon column(15) gas filters (16) gas analyzer (17) laptop for data acquisition (b) Gasification system (1) gasification reactor (2) sewage sludge (3) flameintroduction (4) gas cylinder (5) thermocouples (6) oxidizing agent (air) introduction (7) air compressor (8) temperature recorder (9)laptop for temperature acquisition (10) ash collector (11) syngas outlet (12) condensation system (13) tars (14) noncondensable gases (15)gas purification system (16) activated carbon column (17) gas filters (18) gas analyzer (19) laptop for data acquisition

23 Pyrolysis andGasification Products Characterization Thechemical composition of syngas flowing out from the pyroly-sis and gasification reactors separately was determined usingan on-line analyzer (GEIT 3160 model) equipped with (i)an Infrared detector (for analyzing CO CO2 CH4 and lighthydrocarbons (C119899H119898)) (ii) aThermal Conductivity Detector(TCD) to quantify H2 and (iii) an electrochemical cell for O2measurementThe syngas heating value is also determined bythe same analyzer

The elemental composition CHN of bio-oil released frompredried SS pyrolysis was determined in the same conditionsas raw materials The fuel properties of bio-oil obtained from

SS pyrolysis were measured according to the internationalstandards used for petroleum products (density viscosityand water content [28]) FTIR spectroscopy was applied tobio-oil and biochar obtained from the pyrolysis of SS andto the condensable tars and solid residue obtained from thegasification of SS in the same conditions as raw materials

24 Mathematical Modeling StoichiometricModel Establishment

241 Raw Material Mole Numbers According to Redfieldformula reported in his study [29] in marine biology to

BioMed Research International 5

determinate the composition of phytoplankton the ratio ofthe elements does not change The number of carbons 120572 (inthis case 106 according to Redfield formula) is determined inorder to calculate mole number of other elements

Let 1198881 and 1198882 be the following coefficients 1198881 = C12 and1198882 = 1205721198881

The formula of the compound is as follows C120572H120573O120574N120575S120576with

120573 =H lowast 11988821

120574 =O lowast 119888216

120575 =N lowast 119888214

120576 =S lowast 1198882321

(3)

Themass of the compound is1198980 = 12120572+120573+16120574+14120575+321120576(in g)

Let 119898119894 be the initial mass of the compound let 119901119894 be theproportion of the organic element 119894 and let119872119894 be its molarweightThe number of moles of the species 119894 into the biomassis 119899119895 = (119898119894 lowast 119901119895)119872119895 (in mol)

242 Products Yields For determined temperature and heat-ing rate the mass yields are named 119877119887 119877119888 and 119877119892 respec-tively for bio-oil biochar and syngas Let 1198980 be the initialquantity of biomass (in g) 119898119887 119898119888 and 119898119892 are respectivelythe masses of bio-oil biochar and syngas The mass of theproduct p is119898119901 = (119877119901100) lowast 1198980 (in g)

243 SyngasMole Numbers Theproduct gases are CO CO2O2 H2 CH4 C119899H119898 and N2 Let 119891119894 be the fraction of thegas 119894 let119872119894 be its molar mass and let 119898119892 be the mass of theproduct gas The mole number of the gas 119899119894 is calculated bythe following equation 119899119894 = (119898119892 lowast 119891119894)119872119894 (in mol)

For the gasification the masses of produced gases arecalculated as follows119898119892 = 1198980 lowast (1 minus (119890 + 119888)100) (in g) with 119890 being the water

content of the biomass 119888 being the ash content and1198980 beingthe initial mass

244 BiocharMoles Numbers Let119901119895 be the proportion of theorganic element 119895 and let119872119895 be its molar mass The numberofmoles of the species 119895 in the biochar 119899119895 is 119899119895 = (119898119888lowast119901119895)119872119895(in mol)

245 Organic Matter Balance As hypothesized N2 is con-sidered as inert element in pyrolysis and will not be countedin the balance of organic matter

3 Results and Discussion

31 Feed Materials Characteristics

311 Elemental Composition The elemental chemical com-position the physicochemical properties the HHV value

and the Rock-Eval parameters of the predried SS sample areshown in Table 2 The carbon and hydrogen contents arerelatively high (roughly 48wt and 8wt resp) and compa-rable to those of other SS used in pyrolysis and advanced by[16 18 30] and to some lignocellulosicmaterials [9] (Table 2)The nitrogen and sulphur contents are respectively about171 wt and 096wt these contents are lower than thoseobtained for other SS samples (from 4 to 8 for nitrogenand from 06 to 76 wt for sulphur Table 2) The highnitrogen content observed in studied SS is attributed to theprotein fraction contained in microorganisms used for waterpurification through biological degradation [31] The oxygencontent is around 10 and it is significantly lower than thoseof lignocellulosic residues and SS samples (approximatelybetween 188 and 537 Table 2)

These differences in elemental composition between SSsamples cited in previous studies and those of this work couldbe explained by the difference in the origin and the treatmentsin wastewater plant [31]

Proximate analysis (Table 2) showed that SS moisturecontent is about 949 and this low humidity was reachedusing a solar drying technologyThe purpose of the SS dryingwas to achieve water content less than 10 since most ofthe previous studies on SS pyrolysis and gasification wereapplied for raw materials with humidity between 5 and 35[1 16 18 22] in order to reduce the occurrence of steamreforming reactions at high temperatures and to increase theproduction of hydrogen-rich gasThe amounts of ash andVMin SS are quite high (around 3080 and 5881 resp) andthey are in the same range of SS used in previous pyrolysisstudies and reported by other researchers [1 18 22 31]

The Rock-Eval hydrogen index (HI) is around 476mgof hydrocarbons by g of Total Organic Carbon (mg HCgTOC) indicating a high potential of hydrogen productionfor the predried SS In fact measured usually for evaluatingthe source rock maturity in petroleum prospection the HIparameter indicates the richness of studied SS in hydrogenwhich can be converted into gaseous hydrogenated compo-nents via pyrolysis For the studied samples the HI valueis very high confirming them to be appropriate substratesfor the production of hydrogen-rich synthesis gas suchas H2 CH4 and C119899H119898 SS calorific value is quite high(around 25MJkg) compared to those of other SS used forpyrolysis experiments (around 17MJkg [18] and between 9and 12MJkg [1 16])

312 FTIR Functional Groups Composition Figure 2(a)shows the IR spectrum obtained from predried SS The SSFTIR spectrum contains a large band between 3200 and3600 cmminus1 attributed to OndashH stretching vibration of car-boxylic and alcoholic groups The presence of the absorptionpeaks between 2800 and 3000 cmminus1 and around 1400 cmminus1indicates the high content of aliphatic functions originatedmainly from lipid fraction contained in SS The richnessof aromatic groups is revealed by the large band at around1640 cmminus1 related to C=C and other little peaks around700ndash900 cmminus1 attributed to CndashH in aromatic structures Theabundance of O-containing groups is observed essentially by

6 BioMed Research International

Table 2 Characteristics of studied solar dried SS and others used in thermochemical conversion studies according to literature

Ultimate analysis ()Studied solar dried SS Thipkhunthod et al 2007 Tsai et al 2009 Fonts et al 2012 Chen et al 2015

Sewage sludge Lignocellulosic biomassC 4821 plusmn 1 276ndash484 316ndash423 231ndash399 421ndash493H 817 plusmn 03 65ndash74 49ndash63 38ndash59 55ndash61O 1015 353ndash537 318ndash356 188ndash235 442ndash509N 171 plusmn 01 39ndash74 55ndash77 25ndash79 00ndash09S 096 plusmn 01 12ndash76 06ndash14 08ndash10 01ndash08

Proximate analysis ()Moisture content 949 plusmn 03 32ndash76 160ndash180 15ndash71 36ndash103Ash content 3080 plusmn 2 434ndash714 242ndash449 226ndash520 05ndash79Volatile matter 5881 plusmn 3 259ndash524 390ndash548 383ndash668 718ndash832Fixed carbon 090 27ndash64 mdash 08ndash197 57ndash174Hydrogen indexlowast 476 mdash mdash mdash mdashHHV (MJkg) 2482 mdash mdash mdash mdashlowast in mg hydrocarbong organic carbon

4000

3600

3200

2800

2400

2000

1800

1600

1400

1200

1000 80

0

600

400

minus0059minus004minus002minus000

002004006A008010012014016

0183ndashOHndashNH

C=C

ndashCH

ndashCH

CndashH

(cＧminus1)

(a)

50 100

150

200

250

300

350

400

450

500

550

600

650

700

TG (m

g)

minus10

minus8

minus6

minus4

minus2

0

Hea

t flow

(V

)

minus4minus3minus2minus1012345

dTG

(mg

min

)minus040minus035minus030minus025minus020minus015minus010minus005

000

Exo

Sample temperature (∘C)

(b)

Figure 2 FTIR spectrum (a) and TGADTA diagrams (b) for solar dried SS sample

the presence of the large absorption band around 1037 cmminus1assigned to CndashO stretching of carbohydrates and alcoholfunctions and reflecting the concurrence of exopolysaccha-rides released by microorganisms of predried SS andorfrom wastewater itself The FTIR spectroscopy structuralcharacterization of the predried SS reveals the high organiccharacter of theses wastes and mainly the oxygenated andaromatic functional groupsrsquo richness It may be concludedthat these wastes are suitable feedstock for biofuels produc-tion through pyrolysis and gasification processes

313 Thermogravimetric Behaviour The results of the ther-mogravimetric (TG) and differential thermal (DT) analysesof predried SS are given in Figure 2(b) The TG curve ispresented in green color indicating the variation of the massloss (expressed in mg) of studied SS under heating whereasthe curve in red color (dTG) shows the evolution of the mass

loss rate (expressed in mgmin) The blue curve indicatesthe heat flow (expressed in 120583V) used during experimentsThe thermogravimetric analysis was applied in this studyto have prior knowledge of initial and final temperaturesfor thermal degradation of SS As can be observed fromFigure 2(b) the predried SS thermal decomposition and thusthe loss of mass took place in two big steps the initial weightloss occurring between 50∘C and 100∘C and related to adrying phase (loss of physically absorbed water molecules) Itcorresponds to amass loss around 464 of the originalmassA second strong weight loss (around 4643 of its originalmass) occurs between 200∘C and 600∘C with a large peakcentred at 337∘C and a shoulder between 220 and 320∘CThisstep corresponds mainly to the volatilization of volatiles inSS and thus to the degradation of main organic componentscontained in SS In reality various organic compoundsdecompose between 200 and 400∘C hemicelluloses cellulose

BioMed Research International 7

536

1311

8153

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Prod

ucts

yiel

ds (w

t)

TarsSolid residueSyngas

(a)

4030 39583095

3958

46934967

20121350

1938

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

10 15 20

Prod

ucts

yiel

ds (w

t)

Bio-oilBiocharSyngas

Heating rate (∘Cmin)

(b)

2739

4030

48465009 4809

2977

2247

1161

2177

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

500 550 600

Prod

ucts

yiel

ds (w

t)

Pyrolysis temperature (∘C)

Bio-oilBiocharSyngas

(c)

Figure 3 SS pyrolysis products distribution (a) variable pyrolysis temperature and invariable heating rate 15∘Cmin (b) variable heatingrate and invariable temperature 550∘C (c) SS gasification products distribution

and lignins leather some N-containing compounds such asaliphatic amino acids and aromatic compounds contained inplastic materials But due to the great heterogeneity of thestudied SS chemical composition it is difficult to attributethis decomposition to specific organic compounds After600∘C SS sample showed a weight loss of 316 of its originalmass attributed mainly to the decomposition of inorganicmaterials

32 Pyrolysis and Gasification Products Distribution Pyrol-ysis experimental conditions influence the products distri-bution and properties Among these parameters pyrolysisfinal temperature has the largest effect on the products yieldsThe pyrolysis temperature has been evaluated based on thethermogravimetric results and the previous studies of SSpyrolysis found in the literature Figure 3(a) exhibits theproducts (bio-oil biochar and syngas) distribution of SS

8 BioMed Research International

pyrolysis at different final temperatures (500 550 and 600∘C)and at an invariable heating rate (15∘Cmin) and a constantcooling temperature (minus5∘C) As it can be seen an increasein pyrolysis temperature (from 500 to 600∘C) results in adecrease in biochar yield (from 50 to 30) and an increasein liquid fraction yield (from 27 to 48) due probably to thepromotion of devolatilization reactions At higher tempera-tures secondary reactions involving volatiles such as thermalcracking are improved leading to a reduction in the liquidyield and an increase in the gas yieldThe decrease in biocharyield is possibly related also to further pyrolysis conversionand thus to a greater primary decomposition of the initialfeedstock or to secondary reactions of the solid residue [13]The syngas yield is variable in all conditions the pyrolysisgas amount is not very high (does not exceed 23) andthe optimum pyrolysis temperature obtained for maximumsyngas production is around 500∘CBy investigating the effectof reaction temperature (in the range of 450ndash600∘C) on theyields of SS pyrolysis products [1] obtained a maximum gasyield of 20 in dry and ash-free basis at 600∘C whereas [32]reported a maximum yield of gaseous products in the rangeof 15ndash25 at high temperature (700∘C) Reference [17] bystudying the influence of pyrolysis temperature on productsdistribution reported that gas yield remains almost constant(around 20ndash22) as the pyrolysis temperature increased from350 to 550∘C but above 550∘C a significant increase in gasproduction is observed (reaching a gas yield around 32)

Apart from temperature heating rate also plays a signif-icant role in products yields variation during SS pyrolysisFigure 3(b) shows the influence of heating rate variation onproducts yields distribution at an invariable final temperature(550∘C) and a constant cooling temperature (minus5∘C) It can beseen that an increase in the heating rate leads to a decreasein the liquid fraction and to an increase in the solid fractionwhile the gas fraction yield remains variableThese results arein agreement with the literature Reference [33] using twoheating rates (5∘Cmin and 60∘Cmin) demonstrated that theincrease in heating rate gives an increase in liquid productsyield and a decrease in biochar yield

Regarding the gasification process some operationalproblems were encountered in the measurement of productsyields such as (i) tars condensation and deposits duringcooling of the gasifier and at the outlet of the reactor and(ii) presence of tars in the produced syngas Roughly theobtained yields given in Figure 3(c) are as follows 82 ofsyngas 13 of solid residue and 5 of tars

33 Gasification Reactor Temperature Distribution In orderto distinguish the different zones within the gasificationreactor the temperature data recorded inside the gasifierwereexploited Figure 4 shows the inside reactor axial temperatureevolution obtained during the predried SS gasification expe-riences using five active thermocouples (from T1 to T5) Thetemperature curves recorded by thermocouples T1 (orangecolor) and T2 (green color) show a regular temperaturevariation around 50∘C until 100min from the beginningof the gasification experiment After that the temperatureincreased slowly for T1 and suddenly for T2 to reach 240∘Cand 290∘C respectively which were maintained until the

0

100

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000Time (sec)

T1 (∘C)

T2 (∘C)

T3 (∘C)

T4 (∘C)

T5 (∘C)

Tem

pera

ture

(∘C)

Figure 4 Reactor axial temperature evolution during solar dried SSgasification process

end of the experiment This corresponds to the drying zonein the reactor In this drying zone moisture content of thebiomass is reduced considerably The temperature variationsrecorded by thermocouples T3 (pink color) and T4 (bluecolor) show a regular evolution from room temperature toa maximum of 520∘C and by the end of the experimentto 750∘C as maximum temperature indicating the pyrolysisphase In this pyrolysis stage the thermal cracking of biomassoccurs in the absence of oxygen and solid residue (charcoal)and volatile vapors (containing carbon monoxide hydrogencarbon dioxide and hydrocarbon gases) are released [22]Thermocouple T5 (black color) recorded temperatures inthe gasification zone as it reaches rapidly high temperatureabove 900∘CThe gasification process of predried SS samplesstarted at moderate temperatures (between 600 and 700∘C)and achieves high temperatures (above 900∘C) at the end ofthe gasification experiment In this reduction area severalreactions occur and the temperature ranges between 800 and1000∘C These reactions are mostly endothermic in natureThe distribution of the gasifier axial temperature enables usto follow different mechanisms occurring throughout thegasification process and thus to delineate the different zoneswithin the reactor such us drying pyrolysis combustion andgasification Furthermore the temperature evolution showsthat the predried SS gasification reactions take place at hightemperature (above 900∘C) In this gasification area severalreduction reactions occur The main reactions in this zone asdescribed by [22] are as follows

Water-Gas Reaction

C +H2O 997888rarr CO +H2 Δ119867 = 1314 kJmol (4)

BioMed Research International 9

0

2

4

6

8

10

12

0102030405060708090

100

300 350 400 450 500 550 600 550 500 450 400 350 300

Calc

ulat

ed L

HV

(MJk

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2

（4

n（m

（2

2

(a)

0123456789

0102030405060708090

100

300 400 500 600 700 800 900 800 700 600 500

Calc

ulat

ed L

HV

(MJK

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2 2

（4

n（m

（2

2

(b)

Figure 5 Syngas chemical composition and LHV evolution during (a) SS pyrolysis process (600∘C and 20∘Cminminus1) and (b) SS gasificationprocess

Boudouard Reaction

C + CO2 997888rarr 2CO Δ119867 = 1726 kJmol (5)

Shift Reaction

CO2 +H2 997888rarr CO +H2O Δ119867 = 42 kJmol (6)

Methane Reaction

C + 2H2 997888rarr CH4 Δ119867 = 75 kJmol (7)

In total the fixed-bed downdraft gasifier is recommendedequipment to study the gasification reactions and mecha-nisms at laboratory scale and to produce clean gas but themain disadvantages of this type of gasifier are its low ther-mal efficiency and the great difficulties related to handlingbiomass with high moisture and ash contents [22]

34 Pyrolysis and Gasification Products Characterization

341 Syngas Composition

(1) Pyrolysis Syngas Composition The syngas chemical com-position obtained throughout SS pyrolysis is shown in Fig-ure 5(a) The major gaseous products obtained from SSpyrolysis are CH4 (up to 1762) CO2 (up to 1203)H2 (up to 1085) CO (up to 726) and C119899H119898 (up to430) From Figure 5(a) it could be roughly seen that thevariation of several produced gases is almost constant witha high release at the beginning of the experiment (from300∘C) to achieve maximum of combustible gas productionat 600∘C and finally a gradual decrease marking the end ofthe pyrolysis reactions Among combustible gases CH4 andH2 are found to be the most abundant compounds of the

produced gases from SS pyrolysis The H2 high content inthe syngas mixture produced by pyrolysis could be explainedby the catalytic effect of the minerals contained in studiedSS (ash content around 3080) This catalytic effect in SSpyrolysis was highlighted by many authors [12 16] whostudied the correlation between the H2 percentage producedby pyrolysis of SS and the SS ash content and demonstratedthat the catalytic effect of the ash in the dehydrogenationreactions enhances the H2 production whereas the highH2 production is often correlated directly to the high ashcontent of SS which have a catalytic effect during thermalcracking and mainly in the dehydrogenation reactions [1216] Moreover the formation of CO and CO2 could beattributed to the decomposition of oxygenated groups suchas decarboxylation and decarbonylation [32] Other worksthat were conducted on SS pyrolysis have reported similar gascompositions Reference [12] presented a syngas compositionproduced from SS pyrolysis with a high yield (between 45and 66) of CO and H2 and reported that the gas fromthe conventional oven is much richer in hydrocarbons (25)than that from themicrowave ovens (6ndash11) According to [1]that studied SS flash pyrolysis in a conical spouted bed reactorat 600∘C the gas mixture composition is as follows 35 ofCO2 23 of CO 23 of H2 and 24 of C1ndashC4 Reference[16] obtained with the pyrolysis of three SS samples a gasmixture containing up to 60 of CO2 34 of CO 28 ofH2 11 of CH4 and 2-3 of C119899H119898

The calorific value (LHV) of the produced gas mixtureobtained under the pyrolysis conditions used in the presentstudy reaches a maximum of 996MJkg indicating a highcontent of combustible gases in this gaseous mixture Thisrelatively elevated heating value of the gas mixture can bevalorized as an alternative source of heating for the pyrolysisreactor The obtained heating values of gases are in the samerange as those reported by previous studies In fact the

10 BioMed Research International

heating values of gases from conventional pyrolysis were130ndash140MJm3 whereas with the microwave method theheating values ranged from 66 to 86MJm3 [11] Reference[33] that studied the pyrolysis of SS reported that the releasedgases have a maximum heating value around 25MJm3

(2) Gasification Syngas Composition The syngas chemicalcomposition analysis throughout the gasification experiment(Figure 5(b)) reveals that the obtained syngas is a mixtureof the following main components CO2 (up to 1843) CO(up to 76) H2 (up to 732) CH4 (up to 536) andC119899H119898 (up to 236) As can be observed in Figure 5(b)when the reactor temperature increased the CO and CO2concentrations increased due to decarbonylation and decar-boxylation reactions at high temperatures H2 concentrationincreased also with the temperature increase with a max-imum around 732wt at nearly 900∘C and this is due tonot only the cracking reactions but also dehydrogenationreactions promoted by the catalytic effect of the inorganicfraction [1 16] CH4 and C119899H119898 showed the same trendwith a slight variation from the beginning These drawndata are in agreement with those described by [2] where atypical gasification gaseousmixture is characterized by a highhydrogen content (H2 889ndash1117 vol) It contains also othercombustible compounds including CO (628ndash1077 vol)CH4 (126ndash209 vol) carbon dioxide and some light hydro-carbons Similar observations have been advanced by [17] thatstudied SS gasification using downdraft reactor and indicatedthat produced syngas is composed mainly of combustiblegases such as H2 (880ndash1115 vol) CO (631ndash1063 vol)CH4 (125ndash207 vol) and C119899H119898 (076ndash110 vol) and non-combustible gases such as N2 and CO2

The heating value of the syngas obtained under thegasification conditions used in the present study reachesa maximum of 802MJkg This calorific value is higherthan those reported for SS pyrolysis Reference [18] reportedgross heating values ranging from 487 to 555MJkg forsyngas produced from SS gasification in a downdraft gasifierwhereas [34] advanced LHV values ranging between 415 and709MJkg for syngas produced from two types of SS

342 Bio-Oil and Biochar Properties The bio-oil elementalcomposition is as follows C 5659wt H 824wt N396wt S 032 wt and O 3089wt The obtained car-bon hydrogen and sulphur contents are lower than thosefound by other authors from pyrolysis of SS Thus [34]obtained for bio-oils produced from conventional pyrolysisof SS carbon content between 709 and 845 wt hydrogencontent between 103 and 124 wt and sulphur contentbetween 02 and 06 wt Reference [33] reported for organicfraction of SS pyrolysis liquids between 494 and 626wtfor carbon and between 98 wt and 115 wt for hydrogennitrogen and sulphur contents are almost invariable [33 35]The knowledge of elemental composition (mainly carbonhydrogen and sulphur contents) is necessary for potentialutilization of these bio-oils as biofuels or for further process-ing to petrochemicals or biodiesel

The bio-oil density at 15∘C kinematic viscosity and watercontents of both organic and aqueous fractions from SS

Table 3 Fuel properties of liquid fractions obtained from SSpyrolysis (at 550∘C and 15∘Cmin)

Density (15∘C)(KgL)

Viscosity(40∘C)(mm2s)

Water content()

Organic fraction 09743 63 16Aqueousfraction 1 106 25

pyrolysis are reported in Table 3The organic fraction densityaround 09743Kgm3 is quite higher than those required bythe Tunisian standard fuels (between 820 and 860 kgm3)and also higher than those of similar bio-oils obtained fromdifferent feedstocks [27] The organic fraction viscosity isaround 63 cSt while the aqueous fraction one is about106 cSt these values are considerably higher than those of theTunisian standard fuels (45 cSt) and those of other bio-oilsreported in [27] The water content of the organic fraction isquite high (around 16) and this may be reduced with payingattention to the decantation of the two liquid phases

The FTIR spectrum of bio-oil sample obtained from SSpyrolysis is given in Figure 6(a)The liquid bio-oil seems to bevery complex mixture with a high content of aliphatic groupsindicated by the presence of intense peaks in the absorptionregion between 2800 and 3000 cmminus1 and several peaksbetween 1300 and 1500 cmminus1 imputable to aliphatic CndashHdeformation The aromatic character of the bio-oil sample ismarked by the peak around 1640 cmminus1 corresponding to C=Cin aromatic structures and by many little peaks in the regionbetween 700 and 900 cmminus1

The biochar sample spectrum (Figure 6(b)) shows highcontent of O-containing functions the band centred around3300 cmminus1 due to the presence of OndashH groups and the highintensive band between 1000 and 1100 cmminus1 correspondingto CndashO stretching of carbohydrate and alcohol functionsThe aliphatic groupsrsquo content is indicated mainly by the largebandbetween 1300 and 1500 cmminus1 imputable to aliphaticCndashHdeformation Usually the produced biochar obtained from SSpyrolysis could be used as biofuel (high calorific value) oras chemical adsorbent of pollutants (substitute for activatedcarbon) or as soil fertilizer [35] The potential use of biocharsin these three options depends on their characteristics

343 Gasification Coproducts Characterization Figures 6(c)and 6(d) show the FTIR spectra obtained from condensabletars and solid residue produced from gasification of predriedSS respectively The FTIR condensable tar spectrum showsthe high complexity of these productsThe studied tar sampleis composed of aliphatic compounds and aromatic and O-containing groups with a large variety of organic compoundsThe solid residue spectrum exhibits a slight absorption bandbetween 3200 and 3600 cmminus1 attributable to CndashO stretchingbut a very intensive peak around 1400 cmminus1 corresponding toaliphatic groups We note the presence of many little peaksin the absorption region of 700ndash900 cmminus1 imputable to thearomatic stretching vibrations

BioMed Research International 11

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

0616055050045040035030025020015010005000

minus005minus010minus015minus020

minus0239

C=CndashCHaromCndashO

A

ndashOHndashNH

ndashCH

ndashCH

ndashCH

(cＧminus1)

(a)

minus0123minus005

000005010015020025030035040045050055060065070075080085

0908

C=C CHarom

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

CndashO

A

ndashOHndashNH

ndashCH

(cＧminus1)

(b)

minus00800010203040506070809101112

127

C=C40

0

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHaromCndashO

A

ndashOHndashNH ndashCH

ndashCH

(cＧminus1)

(c)

minus0100001020304050607080910111213

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHarom

ndashOHndashNH

ndashCH

ndashCH

(d)

Figure 6 FTIR spectra of (a) bio-oil sample obtained by SS pyrolysis (b) biochar sample obtained by SS pyrolysis (c) tar sample obtainedby SS gasification and (d) solid residue sample obtained by SS gasification

35 Mathematical Modeling Stoichiometric Model

351 Pyrolysis Balance Equation (8) of pyrolysis is

C120572H120573O120574 + 119909H2Oyields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VO2(8)

120572 120573 and 120574 are determined by the elemental analysis119905 119906 119910 and 119911 are the number of moles of gas species

calculated in Section 353119899C 119899O and 119899H are calculated in Section 351119909 ldquothe number of moles of H2Ordquo is the difference

between the number of moles of oxygen in the products andthat contained in biomass 120574 and it is calculated as follows

119909 = 119910 + 2119911 + 2V + 119899O minus 120574 (in mol) (9)

119899 is the difference between the number of moles of carbonin the initial biomass and that contained in the obtainedproducts and it is calculated as follows

119899 = 120572 minus 119899C minus 119910 minus 119911 minus 119906 (in mol) (10)

119898 is the difference between the number of moles of hydrogenin the reactant and that in the products and is calculated asfollows

119898 = 120573 + 2119909 minus 2119905 minus 4119906 (in mol) (11)

352 Gasification Balance The reaction of gasification isdescribed as follows

C120572H120573O120574 + 119909 (O2 + 367N2)yields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(12)

120572 120573 120574 and 120575 are determined by the elemental analysis

12 BioMed Research International

Table 4 Raw material and syngas stoichiometric model calcula-tions

Element Number of moles

Raw material

Carbon 106Hydrogen 21556Oxygen 1673Nitrogen 322Sulfur 078

Syngas

Mg 41993 g119899N2

000119899O2

000119899CH4

462119899CO 109119899CO2

118119899H2

2286

119905 119906 119910 119911 119901 and 119902 are the number of moles of the gasspecies calculated in Section 353119909 ldquothe number of moles of airrdquo is the difference between

the number of moles of oxygen in the products and thatcontained in the biomass and is calculated as follows

2119909 = 2119902 + 119910 + 2119911 minus 119909 minus 120574 (in mol) (13)

The number of moles 119901 of nitrogen produced is calculated asfollows

119901 = 119909 lowast 376 (in mol) (14)

119899 is the difference between the number of moles of carboncontained in the initial biomass and that contained in theproducts and is calculated as follows

119899 = 120572 minus 119910 minus 119911 minus 119906 (in mol) (15)

119898 is the difference between the number of moles of dihydro-gen in the reactants and that contained in the products and iscalculated as follows

119898 = 120573 minus 2119905 minus 4119906 (in mol) (16)

353 Calculations Table 4 shows the raw material andsyngas stoichiometric model calculations Pyrolysis and gasi-fication balances are respectively illustrated by (17) and (19)

For Pyrolysis

C120572H120573O120574 + 119909H2O 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VHO2(17)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 and 119911 are the number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses data

According to data reported in Table 4 we obtain theglobal SS pyrolysis formula

C106H21556O1673 + 1326H2O 997888rarr

109CO + 118CO2 + 2286H2 + 462CH4

+ C29909H1247 + VHO2

(18)

For Gasification

C120572H120573O120574 + 119909 (O2 + 367N2) 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(19)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 119911 119901 and 119902 are number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses dataAccording to data reported in Table 4 we obtain the

global SS gasification formula

C106H21556O1673 + 127 (O2 + 367N2) 997888rarr

32CO + 68CO2 + 5977H2 + 23CH4

+ C12762H8648 + 467N2 + 047O2

(20)

The obtained pyrolysis and gasification formulas describeaverage degradation of SS compounds under pyrolysis andgasification circumstances The model calculations allow usto study the influence of process parameters and thus topredict the desired products yields

4 Conclusions

In this study pyrolysis and gasification of Tunisian solar driedSS were performed separately using two different laboratory-scale reactors to produce mainly hydrogen-rich syntheticgas Through this work we highlighted the opportunity ofemployment of these two processes in the conversion ofTunisian SS into combustible gases and thus the potential ofsolar dried SS wastes as feedstocks for syngas productionThe released gases from pyrolysis (yield reaching 23wt)and gasification (yield reaching 82wt) present high calorificvalues (around 996MJm3 for pyrolysis and 802MJkg forgasification) due to their high contents of H2 (up to 1085and 732 resp) and CH4 (up to 1762 and 536 resp)The produced syngas should be used either as a fuel or as anintermediate in the production of liquid fuels and chemicalsWe suggest its reuse to supply a part of the energy needed inthe heating part of the reactor in order to enhance the energybalance of the process

Taking into account these experimental and numericalresults it can be concluded that the SS energy recovery viapyrolysis and gasification is a viable method for reducing thevolume of these harmful products with producing valuableproducts and alternative fuels in order to reduce the con-sumption of fossil fuels

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

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Microbiology

BioMed Research International 5

determinate the composition of phytoplankton the ratio ofthe elements does not change The number of carbons 120572 (inthis case 106 according to Redfield formula) is determined inorder to calculate mole number of other elements

Let 1198881 and 1198882 be the following coefficients 1198881 = C12 and1198882 = 1205721198881

The formula of the compound is as follows C120572H120573O120574N120575S120576with

120573 =H lowast 11988821

120574 =O lowast 119888216

120575 =N lowast 119888214

120576 =S lowast 1198882321

(3)

Themass of the compound is1198980 = 12120572+120573+16120574+14120575+321120576(in g)

Let 119898119894 be the initial mass of the compound let 119901119894 be theproportion of the organic element 119894 and let119872119894 be its molarweightThe number of moles of the species 119894 into the biomassis 119899119895 = (119898119894 lowast 119901119895)119872119895 (in mol)

242 Products Yields For determined temperature and heat-ing rate the mass yields are named 119877119887 119877119888 and 119877119892 respec-tively for bio-oil biochar and syngas Let 1198980 be the initialquantity of biomass (in g) 119898119887 119898119888 and 119898119892 are respectivelythe masses of bio-oil biochar and syngas The mass of theproduct p is119898119901 = (119877119901100) lowast 1198980 (in g)

243 SyngasMole Numbers Theproduct gases are CO CO2O2 H2 CH4 C119899H119898 and N2 Let 119891119894 be the fraction of thegas 119894 let119872119894 be its molar mass and let 119898119892 be the mass of theproduct gas The mole number of the gas 119899119894 is calculated bythe following equation 119899119894 = (119898119892 lowast 119891119894)119872119894 (in mol)

For the gasification the masses of produced gases arecalculated as follows119898119892 = 1198980 lowast (1 minus (119890 + 119888)100) (in g) with 119890 being the water

content of the biomass 119888 being the ash content and1198980 beingthe initial mass

244 BiocharMoles Numbers Let119901119895 be the proportion of theorganic element 119895 and let119872119895 be its molar mass The numberofmoles of the species 119895 in the biochar 119899119895 is 119899119895 = (119898119888lowast119901119895)119872119895(in mol)

245 Organic Matter Balance As hypothesized N2 is con-sidered as inert element in pyrolysis and will not be countedin the balance of organic matter

3 Results and Discussion

31 Feed Materials Characteristics

311 Elemental Composition The elemental chemical com-position the physicochemical properties the HHV value

and the Rock-Eval parameters of the predried SS sample areshown in Table 2 The carbon and hydrogen contents arerelatively high (roughly 48wt and 8wt resp) and compa-rable to those of other SS used in pyrolysis and advanced by[16 18 30] and to some lignocellulosicmaterials [9] (Table 2)The nitrogen and sulphur contents are respectively about171 wt and 096wt these contents are lower than thoseobtained for other SS samples (from 4 to 8 for nitrogenand from 06 to 76 wt for sulphur Table 2) The highnitrogen content observed in studied SS is attributed to theprotein fraction contained in microorganisms used for waterpurification through biological degradation [31] The oxygencontent is around 10 and it is significantly lower than thoseof lignocellulosic residues and SS samples (approximatelybetween 188 and 537 Table 2)

These differences in elemental composition between SSsamples cited in previous studies and those of this work couldbe explained by the difference in the origin and the treatmentsin wastewater plant [31]

Proximate analysis (Table 2) showed that SS moisturecontent is about 949 and this low humidity was reachedusing a solar drying technologyThe purpose of the SS dryingwas to achieve water content less than 10 since most ofthe previous studies on SS pyrolysis and gasification wereapplied for raw materials with humidity between 5 and 35[1 16 18 22] in order to reduce the occurrence of steamreforming reactions at high temperatures and to increase theproduction of hydrogen-rich gasThe amounts of ash andVMin SS are quite high (around 3080 and 5881 resp) andthey are in the same range of SS used in previous pyrolysisstudies and reported by other researchers [1 18 22 31]

The Rock-Eval hydrogen index (HI) is around 476mgof hydrocarbons by g of Total Organic Carbon (mg HCgTOC) indicating a high potential of hydrogen productionfor the predried SS In fact measured usually for evaluatingthe source rock maturity in petroleum prospection the HIparameter indicates the richness of studied SS in hydrogenwhich can be converted into gaseous hydrogenated compo-nents via pyrolysis For the studied samples the HI valueis very high confirming them to be appropriate substratesfor the production of hydrogen-rich synthesis gas suchas H2 CH4 and C119899H119898 SS calorific value is quite high(around 25MJkg) compared to those of other SS used forpyrolysis experiments (around 17MJkg [18] and between 9and 12MJkg [1 16])

312 FTIR Functional Groups Composition Figure 2(a)shows the IR spectrum obtained from predried SS The SSFTIR spectrum contains a large band between 3200 and3600 cmminus1 attributed to OndashH stretching vibration of car-boxylic and alcoholic groups The presence of the absorptionpeaks between 2800 and 3000 cmminus1 and around 1400 cmminus1indicates the high content of aliphatic functions originatedmainly from lipid fraction contained in SS The richnessof aromatic groups is revealed by the large band at around1640 cmminus1 related to C=C and other little peaks around700ndash900 cmminus1 attributed to CndashH in aromatic structures Theabundance of O-containing groups is observed essentially by

6 BioMed Research International

Table 2 Characteristics of studied solar dried SS and others used in thermochemical conversion studies according to literature

Ultimate analysis ()Studied solar dried SS Thipkhunthod et al 2007 Tsai et al 2009 Fonts et al 2012 Chen et al 2015

Sewage sludge Lignocellulosic biomassC 4821 plusmn 1 276ndash484 316ndash423 231ndash399 421ndash493H 817 plusmn 03 65ndash74 49ndash63 38ndash59 55ndash61O 1015 353ndash537 318ndash356 188ndash235 442ndash509N 171 plusmn 01 39ndash74 55ndash77 25ndash79 00ndash09S 096 plusmn 01 12ndash76 06ndash14 08ndash10 01ndash08

Proximate analysis ()Moisture content 949 plusmn 03 32ndash76 160ndash180 15ndash71 36ndash103Ash content 3080 plusmn 2 434ndash714 242ndash449 226ndash520 05ndash79Volatile matter 5881 plusmn 3 259ndash524 390ndash548 383ndash668 718ndash832Fixed carbon 090 27ndash64 mdash 08ndash197 57ndash174Hydrogen indexlowast 476 mdash mdash mdash mdashHHV (MJkg) 2482 mdash mdash mdash mdashlowast in mg hydrocarbong organic carbon

4000

3600

3200

2800

2400

2000

1800

1600

1400

1200

1000 80

0

600

400

minus0059minus004minus002minus000

002004006A008010012014016

0183ndashOHndashNH

C=C

ndashCH

ndashCH

CndashH

(cＧminus1)

(a)

50 100

150

200

250

300

350

400

450

500

550

600

650

700

TG (m

g)

minus10

minus8

minus6

minus4

minus2

0

Hea

t flow

(V

)

minus4minus3minus2minus1012345

dTG

(mg

min

)minus040minus035minus030minus025minus020minus015minus010minus005

000

Exo

Sample temperature (∘C)

(b)

Figure 2 FTIR spectrum (a) and TGADTA diagrams (b) for solar dried SS sample

the presence of the large absorption band around 1037 cmminus1assigned to CndashO stretching of carbohydrates and alcoholfunctions and reflecting the concurrence of exopolysaccha-rides released by microorganisms of predried SS andorfrom wastewater itself The FTIR spectroscopy structuralcharacterization of the predried SS reveals the high organiccharacter of theses wastes and mainly the oxygenated andaromatic functional groupsrsquo richness It may be concludedthat these wastes are suitable feedstock for biofuels produc-tion through pyrolysis and gasification processes

313 Thermogravimetric Behaviour The results of the ther-mogravimetric (TG) and differential thermal (DT) analysesof predried SS are given in Figure 2(b) The TG curve ispresented in green color indicating the variation of the massloss (expressed in mg) of studied SS under heating whereasthe curve in red color (dTG) shows the evolution of the mass

loss rate (expressed in mgmin) The blue curve indicatesthe heat flow (expressed in 120583V) used during experimentsThe thermogravimetric analysis was applied in this studyto have prior knowledge of initial and final temperaturesfor thermal degradation of SS As can be observed fromFigure 2(b) the predried SS thermal decomposition and thusthe loss of mass took place in two big steps the initial weightloss occurring between 50∘C and 100∘C and related to adrying phase (loss of physically absorbed water molecules) Itcorresponds to amass loss around 464 of the originalmassA second strong weight loss (around 4643 of its originalmass) occurs between 200∘C and 600∘C with a large peakcentred at 337∘C and a shoulder between 220 and 320∘CThisstep corresponds mainly to the volatilization of volatiles inSS and thus to the degradation of main organic componentscontained in SS In reality various organic compoundsdecompose between 200 and 400∘C hemicelluloses cellulose

BioMed Research International 7

536

1311

8153

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Prod

ucts

yiel

ds (w

t)

TarsSolid residueSyngas

(a)

4030 39583095

3958

46934967

20121350

1938

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

10 15 20

Prod

ucts

yiel

ds (w

t)

Bio-oilBiocharSyngas

Heating rate (∘Cmin)

(b)

2739

4030

48465009 4809

2977

2247

1161

2177

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

500 550 600

Prod

ucts

yiel

ds (w

t)

Pyrolysis temperature (∘C)

Bio-oilBiocharSyngas

(c)

Figure 3 SS pyrolysis products distribution (a) variable pyrolysis temperature and invariable heating rate 15∘Cmin (b) variable heatingrate and invariable temperature 550∘C (c) SS gasification products distribution

and lignins leather some N-containing compounds such asaliphatic amino acids and aromatic compounds contained inplastic materials But due to the great heterogeneity of thestudied SS chemical composition it is difficult to attributethis decomposition to specific organic compounds After600∘C SS sample showed a weight loss of 316 of its originalmass attributed mainly to the decomposition of inorganicmaterials

32 Pyrolysis and Gasification Products Distribution Pyrol-ysis experimental conditions influence the products distri-bution and properties Among these parameters pyrolysisfinal temperature has the largest effect on the products yieldsThe pyrolysis temperature has been evaluated based on thethermogravimetric results and the previous studies of SSpyrolysis found in the literature Figure 3(a) exhibits theproducts (bio-oil biochar and syngas) distribution of SS

8 BioMed Research International

pyrolysis at different final temperatures (500 550 and 600∘C)and at an invariable heating rate (15∘Cmin) and a constantcooling temperature (minus5∘C) As it can be seen an increasein pyrolysis temperature (from 500 to 600∘C) results in adecrease in biochar yield (from 50 to 30) and an increasein liquid fraction yield (from 27 to 48) due probably to thepromotion of devolatilization reactions At higher tempera-tures secondary reactions involving volatiles such as thermalcracking are improved leading to a reduction in the liquidyield and an increase in the gas yieldThe decrease in biocharyield is possibly related also to further pyrolysis conversionand thus to a greater primary decomposition of the initialfeedstock or to secondary reactions of the solid residue [13]The syngas yield is variable in all conditions the pyrolysisgas amount is not very high (does not exceed 23) andthe optimum pyrolysis temperature obtained for maximumsyngas production is around 500∘CBy investigating the effectof reaction temperature (in the range of 450ndash600∘C) on theyields of SS pyrolysis products [1] obtained a maximum gasyield of 20 in dry and ash-free basis at 600∘C whereas [32]reported a maximum yield of gaseous products in the rangeof 15ndash25 at high temperature (700∘C) Reference [17] bystudying the influence of pyrolysis temperature on productsdistribution reported that gas yield remains almost constant(around 20ndash22) as the pyrolysis temperature increased from350 to 550∘C but above 550∘C a significant increase in gasproduction is observed (reaching a gas yield around 32)

Apart from temperature heating rate also plays a signif-icant role in products yields variation during SS pyrolysisFigure 3(b) shows the influence of heating rate variation onproducts yields distribution at an invariable final temperature(550∘C) and a constant cooling temperature (minus5∘C) It can beseen that an increase in the heating rate leads to a decreasein the liquid fraction and to an increase in the solid fractionwhile the gas fraction yield remains variableThese results arein agreement with the literature Reference [33] using twoheating rates (5∘Cmin and 60∘Cmin) demonstrated that theincrease in heating rate gives an increase in liquid productsyield and a decrease in biochar yield

Regarding the gasification process some operationalproblems were encountered in the measurement of productsyields such as (i) tars condensation and deposits duringcooling of the gasifier and at the outlet of the reactor and(ii) presence of tars in the produced syngas Roughly theobtained yields given in Figure 3(c) are as follows 82 ofsyngas 13 of solid residue and 5 of tars

33 Gasification Reactor Temperature Distribution In orderto distinguish the different zones within the gasificationreactor the temperature data recorded inside the gasifierwereexploited Figure 4 shows the inside reactor axial temperatureevolution obtained during the predried SS gasification expe-riences using five active thermocouples (from T1 to T5) Thetemperature curves recorded by thermocouples T1 (orangecolor) and T2 (green color) show a regular temperaturevariation around 50∘C until 100min from the beginningof the gasification experiment After that the temperatureincreased slowly for T1 and suddenly for T2 to reach 240∘Cand 290∘C respectively which were maintained until the

0

100

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000Time (sec)

T1 (∘C)

T2 (∘C)

T3 (∘C)

T4 (∘C)

T5 (∘C)

Tem

pera

ture

(∘C)

Figure 4 Reactor axial temperature evolution during solar dried SSgasification process

end of the experiment This corresponds to the drying zonein the reactor In this drying zone moisture content of thebiomass is reduced considerably The temperature variationsrecorded by thermocouples T3 (pink color) and T4 (bluecolor) show a regular evolution from room temperature toa maximum of 520∘C and by the end of the experimentto 750∘C as maximum temperature indicating the pyrolysisphase In this pyrolysis stage the thermal cracking of biomassoccurs in the absence of oxygen and solid residue (charcoal)and volatile vapors (containing carbon monoxide hydrogencarbon dioxide and hydrocarbon gases) are released [22]Thermocouple T5 (black color) recorded temperatures inthe gasification zone as it reaches rapidly high temperatureabove 900∘CThe gasification process of predried SS samplesstarted at moderate temperatures (between 600 and 700∘C)and achieves high temperatures (above 900∘C) at the end ofthe gasification experiment In this reduction area severalreactions occur and the temperature ranges between 800 and1000∘C These reactions are mostly endothermic in natureThe distribution of the gasifier axial temperature enables usto follow different mechanisms occurring throughout thegasification process and thus to delineate the different zoneswithin the reactor such us drying pyrolysis combustion andgasification Furthermore the temperature evolution showsthat the predried SS gasification reactions take place at hightemperature (above 900∘C) In this gasification area severalreduction reactions occur The main reactions in this zone asdescribed by [22] are as follows

Water-Gas Reaction

C +H2O 997888rarr CO +H2 Δ119867 = 1314 kJmol (4)

BioMed Research International 9

0

2

4

6

8

10

12

0102030405060708090

100

300 350 400 450 500 550 600 550 500 450 400 350 300

Calc

ulat

ed L

HV

(MJk

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2

（4

n（m

（2

2

(a)

0123456789

0102030405060708090

100

300 400 500 600 700 800 900 800 700 600 500

Calc

ulat

ed L

HV

(MJK

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2 2

（4

n（m

（2

2

(b)

Figure 5 Syngas chemical composition and LHV evolution during (a) SS pyrolysis process (600∘C and 20∘Cminminus1) and (b) SS gasificationprocess

Boudouard Reaction

C + CO2 997888rarr 2CO Δ119867 = 1726 kJmol (5)

Shift Reaction

CO2 +H2 997888rarr CO +H2O Δ119867 = 42 kJmol (6)

Methane Reaction

C + 2H2 997888rarr CH4 Δ119867 = 75 kJmol (7)

In total the fixed-bed downdraft gasifier is recommendedequipment to study the gasification reactions and mecha-nisms at laboratory scale and to produce clean gas but themain disadvantages of this type of gasifier are its low ther-mal efficiency and the great difficulties related to handlingbiomass with high moisture and ash contents [22]

34 Pyrolysis and Gasification Products Characterization

341 Syngas Composition

(1) Pyrolysis Syngas Composition The syngas chemical com-position obtained throughout SS pyrolysis is shown in Fig-ure 5(a) The major gaseous products obtained from SSpyrolysis are CH4 (up to 1762) CO2 (up to 1203)H2 (up to 1085) CO (up to 726) and C119899H119898 (up to430) From Figure 5(a) it could be roughly seen that thevariation of several produced gases is almost constant witha high release at the beginning of the experiment (from300∘C) to achieve maximum of combustible gas productionat 600∘C and finally a gradual decrease marking the end ofthe pyrolysis reactions Among combustible gases CH4 andH2 are found to be the most abundant compounds of the

produced gases from SS pyrolysis The H2 high content inthe syngas mixture produced by pyrolysis could be explainedby the catalytic effect of the minerals contained in studiedSS (ash content around 3080) This catalytic effect in SSpyrolysis was highlighted by many authors [12 16] whostudied the correlation between the H2 percentage producedby pyrolysis of SS and the SS ash content and demonstratedthat the catalytic effect of the ash in the dehydrogenationreactions enhances the H2 production whereas the highH2 production is often correlated directly to the high ashcontent of SS which have a catalytic effect during thermalcracking and mainly in the dehydrogenation reactions [1216] Moreover the formation of CO and CO2 could beattributed to the decomposition of oxygenated groups suchas decarboxylation and decarbonylation [32] Other worksthat were conducted on SS pyrolysis have reported similar gascompositions Reference [12] presented a syngas compositionproduced from SS pyrolysis with a high yield (between 45and 66) of CO and H2 and reported that the gas fromthe conventional oven is much richer in hydrocarbons (25)than that from themicrowave ovens (6ndash11) According to [1]that studied SS flash pyrolysis in a conical spouted bed reactorat 600∘C the gas mixture composition is as follows 35 ofCO2 23 of CO 23 of H2 and 24 of C1ndashC4 Reference[16] obtained with the pyrolysis of three SS samples a gasmixture containing up to 60 of CO2 34 of CO 28 ofH2 11 of CH4 and 2-3 of C119899H119898

The calorific value (LHV) of the produced gas mixtureobtained under the pyrolysis conditions used in the presentstudy reaches a maximum of 996MJkg indicating a highcontent of combustible gases in this gaseous mixture Thisrelatively elevated heating value of the gas mixture can bevalorized as an alternative source of heating for the pyrolysisreactor The obtained heating values of gases are in the samerange as those reported by previous studies In fact the

10 BioMed Research International

heating values of gases from conventional pyrolysis were130ndash140MJm3 whereas with the microwave method theheating values ranged from 66 to 86MJm3 [11] Reference[33] that studied the pyrolysis of SS reported that the releasedgases have a maximum heating value around 25MJm3

(2) Gasification Syngas Composition The syngas chemicalcomposition analysis throughout the gasification experiment(Figure 5(b)) reveals that the obtained syngas is a mixtureof the following main components CO2 (up to 1843) CO(up to 76) H2 (up to 732) CH4 (up to 536) andC119899H119898 (up to 236) As can be observed in Figure 5(b)when the reactor temperature increased the CO and CO2concentrations increased due to decarbonylation and decar-boxylation reactions at high temperatures H2 concentrationincreased also with the temperature increase with a max-imum around 732wt at nearly 900∘C and this is due tonot only the cracking reactions but also dehydrogenationreactions promoted by the catalytic effect of the inorganicfraction [1 16] CH4 and C119899H119898 showed the same trendwith a slight variation from the beginning These drawndata are in agreement with those described by [2] where atypical gasification gaseousmixture is characterized by a highhydrogen content (H2 889ndash1117 vol) It contains also othercombustible compounds including CO (628ndash1077 vol)CH4 (126ndash209 vol) carbon dioxide and some light hydro-carbons Similar observations have been advanced by [17] thatstudied SS gasification using downdraft reactor and indicatedthat produced syngas is composed mainly of combustiblegases such as H2 (880ndash1115 vol) CO (631ndash1063 vol)CH4 (125ndash207 vol) and C119899H119898 (076ndash110 vol) and non-combustible gases such as N2 and CO2

The heating value of the syngas obtained under thegasification conditions used in the present study reachesa maximum of 802MJkg This calorific value is higherthan those reported for SS pyrolysis Reference [18] reportedgross heating values ranging from 487 to 555MJkg forsyngas produced from SS gasification in a downdraft gasifierwhereas [34] advanced LHV values ranging between 415 and709MJkg for syngas produced from two types of SS

342 Bio-Oil and Biochar Properties The bio-oil elementalcomposition is as follows C 5659wt H 824wt N396wt S 032 wt and O 3089wt The obtained car-bon hydrogen and sulphur contents are lower than thosefound by other authors from pyrolysis of SS Thus [34]obtained for bio-oils produced from conventional pyrolysisof SS carbon content between 709 and 845 wt hydrogencontent between 103 and 124 wt and sulphur contentbetween 02 and 06 wt Reference [33] reported for organicfraction of SS pyrolysis liquids between 494 and 626wtfor carbon and between 98 wt and 115 wt for hydrogennitrogen and sulphur contents are almost invariable [33 35]The knowledge of elemental composition (mainly carbonhydrogen and sulphur contents) is necessary for potentialutilization of these bio-oils as biofuels or for further process-ing to petrochemicals or biodiesel

The bio-oil density at 15∘C kinematic viscosity and watercontents of both organic and aqueous fractions from SS

Table 3 Fuel properties of liquid fractions obtained from SSpyrolysis (at 550∘C and 15∘Cmin)

Density (15∘C)(KgL)

Viscosity(40∘C)(mm2s)

Water content()

Organic fraction 09743 63 16Aqueousfraction 1 106 25

pyrolysis are reported in Table 3The organic fraction densityaround 09743Kgm3 is quite higher than those required bythe Tunisian standard fuels (between 820 and 860 kgm3)and also higher than those of similar bio-oils obtained fromdifferent feedstocks [27] The organic fraction viscosity isaround 63 cSt while the aqueous fraction one is about106 cSt these values are considerably higher than those of theTunisian standard fuels (45 cSt) and those of other bio-oilsreported in [27] The water content of the organic fraction isquite high (around 16) and this may be reduced with payingattention to the decantation of the two liquid phases

The FTIR spectrum of bio-oil sample obtained from SSpyrolysis is given in Figure 6(a)The liquid bio-oil seems to bevery complex mixture with a high content of aliphatic groupsindicated by the presence of intense peaks in the absorptionregion between 2800 and 3000 cmminus1 and several peaksbetween 1300 and 1500 cmminus1 imputable to aliphatic CndashHdeformation The aromatic character of the bio-oil sample ismarked by the peak around 1640 cmminus1 corresponding to C=Cin aromatic structures and by many little peaks in the regionbetween 700 and 900 cmminus1

The biochar sample spectrum (Figure 6(b)) shows highcontent of O-containing functions the band centred around3300 cmminus1 due to the presence of OndashH groups and the highintensive band between 1000 and 1100 cmminus1 correspondingto CndashO stretching of carbohydrate and alcohol functionsThe aliphatic groupsrsquo content is indicated mainly by the largebandbetween 1300 and 1500 cmminus1 imputable to aliphaticCndashHdeformation Usually the produced biochar obtained from SSpyrolysis could be used as biofuel (high calorific value) oras chemical adsorbent of pollutants (substitute for activatedcarbon) or as soil fertilizer [35] The potential use of biocharsin these three options depends on their characteristics

343 Gasification Coproducts Characterization Figures 6(c)and 6(d) show the FTIR spectra obtained from condensabletars and solid residue produced from gasification of predriedSS respectively The FTIR condensable tar spectrum showsthe high complexity of these productsThe studied tar sampleis composed of aliphatic compounds and aromatic and O-containing groups with a large variety of organic compoundsThe solid residue spectrum exhibits a slight absorption bandbetween 3200 and 3600 cmminus1 attributable to CndashO stretchingbut a very intensive peak around 1400 cmminus1 corresponding toaliphatic groups We note the presence of many little peaksin the absorption region of 700ndash900 cmminus1 imputable to thearomatic stretching vibrations

BioMed Research International 11

400

600

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1400

1600

1800

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2400

2800

3200

3600

4000

0616055050045040035030025020015010005000

minus005minus010minus015minus020

minus0239

C=CndashCHaromCndashO

A

ndashOHndashNH

ndashCH

ndashCH

ndashCH

(cＧminus1)

(a)

minus0123minus005

000005010015020025030035040045050055060065070075080085

0908

C=C CHarom

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

CndashO

A

ndashOHndashNH

ndashCH

(cＧminus1)

(b)

minus00800010203040506070809101112

127

C=C40

0

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHaromCndashO

A

ndashOHndashNH ndashCH

ndashCH

(cＧminus1)

(c)

minus0100001020304050607080910111213

400

600

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1000

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1400

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1800

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2400

2800

3200

3600

4000

ndashCHarom

ndashOHndashNH

ndashCH

ndashCH

(d)

Figure 6 FTIR spectra of (a) bio-oil sample obtained by SS pyrolysis (b) biochar sample obtained by SS pyrolysis (c) tar sample obtainedby SS gasification and (d) solid residue sample obtained by SS gasification

35 Mathematical Modeling Stoichiometric Model

351 Pyrolysis Balance Equation (8) of pyrolysis is

C120572H120573O120574 + 119909H2Oyields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VO2(8)

120572 120573 and 120574 are determined by the elemental analysis119905 119906 119910 and 119911 are the number of moles of gas species

calculated in Section 353119899C 119899O and 119899H are calculated in Section 351119909 ldquothe number of moles of H2Ordquo is the difference

between the number of moles of oxygen in the products andthat contained in biomass 120574 and it is calculated as follows

119909 = 119910 + 2119911 + 2V + 119899O minus 120574 (in mol) (9)

119899 is the difference between the number of moles of carbonin the initial biomass and that contained in the obtainedproducts and it is calculated as follows

119899 = 120572 minus 119899C minus 119910 minus 119911 minus 119906 (in mol) (10)

119898 is the difference between the number of moles of hydrogenin the reactant and that in the products and is calculated asfollows

119898 = 120573 + 2119909 minus 2119905 minus 4119906 (in mol) (11)

352 Gasification Balance The reaction of gasification isdescribed as follows

C120572H120573O120574 + 119909 (O2 + 367N2)yields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(12)

120572 120573 120574 and 120575 are determined by the elemental analysis

12 BioMed Research International

Table 4 Raw material and syngas stoichiometric model calcula-tions

Element Number of moles

Raw material

Carbon 106Hydrogen 21556Oxygen 1673Nitrogen 322Sulfur 078

Syngas

Mg 41993 g119899N2

000119899O2

000119899CH4

462119899CO 109119899CO2

118119899H2

2286

119905 119906 119910 119911 119901 and 119902 are the number of moles of the gasspecies calculated in Section 353119909 ldquothe number of moles of airrdquo is the difference between

the number of moles of oxygen in the products and thatcontained in the biomass and is calculated as follows

2119909 = 2119902 + 119910 + 2119911 minus 119909 minus 120574 (in mol) (13)

The number of moles 119901 of nitrogen produced is calculated asfollows

119901 = 119909 lowast 376 (in mol) (14)

119899 is the difference between the number of moles of carboncontained in the initial biomass and that contained in theproducts and is calculated as follows

119899 = 120572 minus 119910 minus 119911 minus 119906 (in mol) (15)

119898 is the difference between the number of moles of dihydro-gen in the reactants and that contained in the products and iscalculated as follows

119898 = 120573 minus 2119905 minus 4119906 (in mol) (16)

353 Calculations Table 4 shows the raw material andsyngas stoichiometric model calculations Pyrolysis and gasi-fication balances are respectively illustrated by (17) and (19)

For Pyrolysis

C120572H120573O120574 + 119909H2O 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VHO2(17)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 and 119911 are the number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses data

According to data reported in Table 4 we obtain theglobal SS pyrolysis formula

C106H21556O1673 + 1326H2O 997888rarr

109CO + 118CO2 + 2286H2 + 462CH4

+ C29909H1247 + VHO2

(18)

For Gasification

C120572H120573O120574 + 119909 (O2 + 367N2) 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(19)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 119911 119901 and 119902 are number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses dataAccording to data reported in Table 4 we obtain the

global SS gasification formula

C106H21556O1673 + 127 (O2 + 367N2) 997888rarr

32CO + 68CO2 + 5977H2 + 23CH4

+ C12762H8648 + 467N2 + 047O2

(20)

The obtained pyrolysis and gasification formulas describeaverage degradation of SS compounds under pyrolysis andgasification circumstances The model calculations allow usto study the influence of process parameters and thus topredict the desired products yields

4 Conclusions

In this study pyrolysis and gasification of Tunisian solar driedSS were performed separately using two different laboratory-scale reactors to produce mainly hydrogen-rich syntheticgas Through this work we highlighted the opportunity ofemployment of these two processes in the conversion ofTunisian SS into combustible gases and thus the potential ofsolar dried SS wastes as feedstocks for syngas productionThe released gases from pyrolysis (yield reaching 23wt)and gasification (yield reaching 82wt) present high calorificvalues (around 996MJm3 for pyrolysis and 802MJkg forgasification) due to their high contents of H2 (up to 1085and 732 resp) and CH4 (up to 1762 and 536 resp)The produced syngas should be used either as a fuel or as anintermediate in the production of liquid fuels and chemicalsWe suggest its reuse to supply a part of the energy needed inthe heating part of the reactor in order to enhance the energybalance of the process

Taking into account these experimental and numericalresults it can be concluded that the SS energy recovery viapyrolysis and gasification is a viable method for reducing thevolume of these harmful products with producing valuableproducts and alternative fuels in order to reduce the con-sumption of fossil fuels

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

6 BioMed Research International

Table 2 Characteristics of studied solar dried SS and others used in thermochemical conversion studies according to literature

Ultimate analysis ()Studied solar dried SS Thipkhunthod et al 2007 Tsai et al 2009 Fonts et al 2012 Chen et al 2015

Sewage sludge Lignocellulosic biomassC 4821 plusmn 1 276ndash484 316ndash423 231ndash399 421ndash493H 817 plusmn 03 65ndash74 49ndash63 38ndash59 55ndash61O 1015 353ndash537 318ndash356 188ndash235 442ndash509N 171 plusmn 01 39ndash74 55ndash77 25ndash79 00ndash09S 096 plusmn 01 12ndash76 06ndash14 08ndash10 01ndash08

Proximate analysis ()Moisture content 949 plusmn 03 32ndash76 160ndash180 15ndash71 36ndash103Ash content 3080 plusmn 2 434ndash714 242ndash449 226ndash520 05ndash79Volatile matter 5881 plusmn 3 259ndash524 390ndash548 383ndash668 718ndash832Fixed carbon 090 27ndash64 mdash 08ndash197 57ndash174Hydrogen indexlowast 476 mdash mdash mdash mdashHHV (MJkg) 2482 mdash mdash mdash mdashlowast in mg hydrocarbong organic carbon

4000

3600

3200

2800

2400

2000

1800

1600

1400

1200

1000 80

0

600

400

minus0059minus004minus002minus000

002004006A008010012014016

0183ndashOHndashNH

C=C

ndashCH

ndashCH

CndashH

(cＧminus1)

(a)

50 100

150

200

250

300

350

400

450

500

550

600

650

700

TG (m

g)

minus10

minus8

minus6

minus4

minus2

0

Hea

t flow

(V

)

minus4minus3minus2minus1012345

dTG

(mg

min

)minus040minus035minus030minus025minus020minus015minus010minus005

000

Exo

Sample temperature (∘C)

(b)

Figure 2 FTIR spectrum (a) and TGADTA diagrams (b) for solar dried SS sample

the presence of the large absorption band around 1037 cmminus1assigned to CndashO stretching of carbohydrates and alcoholfunctions and reflecting the concurrence of exopolysaccha-rides released by microorganisms of predried SS andorfrom wastewater itself The FTIR spectroscopy structuralcharacterization of the predried SS reveals the high organiccharacter of theses wastes and mainly the oxygenated andaromatic functional groupsrsquo richness It may be concludedthat these wastes are suitable feedstock for biofuels produc-tion through pyrolysis and gasification processes

313 Thermogravimetric Behaviour The results of the ther-mogravimetric (TG) and differential thermal (DT) analysesof predried SS are given in Figure 2(b) The TG curve ispresented in green color indicating the variation of the massloss (expressed in mg) of studied SS under heating whereasthe curve in red color (dTG) shows the evolution of the mass

loss rate (expressed in mgmin) The blue curve indicatesthe heat flow (expressed in 120583V) used during experimentsThe thermogravimetric analysis was applied in this studyto have prior knowledge of initial and final temperaturesfor thermal degradation of SS As can be observed fromFigure 2(b) the predried SS thermal decomposition and thusthe loss of mass took place in two big steps the initial weightloss occurring between 50∘C and 100∘C and related to adrying phase (loss of physically absorbed water molecules) Itcorresponds to amass loss around 464 of the originalmassA second strong weight loss (around 4643 of its originalmass) occurs between 200∘C and 600∘C with a large peakcentred at 337∘C and a shoulder between 220 and 320∘CThisstep corresponds mainly to the volatilization of volatiles inSS and thus to the degradation of main organic componentscontained in SS In reality various organic compoundsdecompose between 200 and 400∘C hemicelluloses cellulose

BioMed Research International 7

536

1311

8153

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Prod

ucts

yiel

ds (w

t)

TarsSolid residueSyngas

(a)

4030 39583095

3958

46934967

20121350

1938

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

10 15 20

Prod

ucts

yiel

ds (w

t)

Bio-oilBiocharSyngas

Heating rate (∘Cmin)

(b)

2739

4030

48465009 4809

2977

2247

1161

2177

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

500 550 600

Prod

ucts

yiel

ds (w

t)

Pyrolysis temperature (∘C)

Bio-oilBiocharSyngas

(c)

Figure 3 SS pyrolysis products distribution (a) variable pyrolysis temperature and invariable heating rate 15∘Cmin (b) variable heatingrate and invariable temperature 550∘C (c) SS gasification products distribution

and lignins leather some N-containing compounds such asaliphatic amino acids and aromatic compounds contained inplastic materials But due to the great heterogeneity of thestudied SS chemical composition it is difficult to attributethis decomposition to specific organic compounds After600∘C SS sample showed a weight loss of 316 of its originalmass attributed mainly to the decomposition of inorganicmaterials

32 Pyrolysis and Gasification Products Distribution Pyrol-ysis experimental conditions influence the products distri-bution and properties Among these parameters pyrolysisfinal temperature has the largest effect on the products yieldsThe pyrolysis temperature has been evaluated based on thethermogravimetric results and the previous studies of SSpyrolysis found in the literature Figure 3(a) exhibits theproducts (bio-oil biochar and syngas) distribution of SS

8 BioMed Research International

pyrolysis at different final temperatures (500 550 and 600∘C)and at an invariable heating rate (15∘Cmin) and a constantcooling temperature (minus5∘C) As it can be seen an increasein pyrolysis temperature (from 500 to 600∘C) results in adecrease in biochar yield (from 50 to 30) and an increasein liquid fraction yield (from 27 to 48) due probably to thepromotion of devolatilization reactions At higher tempera-tures secondary reactions involving volatiles such as thermalcracking are improved leading to a reduction in the liquidyield and an increase in the gas yieldThe decrease in biocharyield is possibly related also to further pyrolysis conversionand thus to a greater primary decomposition of the initialfeedstock or to secondary reactions of the solid residue [13]The syngas yield is variable in all conditions the pyrolysisgas amount is not very high (does not exceed 23) andthe optimum pyrolysis temperature obtained for maximumsyngas production is around 500∘CBy investigating the effectof reaction temperature (in the range of 450ndash600∘C) on theyields of SS pyrolysis products [1] obtained a maximum gasyield of 20 in dry and ash-free basis at 600∘C whereas [32]reported a maximum yield of gaseous products in the rangeof 15ndash25 at high temperature (700∘C) Reference [17] bystudying the influence of pyrolysis temperature on productsdistribution reported that gas yield remains almost constant(around 20ndash22) as the pyrolysis temperature increased from350 to 550∘C but above 550∘C a significant increase in gasproduction is observed (reaching a gas yield around 32)

Apart from temperature heating rate also plays a signif-icant role in products yields variation during SS pyrolysisFigure 3(b) shows the influence of heating rate variation onproducts yields distribution at an invariable final temperature(550∘C) and a constant cooling temperature (minus5∘C) It can beseen that an increase in the heating rate leads to a decreasein the liquid fraction and to an increase in the solid fractionwhile the gas fraction yield remains variableThese results arein agreement with the literature Reference [33] using twoheating rates (5∘Cmin and 60∘Cmin) demonstrated that theincrease in heating rate gives an increase in liquid productsyield and a decrease in biochar yield

Regarding the gasification process some operationalproblems were encountered in the measurement of productsyields such as (i) tars condensation and deposits duringcooling of the gasifier and at the outlet of the reactor and(ii) presence of tars in the produced syngas Roughly theobtained yields given in Figure 3(c) are as follows 82 ofsyngas 13 of solid residue and 5 of tars

33 Gasification Reactor Temperature Distribution In orderto distinguish the different zones within the gasificationreactor the temperature data recorded inside the gasifierwereexploited Figure 4 shows the inside reactor axial temperatureevolution obtained during the predried SS gasification expe-riences using five active thermocouples (from T1 to T5) Thetemperature curves recorded by thermocouples T1 (orangecolor) and T2 (green color) show a regular temperaturevariation around 50∘C until 100min from the beginningof the gasification experiment After that the temperatureincreased slowly for T1 and suddenly for T2 to reach 240∘Cand 290∘C respectively which were maintained until the

0

100

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000Time (sec)

T1 (∘C)

T2 (∘C)

T3 (∘C)

T4 (∘C)

T5 (∘C)

Tem

pera

ture

(∘C)

Figure 4 Reactor axial temperature evolution during solar dried SSgasification process

end of the experiment This corresponds to the drying zonein the reactor In this drying zone moisture content of thebiomass is reduced considerably The temperature variationsrecorded by thermocouples T3 (pink color) and T4 (bluecolor) show a regular evolution from room temperature toa maximum of 520∘C and by the end of the experimentto 750∘C as maximum temperature indicating the pyrolysisphase In this pyrolysis stage the thermal cracking of biomassoccurs in the absence of oxygen and solid residue (charcoal)and volatile vapors (containing carbon monoxide hydrogencarbon dioxide and hydrocarbon gases) are released [22]Thermocouple T5 (black color) recorded temperatures inthe gasification zone as it reaches rapidly high temperatureabove 900∘CThe gasification process of predried SS samplesstarted at moderate temperatures (between 600 and 700∘C)and achieves high temperatures (above 900∘C) at the end ofthe gasification experiment In this reduction area severalreactions occur and the temperature ranges between 800 and1000∘C These reactions are mostly endothermic in natureThe distribution of the gasifier axial temperature enables usto follow different mechanisms occurring throughout thegasification process and thus to delineate the different zoneswithin the reactor such us drying pyrolysis combustion andgasification Furthermore the temperature evolution showsthat the predried SS gasification reactions take place at hightemperature (above 900∘C) In this gasification area severalreduction reactions occur The main reactions in this zone asdescribed by [22] are as follows

Water-Gas Reaction

C +H2O 997888rarr CO +H2 Δ119867 = 1314 kJmol (4)

BioMed Research International 9

0

2

4

6

8

10

12

0102030405060708090

100

300 350 400 450 500 550 600 550 500 450 400 350 300

Calc

ulat

ed L

HV

(MJk

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2

（4

n（m

（2

2

(a)

0123456789

0102030405060708090

100

300 400 500 600 700 800 900 800 700 600 500

Calc

ulat

ed L

HV

(MJK

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2 2

（4

n（m

（2

2

(b)

Figure 5 Syngas chemical composition and LHV evolution during (a) SS pyrolysis process (600∘C and 20∘Cminminus1) and (b) SS gasificationprocess

Boudouard Reaction

C + CO2 997888rarr 2CO Δ119867 = 1726 kJmol (5)

Shift Reaction

CO2 +H2 997888rarr CO +H2O Δ119867 = 42 kJmol (6)

Methane Reaction

C + 2H2 997888rarr CH4 Δ119867 = 75 kJmol (7)

In total the fixed-bed downdraft gasifier is recommendedequipment to study the gasification reactions and mecha-nisms at laboratory scale and to produce clean gas but themain disadvantages of this type of gasifier are its low ther-mal efficiency and the great difficulties related to handlingbiomass with high moisture and ash contents [22]

34 Pyrolysis and Gasification Products Characterization

341 Syngas Composition

(1) Pyrolysis Syngas Composition The syngas chemical com-position obtained throughout SS pyrolysis is shown in Fig-ure 5(a) The major gaseous products obtained from SSpyrolysis are CH4 (up to 1762) CO2 (up to 1203)H2 (up to 1085) CO (up to 726) and C119899H119898 (up to430) From Figure 5(a) it could be roughly seen that thevariation of several produced gases is almost constant witha high release at the beginning of the experiment (from300∘C) to achieve maximum of combustible gas productionat 600∘C and finally a gradual decrease marking the end ofthe pyrolysis reactions Among combustible gases CH4 andH2 are found to be the most abundant compounds of the

produced gases from SS pyrolysis The H2 high content inthe syngas mixture produced by pyrolysis could be explainedby the catalytic effect of the minerals contained in studiedSS (ash content around 3080) This catalytic effect in SSpyrolysis was highlighted by many authors [12 16] whostudied the correlation between the H2 percentage producedby pyrolysis of SS and the SS ash content and demonstratedthat the catalytic effect of the ash in the dehydrogenationreactions enhances the H2 production whereas the highH2 production is often correlated directly to the high ashcontent of SS which have a catalytic effect during thermalcracking and mainly in the dehydrogenation reactions [1216] Moreover the formation of CO and CO2 could beattributed to the decomposition of oxygenated groups suchas decarboxylation and decarbonylation [32] Other worksthat were conducted on SS pyrolysis have reported similar gascompositions Reference [12] presented a syngas compositionproduced from SS pyrolysis with a high yield (between 45and 66) of CO and H2 and reported that the gas fromthe conventional oven is much richer in hydrocarbons (25)than that from themicrowave ovens (6ndash11) According to [1]that studied SS flash pyrolysis in a conical spouted bed reactorat 600∘C the gas mixture composition is as follows 35 ofCO2 23 of CO 23 of H2 and 24 of C1ndashC4 Reference[16] obtained with the pyrolysis of three SS samples a gasmixture containing up to 60 of CO2 34 of CO 28 ofH2 11 of CH4 and 2-3 of C119899H119898

The calorific value (LHV) of the produced gas mixtureobtained under the pyrolysis conditions used in the presentstudy reaches a maximum of 996MJkg indicating a highcontent of combustible gases in this gaseous mixture Thisrelatively elevated heating value of the gas mixture can bevalorized as an alternative source of heating for the pyrolysisreactor The obtained heating values of gases are in the samerange as those reported by previous studies In fact the

10 BioMed Research International

heating values of gases from conventional pyrolysis were130ndash140MJm3 whereas with the microwave method theheating values ranged from 66 to 86MJm3 [11] Reference[33] that studied the pyrolysis of SS reported that the releasedgases have a maximum heating value around 25MJm3

(2) Gasification Syngas Composition The syngas chemicalcomposition analysis throughout the gasification experiment(Figure 5(b)) reveals that the obtained syngas is a mixtureof the following main components CO2 (up to 1843) CO(up to 76) H2 (up to 732) CH4 (up to 536) andC119899H119898 (up to 236) As can be observed in Figure 5(b)when the reactor temperature increased the CO and CO2concentrations increased due to decarbonylation and decar-boxylation reactions at high temperatures H2 concentrationincreased also with the temperature increase with a max-imum around 732wt at nearly 900∘C and this is due tonot only the cracking reactions but also dehydrogenationreactions promoted by the catalytic effect of the inorganicfraction [1 16] CH4 and C119899H119898 showed the same trendwith a slight variation from the beginning These drawndata are in agreement with those described by [2] where atypical gasification gaseousmixture is characterized by a highhydrogen content (H2 889ndash1117 vol) It contains also othercombustible compounds including CO (628ndash1077 vol)CH4 (126ndash209 vol) carbon dioxide and some light hydro-carbons Similar observations have been advanced by [17] thatstudied SS gasification using downdraft reactor and indicatedthat produced syngas is composed mainly of combustiblegases such as H2 (880ndash1115 vol) CO (631ndash1063 vol)CH4 (125ndash207 vol) and C119899H119898 (076ndash110 vol) and non-combustible gases such as N2 and CO2

The heating value of the syngas obtained under thegasification conditions used in the present study reachesa maximum of 802MJkg This calorific value is higherthan those reported for SS pyrolysis Reference [18] reportedgross heating values ranging from 487 to 555MJkg forsyngas produced from SS gasification in a downdraft gasifierwhereas [34] advanced LHV values ranging between 415 and709MJkg for syngas produced from two types of SS

342 Bio-Oil and Biochar Properties The bio-oil elementalcomposition is as follows C 5659wt H 824wt N396wt S 032 wt and O 3089wt The obtained car-bon hydrogen and sulphur contents are lower than thosefound by other authors from pyrolysis of SS Thus [34]obtained for bio-oils produced from conventional pyrolysisof SS carbon content between 709 and 845 wt hydrogencontent between 103 and 124 wt and sulphur contentbetween 02 and 06 wt Reference [33] reported for organicfraction of SS pyrolysis liquids between 494 and 626wtfor carbon and between 98 wt and 115 wt for hydrogennitrogen and sulphur contents are almost invariable [33 35]The knowledge of elemental composition (mainly carbonhydrogen and sulphur contents) is necessary for potentialutilization of these bio-oils as biofuels or for further process-ing to petrochemicals or biodiesel

The bio-oil density at 15∘C kinematic viscosity and watercontents of both organic and aqueous fractions from SS

Table 3 Fuel properties of liquid fractions obtained from SSpyrolysis (at 550∘C and 15∘Cmin)

Density (15∘C)(KgL)

Viscosity(40∘C)(mm2s)

Water content()

Organic fraction 09743 63 16Aqueousfraction 1 106 25

pyrolysis are reported in Table 3The organic fraction densityaround 09743Kgm3 is quite higher than those required bythe Tunisian standard fuels (between 820 and 860 kgm3)and also higher than those of similar bio-oils obtained fromdifferent feedstocks [27] The organic fraction viscosity isaround 63 cSt while the aqueous fraction one is about106 cSt these values are considerably higher than those of theTunisian standard fuels (45 cSt) and those of other bio-oilsreported in [27] The water content of the organic fraction isquite high (around 16) and this may be reduced with payingattention to the decantation of the two liquid phases

The FTIR spectrum of bio-oil sample obtained from SSpyrolysis is given in Figure 6(a)The liquid bio-oil seems to bevery complex mixture with a high content of aliphatic groupsindicated by the presence of intense peaks in the absorptionregion between 2800 and 3000 cmminus1 and several peaksbetween 1300 and 1500 cmminus1 imputable to aliphatic CndashHdeformation The aromatic character of the bio-oil sample ismarked by the peak around 1640 cmminus1 corresponding to C=Cin aromatic structures and by many little peaks in the regionbetween 700 and 900 cmminus1

The biochar sample spectrum (Figure 6(b)) shows highcontent of O-containing functions the band centred around3300 cmminus1 due to the presence of OndashH groups and the highintensive band between 1000 and 1100 cmminus1 correspondingto CndashO stretching of carbohydrate and alcohol functionsThe aliphatic groupsrsquo content is indicated mainly by the largebandbetween 1300 and 1500 cmminus1 imputable to aliphaticCndashHdeformation Usually the produced biochar obtained from SSpyrolysis could be used as biofuel (high calorific value) oras chemical adsorbent of pollutants (substitute for activatedcarbon) or as soil fertilizer [35] The potential use of biocharsin these three options depends on their characteristics

343 Gasification Coproducts Characterization Figures 6(c)and 6(d) show the FTIR spectra obtained from condensabletars and solid residue produced from gasification of predriedSS respectively The FTIR condensable tar spectrum showsthe high complexity of these productsThe studied tar sampleis composed of aliphatic compounds and aromatic and O-containing groups with a large variety of organic compoundsThe solid residue spectrum exhibits a slight absorption bandbetween 3200 and 3600 cmminus1 attributable to CndashO stretchingbut a very intensive peak around 1400 cmminus1 corresponding toaliphatic groups We note the presence of many little peaksin the absorption region of 700ndash900 cmminus1 imputable to thearomatic stretching vibrations

BioMed Research International 11

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

0616055050045040035030025020015010005000

minus005minus010minus015minus020

minus0239

C=CndashCHaromCndashO

A

ndashOHndashNH

ndashCH

ndashCH

ndashCH

(cＧminus1)

(a)

minus0123minus005

000005010015020025030035040045050055060065070075080085

0908

C=C CHarom

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

CndashO

A

ndashOHndashNH

ndashCH

(cＧminus1)

(b)

minus00800010203040506070809101112

127

C=C40

0

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHaromCndashO

A

ndashOHndashNH ndashCH

ndashCH

(cＧminus1)

(c)

minus0100001020304050607080910111213

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHarom

ndashOHndashNH

ndashCH

ndashCH

(d)

Figure 6 FTIR spectra of (a) bio-oil sample obtained by SS pyrolysis (b) biochar sample obtained by SS pyrolysis (c) tar sample obtainedby SS gasification and (d) solid residue sample obtained by SS gasification

35 Mathematical Modeling Stoichiometric Model

351 Pyrolysis Balance Equation (8) of pyrolysis is

C120572H120573O120574 + 119909H2Oyields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VO2(8)

120572 120573 and 120574 are determined by the elemental analysis119905 119906 119910 and 119911 are the number of moles of gas species

calculated in Section 353119899C 119899O and 119899H are calculated in Section 351119909 ldquothe number of moles of H2Ordquo is the difference

between the number of moles of oxygen in the products andthat contained in biomass 120574 and it is calculated as follows

119909 = 119910 + 2119911 + 2V + 119899O minus 120574 (in mol) (9)

119899 is the difference between the number of moles of carbonin the initial biomass and that contained in the obtainedproducts and it is calculated as follows

119899 = 120572 minus 119899C minus 119910 minus 119911 minus 119906 (in mol) (10)

119898 is the difference between the number of moles of hydrogenin the reactant and that in the products and is calculated asfollows

119898 = 120573 + 2119909 minus 2119905 minus 4119906 (in mol) (11)

352 Gasification Balance The reaction of gasification isdescribed as follows

C120572H120573O120574 + 119909 (O2 + 367N2)yields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(12)

120572 120573 120574 and 120575 are determined by the elemental analysis

12 BioMed Research International

Table 4 Raw material and syngas stoichiometric model calcula-tions

Element Number of moles

Raw material

Carbon 106Hydrogen 21556Oxygen 1673Nitrogen 322Sulfur 078

Syngas

Mg 41993 g119899N2

000119899O2

000119899CH4

462119899CO 109119899CO2

118119899H2

2286

119905 119906 119910 119911 119901 and 119902 are the number of moles of the gasspecies calculated in Section 353119909 ldquothe number of moles of airrdquo is the difference between

the number of moles of oxygen in the products and thatcontained in the biomass and is calculated as follows

2119909 = 2119902 + 119910 + 2119911 minus 119909 minus 120574 (in mol) (13)

The number of moles 119901 of nitrogen produced is calculated asfollows

119901 = 119909 lowast 376 (in mol) (14)

119899 is the difference between the number of moles of carboncontained in the initial biomass and that contained in theproducts and is calculated as follows

119899 = 120572 minus 119910 minus 119911 minus 119906 (in mol) (15)

119898 is the difference between the number of moles of dihydro-gen in the reactants and that contained in the products and iscalculated as follows

119898 = 120573 minus 2119905 minus 4119906 (in mol) (16)

353 Calculations Table 4 shows the raw material andsyngas stoichiometric model calculations Pyrolysis and gasi-fication balances are respectively illustrated by (17) and (19)

For Pyrolysis

C120572H120573O120574 + 119909H2O 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VHO2(17)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 and 119911 are the number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses data

According to data reported in Table 4 we obtain theglobal SS pyrolysis formula

C106H21556O1673 + 1326H2O 997888rarr

109CO + 118CO2 + 2286H2 + 462CH4

+ C29909H1247 + VHO2

(18)

For Gasification

C120572H120573O120574 + 119909 (O2 + 367N2) 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(19)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 119911 119901 and 119902 are number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses dataAccording to data reported in Table 4 we obtain the

global SS gasification formula

C106H21556O1673 + 127 (O2 + 367N2) 997888rarr

32CO + 68CO2 + 5977H2 + 23CH4

+ C12762H8648 + 467N2 + 047O2

(20)

The obtained pyrolysis and gasification formulas describeaverage degradation of SS compounds under pyrolysis andgasification circumstances The model calculations allow usto study the influence of process parameters and thus topredict the desired products yields

4 Conclusions

In this study pyrolysis and gasification of Tunisian solar driedSS were performed separately using two different laboratory-scale reactors to produce mainly hydrogen-rich syntheticgas Through this work we highlighted the opportunity ofemployment of these two processes in the conversion ofTunisian SS into combustible gases and thus the potential ofsolar dried SS wastes as feedstocks for syngas productionThe released gases from pyrolysis (yield reaching 23wt)and gasification (yield reaching 82wt) present high calorificvalues (around 996MJm3 for pyrolysis and 802MJkg forgasification) due to their high contents of H2 (up to 1085and 732 resp) and CH4 (up to 1762 and 536 resp)The produced syngas should be used either as a fuel or as anintermediate in the production of liquid fuels and chemicalsWe suggest its reuse to supply a part of the energy needed inthe heating part of the reactor in order to enhance the energybalance of the process

Taking into account these experimental and numericalresults it can be concluded that the SS energy recovery viapyrolysis and gasification is a viable method for reducing thevolume of these harmful products with producing valuableproducts and alternative fuels in order to reduce the con-sumption of fossil fuels

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

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Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

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Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

BioMed Research International 7

536

1311

8153

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Prod

ucts

yiel

ds (w

t)

TarsSolid residueSyngas

(a)

4030 39583095

3958

46934967

20121350

1938

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

10 15 20

Prod

ucts

yiel

ds (w

t)

Bio-oilBiocharSyngas

Heating rate (∘Cmin)

(b)

2739

4030

48465009 4809

2977

2247

1161

2177

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

500 550 600

Prod

ucts

yiel

ds (w

t)

Pyrolysis temperature (∘C)

Bio-oilBiocharSyngas

(c)

Figure 3 SS pyrolysis products distribution (a) variable pyrolysis temperature and invariable heating rate 15∘Cmin (b) variable heatingrate and invariable temperature 550∘C (c) SS gasification products distribution

and lignins leather some N-containing compounds such asaliphatic amino acids and aromatic compounds contained inplastic materials But due to the great heterogeneity of thestudied SS chemical composition it is difficult to attributethis decomposition to specific organic compounds After600∘C SS sample showed a weight loss of 316 of its originalmass attributed mainly to the decomposition of inorganicmaterials

32 Pyrolysis and Gasification Products Distribution Pyrol-ysis experimental conditions influence the products distri-bution and properties Among these parameters pyrolysisfinal temperature has the largest effect on the products yieldsThe pyrolysis temperature has been evaluated based on thethermogravimetric results and the previous studies of SSpyrolysis found in the literature Figure 3(a) exhibits theproducts (bio-oil biochar and syngas) distribution of SS

8 BioMed Research International

pyrolysis at different final temperatures (500 550 and 600∘C)and at an invariable heating rate (15∘Cmin) and a constantcooling temperature (minus5∘C) As it can be seen an increasein pyrolysis temperature (from 500 to 600∘C) results in adecrease in biochar yield (from 50 to 30) and an increasein liquid fraction yield (from 27 to 48) due probably to thepromotion of devolatilization reactions At higher tempera-tures secondary reactions involving volatiles such as thermalcracking are improved leading to a reduction in the liquidyield and an increase in the gas yieldThe decrease in biocharyield is possibly related also to further pyrolysis conversionand thus to a greater primary decomposition of the initialfeedstock or to secondary reactions of the solid residue [13]The syngas yield is variable in all conditions the pyrolysisgas amount is not very high (does not exceed 23) andthe optimum pyrolysis temperature obtained for maximumsyngas production is around 500∘CBy investigating the effectof reaction temperature (in the range of 450ndash600∘C) on theyields of SS pyrolysis products [1] obtained a maximum gasyield of 20 in dry and ash-free basis at 600∘C whereas [32]reported a maximum yield of gaseous products in the rangeof 15ndash25 at high temperature (700∘C) Reference [17] bystudying the influence of pyrolysis temperature on productsdistribution reported that gas yield remains almost constant(around 20ndash22) as the pyrolysis temperature increased from350 to 550∘C but above 550∘C a significant increase in gasproduction is observed (reaching a gas yield around 32)

Apart from temperature heating rate also plays a signif-icant role in products yields variation during SS pyrolysisFigure 3(b) shows the influence of heating rate variation onproducts yields distribution at an invariable final temperature(550∘C) and a constant cooling temperature (minus5∘C) It can beseen that an increase in the heating rate leads to a decreasein the liquid fraction and to an increase in the solid fractionwhile the gas fraction yield remains variableThese results arein agreement with the literature Reference [33] using twoheating rates (5∘Cmin and 60∘Cmin) demonstrated that theincrease in heating rate gives an increase in liquid productsyield and a decrease in biochar yield

Regarding the gasification process some operationalproblems were encountered in the measurement of productsyields such as (i) tars condensation and deposits duringcooling of the gasifier and at the outlet of the reactor and(ii) presence of tars in the produced syngas Roughly theobtained yields given in Figure 3(c) are as follows 82 ofsyngas 13 of solid residue and 5 of tars

33 Gasification Reactor Temperature Distribution In orderto distinguish the different zones within the gasificationreactor the temperature data recorded inside the gasifierwereexploited Figure 4 shows the inside reactor axial temperatureevolution obtained during the predried SS gasification expe-riences using five active thermocouples (from T1 to T5) Thetemperature curves recorded by thermocouples T1 (orangecolor) and T2 (green color) show a regular temperaturevariation around 50∘C until 100min from the beginningof the gasification experiment After that the temperatureincreased slowly for T1 and suddenly for T2 to reach 240∘Cand 290∘C respectively which were maintained until the

0

100

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000Time (sec)

T1 (∘C)

T2 (∘C)

T3 (∘C)

T4 (∘C)

T5 (∘C)

Tem

pera

ture

(∘C)

Figure 4 Reactor axial temperature evolution during solar dried SSgasification process

end of the experiment This corresponds to the drying zonein the reactor In this drying zone moisture content of thebiomass is reduced considerably The temperature variationsrecorded by thermocouples T3 (pink color) and T4 (bluecolor) show a regular evolution from room temperature toa maximum of 520∘C and by the end of the experimentto 750∘C as maximum temperature indicating the pyrolysisphase In this pyrolysis stage the thermal cracking of biomassoccurs in the absence of oxygen and solid residue (charcoal)and volatile vapors (containing carbon monoxide hydrogencarbon dioxide and hydrocarbon gases) are released [22]Thermocouple T5 (black color) recorded temperatures inthe gasification zone as it reaches rapidly high temperatureabove 900∘CThe gasification process of predried SS samplesstarted at moderate temperatures (between 600 and 700∘C)and achieves high temperatures (above 900∘C) at the end ofthe gasification experiment In this reduction area severalreactions occur and the temperature ranges between 800 and1000∘C These reactions are mostly endothermic in natureThe distribution of the gasifier axial temperature enables usto follow different mechanisms occurring throughout thegasification process and thus to delineate the different zoneswithin the reactor such us drying pyrolysis combustion andgasification Furthermore the temperature evolution showsthat the predried SS gasification reactions take place at hightemperature (above 900∘C) In this gasification area severalreduction reactions occur The main reactions in this zone asdescribed by [22] are as follows

Water-Gas Reaction

C +H2O 997888rarr CO +H2 Δ119867 = 1314 kJmol (4)

BioMed Research International 9

0

2

4

6

8

10

12

0102030405060708090

100

300 350 400 450 500 550 600 550 500 450 400 350 300

Calc

ulat

ed L

HV

(MJk

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2

（4

n（m

（2

2

(a)

0123456789

0102030405060708090

100

300 400 500 600 700 800 900 800 700 600 500

Calc

ulat

ed L

HV

(MJK

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2 2

（4

n（m

（2

2

(b)

Figure 5 Syngas chemical composition and LHV evolution during (a) SS pyrolysis process (600∘C and 20∘Cminminus1) and (b) SS gasificationprocess

Boudouard Reaction

C + CO2 997888rarr 2CO Δ119867 = 1726 kJmol (5)

Shift Reaction

CO2 +H2 997888rarr CO +H2O Δ119867 = 42 kJmol (6)

Methane Reaction

C + 2H2 997888rarr CH4 Δ119867 = 75 kJmol (7)

In total the fixed-bed downdraft gasifier is recommendedequipment to study the gasification reactions and mecha-nisms at laboratory scale and to produce clean gas but themain disadvantages of this type of gasifier are its low ther-mal efficiency and the great difficulties related to handlingbiomass with high moisture and ash contents [22]

34 Pyrolysis and Gasification Products Characterization

341 Syngas Composition

(1) Pyrolysis Syngas Composition The syngas chemical com-position obtained throughout SS pyrolysis is shown in Fig-ure 5(a) The major gaseous products obtained from SSpyrolysis are CH4 (up to 1762) CO2 (up to 1203)H2 (up to 1085) CO (up to 726) and C119899H119898 (up to430) From Figure 5(a) it could be roughly seen that thevariation of several produced gases is almost constant witha high release at the beginning of the experiment (from300∘C) to achieve maximum of combustible gas productionat 600∘C and finally a gradual decrease marking the end ofthe pyrolysis reactions Among combustible gases CH4 andH2 are found to be the most abundant compounds of the

produced gases from SS pyrolysis The H2 high content inthe syngas mixture produced by pyrolysis could be explainedby the catalytic effect of the minerals contained in studiedSS (ash content around 3080) This catalytic effect in SSpyrolysis was highlighted by many authors [12 16] whostudied the correlation between the H2 percentage producedby pyrolysis of SS and the SS ash content and demonstratedthat the catalytic effect of the ash in the dehydrogenationreactions enhances the H2 production whereas the highH2 production is often correlated directly to the high ashcontent of SS which have a catalytic effect during thermalcracking and mainly in the dehydrogenation reactions [1216] Moreover the formation of CO and CO2 could beattributed to the decomposition of oxygenated groups suchas decarboxylation and decarbonylation [32] Other worksthat were conducted on SS pyrolysis have reported similar gascompositions Reference [12] presented a syngas compositionproduced from SS pyrolysis with a high yield (between 45and 66) of CO and H2 and reported that the gas fromthe conventional oven is much richer in hydrocarbons (25)than that from themicrowave ovens (6ndash11) According to [1]that studied SS flash pyrolysis in a conical spouted bed reactorat 600∘C the gas mixture composition is as follows 35 ofCO2 23 of CO 23 of H2 and 24 of C1ndashC4 Reference[16] obtained with the pyrolysis of three SS samples a gasmixture containing up to 60 of CO2 34 of CO 28 ofH2 11 of CH4 and 2-3 of C119899H119898

The calorific value (LHV) of the produced gas mixtureobtained under the pyrolysis conditions used in the presentstudy reaches a maximum of 996MJkg indicating a highcontent of combustible gases in this gaseous mixture Thisrelatively elevated heating value of the gas mixture can bevalorized as an alternative source of heating for the pyrolysisreactor The obtained heating values of gases are in the samerange as those reported by previous studies In fact the

10 BioMed Research International

heating values of gases from conventional pyrolysis were130ndash140MJm3 whereas with the microwave method theheating values ranged from 66 to 86MJm3 [11] Reference[33] that studied the pyrolysis of SS reported that the releasedgases have a maximum heating value around 25MJm3

(2) Gasification Syngas Composition The syngas chemicalcomposition analysis throughout the gasification experiment(Figure 5(b)) reveals that the obtained syngas is a mixtureof the following main components CO2 (up to 1843) CO(up to 76) H2 (up to 732) CH4 (up to 536) andC119899H119898 (up to 236) As can be observed in Figure 5(b)when the reactor temperature increased the CO and CO2concentrations increased due to decarbonylation and decar-boxylation reactions at high temperatures H2 concentrationincreased also with the temperature increase with a max-imum around 732wt at nearly 900∘C and this is due tonot only the cracking reactions but also dehydrogenationreactions promoted by the catalytic effect of the inorganicfraction [1 16] CH4 and C119899H119898 showed the same trendwith a slight variation from the beginning These drawndata are in agreement with those described by [2] where atypical gasification gaseousmixture is characterized by a highhydrogen content (H2 889ndash1117 vol) It contains also othercombustible compounds including CO (628ndash1077 vol)CH4 (126ndash209 vol) carbon dioxide and some light hydro-carbons Similar observations have been advanced by [17] thatstudied SS gasification using downdraft reactor and indicatedthat produced syngas is composed mainly of combustiblegases such as H2 (880ndash1115 vol) CO (631ndash1063 vol)CH4 (125ndash207 vol) and C119899H119898 (076ndash110 vol) and non-combustible gases such as N2 and CO2

The heating value of the syngas obtained under thegasification conditions used in the present study reachesa maximum of 802MJkg This calorific value is higherthan those reported for SS pyrolysis Reference [18] reportedgross heating values ranging from 487 to 555MJkg forsyngas produced from SS gasification in a downdraft gasifierwhereas [34] advanced LHV values ranging between 415 and709MJkg for syngas produced from two types of SS

342 Bio-Oil and Biochar Properties The bio-oil elementalcomposition is as follows C 5659wt H 824wt N396wt S 032 wt and O 3089wt The obtained car-bon hydrogen and sulphur contents are lower than thosefound by other authors from pyrolysis of SS Thus [34]obtained for bio-oils produced from conventional pyrolysisof SS carbon content between 709 and 845 wt hydrogencontent between 103 and 124 wt and sulphur contentbetween 02 and 06 wt Reference [33] reported for organicfraction of SS pyrolysis liquids between 494 and 626wtfor carbon and between 98 wt and 115 wt for hydrogennitrogen and sulphur contents are almost invariable [33 35]The knowledge of elemental composition (mainly carbonhydrogen and sulphur contents) is necessary for potentialutilization of these bio-oils as biofuels or for further process-ing to petrochemicals or biodiesel

The bio-oil density at 15∘C kinematic viscosity and watercontents of both organic and aqueous fractions from SS

Table 3 Fuel properties of liquid fractions obtained from SSpyrolysis (at 550∘C and 15∘Cmin)

Density (15∘C)(KgL)

Viscosity(40∘C)(mm2s)

Water content()

Organic fraction 09743 63 16Aqueousfraction 1 106 25

pyrolysis are reported in Table 3The organic fraction densityaround 09743Kgm3 is quite higher than those required bythe Tunisian standard fuels (between 820 and 860 kgm3)and also higher than those of similar bio-oils obtained fromdifferent feedstocks [27] The organic fraction viscosity isaround 63 cSt while the aqueous fraction one is about106 cSt these values are considerably higher than those of theTunisian standard fuels (45 cSt) and those of other bio-oilsreported in [27] The water content of the organic fraction isquite high (around 16) and this may be reduced with payingattention to the decantation of the two liquid phases

The FTIR spectrum of bio-oil sample obtained from SSpyrolysis is given in Figure 6(a)The liquid bio-oil seems to bevery complex mixture with a high content of aliphatic groupsindicated by the presence of intense peaks in the absorptionregion between 2800 and 3000 cmminus1 and several peaksbetween 1300 and 1500 cmminus1 imputable to aliphatic CndashHdeformation The aromatic character of the bio-oil sample ismarked by the peak around 1640 cmminus1 corresponding to C=Cin aromatic structures and by many little peaks in the regionbetween 700 and 900 cmminus1

The biochar sample spectrum (Figure 6(b)) shows highcontent of O-containing functions the band centred around3300 cmminus1 due to the presence of OndashH groups and the highintensive band between 1000 and 1100 cmminus1 correspondingto CndashO stretching of carbohydrate and alcohol functionsThe aliphatic groupsrsquo content is indicated mainly by the largebandbetween 1300 and 1500 cmminus1 imputable to aliphaticCndashHdeformation Usually the produced biochar obtained from SSpyrolysis could be used as biofuel (high calorific value) oras chemical adsorbent of pollutants (substitute for activatedcarbon) or as soil fertilizer [35] The potential use of biocharsin these three options depends on their characteristics

343 Gasification Coproducts Characterization Figures 6(c)and 6(d) show the FTIR spectra obtained from condensabletars and solid residue produced from gasification of predriedSS respectively The FTIR condensable tar spectrum showsthe high complexity of these productsThe studied tar sampleis composed of aliphatic compounds and aromatic and O-containing groups with a large variety of organic compoundsThe solid residue spectrum exhibits a slight absorption bandbetween 3200 and 3600 cmminus1 attributable to CndashO stretchingbut a very intensive peak around 1400 cmminus1 corresponding toaliphatic groups We note the presence of many little peaksin the absorption region of 700ndash900 cmminus1 imputable to thearomatic stretching vibrations

BioMed Research International 11

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

0616055050045040035030025020015010005000

minus005minus010minus015minus020

minus0239

C=CndashCHaromCndashO

A

ndashOHndashNH

ndashCH

ndashCH

ndashCH

(cＧminus1)

(a)

minus0123minus005

000005010015020025030035040045050055060065070075080085

0908

C=C CHarom

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

CndashO

A

ndashOHndashNH

ndashCH

(cＧminus1)

(b)

minus00800010203040506070809101112

127

C=C40

0

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHaromCndashO

A

ndashOHndashNH ndashCH

ndashCH

(cＧminus1)

(c)

minus0100001020304050607080910111213

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHarom

ndashOHndashNH

ndashCH

ndashCH

(d)

Figure 6 FTIR spectra of (a) bio-oil sample obtained by SS pyrolysis (b) biochar sample obtained by SS pyrolysis (c) tar sample obtainedby SS gasification and (d) solid residue sample obtained by SS gasification

35 Mathematical Modeling Stoichiometric Model

351 Pyrolysis Balance Equation (8) of pyrolysis is

C120572H120573O120574 + 119909H2Oyields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VO2(8)

120572 120573 and 120574 are determined by the elemental analysis119905 119906 119910 and 119911 are the number of moles of gas species

calculated in Section 353119899C 119899O and 119899H are calculated in Section 351119909 ldquothe number of moles of H2Ordquo is the difference

between the number of moles of oxygen in the products andthat contained in biomass 120574 and it is calculated as follows

119909 = 119910 + 2119911 + 2V + 119899O minus 120574 (in mol) (9)

119899 is the difference between the number of moles of carbonin the initial biomass and that contained in the obtainedproducts and it is calculated as follows

119899 = 120572 minus 119899C minus 119910 minus 119911 minus 119906 (in mol) (10)

119898 is the difference between the number of moles of hydrogenin the reactant and that in the products and is calculated asfollows

119898 = 120573 + 2119909 minus 2119905 minus 4119906 (in mol) (11)

352 Gasification Balance The reaction of gasification isdescribed as follows

C120572H120573O120574 + 119909 (O2 + 367N2)yields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(12)

120572 120573 120574 and 120575 are determined by the elemental analysis

12 BioMed Research International

Table 4 Raw material and syngas stoichiometric model calcula-tions

Element Number of moles

Raw material

Carbon 106Hydrogen 21556Oxygen 1673Nitrogen 322Sulfur 078

Syngas

Mg 41993 g119899N2

000119899O2

000119899CH4

462119899CO 109119899CO2

118119899H2

2286

119905 119906 119910 119911 119901 and 119902 are the number of moles of the gasspecies calculated in Section 353119909 ldquothe number of moles of airrdquo is the difference between

the number of moles of oxygen in the products and thatcontained in the biomass and is calculated as follows

2119909 = 2119902 + 119910 + 2119911 minus 119909 minus 120574 (in mol) (13)

The number of moles 119901 of nitrogen produced is calculated asfollows

119901 = 119909 lowast 376 (in mol) (14)

119899 is the difference between the number of moles of carboncontained in the initial biomass and that contained in theproducts and is calculated as follows

119899 = 120572 minus 119910 minus 119911 minus 119906 (in mol) (15)

119898 is the difference between the number of moles of dihydro-gen in the reactants and that contained in the products and iscalculated as follows

119898 = 120573 minus 2119905 minus 4119906 (in mol) (16)

353 Calculations Table 4 shows the raw material andsyngas stoichiometric model calculations Pyrolysis and gasi-fication balances are respectively illustrated by (17) and (19)

For Pyrolysis

C120572H120573O120574 + 119909H2O 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VHO2(17)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 and 119911 are the number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses data

According to data reported in Table 4 we obtain theglobal SS pyrolysis formula

C106H21556O1673 + 1326H2O 997888rarr

109CO + 118CO2 + 2286H2 + 462CH4

+ C29909H1247 + VHO2

(18)

For Gasification

C120572H120573O120574 + 119909 (O2 + 367N2) 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(19)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 119911 119901 and 119902 are number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses dataAccording to data reported in Table 4 we obtain the

global SS gasification formula

C106H21556O1673 + 127 (O2 + 367N2) 997888rarr

32CO + 68CO2 + 5977H2 + 23CH4

+ C12762H8648 + 467N2 + 047O2

(20)

The obtained pyrolysis and gasification formulas describeaverage degradation of SS compounds under pyrolysis andgasification circumstances The model calculations allow usto study the influence of process parameters and thus topredict the desired products yields

4 Conclusions

In this study pyrolysis and gasification of Tunisian solar driedSS were performed separately using two different laboratory-scale reactors to produce mainly hydrogen-rich syntheticgas Through this work we highlighted the opportunity ofemployment of these two processes in the conversion ofTunisian SS into combustible gases and thus the potential ofsolar dried SS wastes as feedstocks for syngas productionThe released gases from pyrolysis (yield reaching 23wt)and gasification (yield reaching 82wt) present high calorificvalues (around 996MJm3 for pyrolysis and 802MJkg forgasification) due to their high contents of H2 (up to 1085and 732 resp) and CH4 (up to 1762 and 536 resp)The produced syngas should be used either as a fuel or as anintermediate in the production of liquid fuels and chemicalsWe suggest its reuse to supply a part of the energy needed inthe heating part of the reactor in order to enhance the energybalance of the process

Taking into account these experimental and numericalresults it can be concluded that the SS energy recovery viapyrolysis and gasification is a viable method for reducing thevolume of these harmful products with producing valuableproducts and alternative fuels in order to reduce the con-sumption of fossil fuels

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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International Journal of

Volume 201

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GenomicsInternational Journal of

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Signal TransductionJournal of

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Evolutionary BiologyInternational Journal of

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ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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International Journal of

Microbiology

8 BioMed Research International

pyrolysis at different final temperatures (500 550 and 600∘C)and at an invariable heating rate (15∘Cmin) and a constantcooling temperature (minus5∘C) As it can be seen an increasein pyrolysis temperature (from 500 to 600∘C) results in adecrease in biochar yield (from 50 to 30) and an increasein liquid fraction yield (from 27 to 48) due probably to thepromotion of devolatilization reactions At higher tempera-tures secondary reactions involving volatiles such as thermalcracking are improved leading to a reduction in the liquidyield and an increase in the gas yieldThe decrease in biocharyield is possibly related also to further pyrolysis conversionand thus to a greater primary decomposition of the initialfeedstock or to secondary reactions of the solid residue [13]The syngas yield is variable in all conditions the pyrolysisgas amount is not very high (does not exceed 23) andthe optimum pyrolysis temperature obtained for maximumsyngas production is around 500∘CBy investigating the effectof reaction temperature (in the range of 450ndash600∘C) on theyields of SS pyrolysis products [1] obtained a maximum gasyield of 20 in dry and ash-free basis at 600∘C whereas [32]reported a maximum yield of gaseous products in the rangeof 15ndash25 at high temperature (700∘C) Reference [17] bystudying the influence of pyrolysis temperature on productsdistribution reported that gas yield remains almost constant(around 20ndash22) as the pyrolysis temperature increased from350 to 550∘C but above 550∘C a significant increase in gasproduction is observed (reaching a gas yield around 32)

Apart from temperature heating rate also plays a signif-icant role in products yields variation during SS pyrolysisFigure 3(b) shows the influence of heating rate variation onproducts yields distribution at an invariable final temperature(550∘C) and a constant cooling temperature (minus5∘C) It can beseen that an increase in the heating rate leads to a decreasein the liquid fraction and to an increase in the solid fractionwhile the gas fraction yield remains variableThese results arein agreement with the literature Reference [33] using twoheating rates (5∘Cmin and 60∘Cmin) demonstrated that theincrease in heating rate gives an increase in liquid productsyield and a decrease in biochar yield

Regarding the gasification process some operationalproblems were encountered in the measurement of productsyields such as (i) tars condensation and deposits duringcooling of the gasifier and at the outlet of the reactor and(ii) presence of tars in the produced syngas Roughly theobtained yields given in Figure 3(c) are as follows 82 ofsyngas 13 of solid residue and 5 of tars

33 Gasification Reactor Temperature Distribution In orderto distinguish the different zones within the gasificationreactor the temperature data recorded inside the gasifierwereexploited Figure 4 shows the inside reactor axial temperatureevolution obtained during the predried SS gasification expe-riences using five active thermocouples (from T1 to T5) Thetemperature curves recorded by thermocouples T1 (orangecolor) and T2 (green color) show a regular temperaturevariation around 50∘C until 100min from the beginningof the gasification experiment After that the temperatureincreased slowly for T1 and suddenly for T2 to reach 240∘Cand 290∘C respectively which were maintained until the

0

100

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000Time (sec)

T1 (∘C)

T2 (∘C)

T3 (∘C)

T4 (∘C)

T5 (∘C)

Tem

pera

ture

(∘C)

Figure 4 Reactor axial temperature evolution during solar dried SSgasification process

end of the experiment This corresponds to the drying zonein the reactor In this drying zone moisture content of thebiomass is reduced considerably The temperature variationsrecorded by thermocouples T3 (pink color) and T4 (bluecolor) show a regular evolution from room temperature toa maximum of 520∘C and by the end of the experimentto 750∘C as maximum temperature indicating the pyrolysisphase In this pyrolysis stage the thermal cracking of biomassoccurs in the absence of oxygen and solid residue (charcoal)and volatile vapors (containing carbon monoxide hydrogencarbon dioxide and hydrocarbon gases) are released [22]Thermocouple T5 (black color) recorded temperatures inthe gasification zone as it reaches rapidly high temperatureabove 900∘CThe gasification process of predried SS samplesstarted at moderate temperatures (between 600 and 700∘C)and achieves high temperatures (above 900∘C) at the end ofthe gasification experiment In this reduction area severalreactions occur and the temperature ranges between 800 and1000∘C These reactions are mostly endothermic in natureThe distribution of the gasifier axial temperature enables usto follow different mechanisms occurring throughout thegasification process and thus to delineate the different zoneswithin the reactor such us drying pyrolysis combustion andgasification Furthermore the temperature evolution showsthat the predried SS gasification reactions take place at hightemperature (above 900∘C) In this gasification area severalreduction reactions occur The main reactions in this zone asdescribed by [22] are as follows

Water-Gas Reaction

C +H2O 997888rarr CO +H2 Δ119867 = 1314 kJmol (4)

BioMed Research International 9

0

2

4

6

8

10

12

0102030405060708090

100

300 350 400 450 500 550 600 550 500 450 400 350 300

Calc

ulat

ed L

HV

(MJk

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2

（4

n（m

（2

2

(a)

0123456789

0102030405060708090

100

300 400 500 600 700 800 900 800 700 600 500

Calc

ulat

ed L

HV

(MJK

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2 2

（4

n（m

（2

2

(b)

Figure 5 Syngas chemical composition and LHV evolution during (a) SS pyrolysis process (600∘C and 20∘Cminminus1) and (b) SS gasificationprocess

Boudouard Reaction

C + CO2 997888rarr 2CO Δ119867 = 1726 kJmol (5)

Shift Reaction

CO2 +H2 997888rarr CO +H2O Δ119867 = 42 kJmol (6)

Methane Reaction

C + 2H2 997888rarr CH4 Δ119867 = 75 kJmol (7)

In total the fixed-bed downdraft gasifier is recommendedequipment to study the gasification reactions and mecha-nisms at laboratory scale and to produce clean gas but themain disadvantages of this type of gasifier are its low ther-mal efficiency and the great difficulties related to handlingbiomass with high moisture and ash contents [22]

34 Pyrolysis and Gasification Products Characterization

341 Syngas Composition

(1) Pyrolysis Syngas Composition The syngas chemical com-position obtained throughout SS pyrolysis is shown in Fig-ure 5(a) The major gaseous products obtained from SSpyrolysis are CH4 (up to 1762) CO2 (up to 1203)H2 (up to 1085) CO (up to 726) and C119899H119898 (up to430) From Figure 5(a) it could be roughly seen that thevariation of several produced gases is almost constant witha high release at the beginning of the experiment (from300∘C) to achieve maximum of combustible gas productionat 600∘C and finally a gradual decrease marking the end ofthe pyrolysis reactions Among combustible gases CH4 andH2 are found to be the most abundant compounds of the

produced gases from SS pyrolysis The H2 high content inthe syngas mixture produced by pyrolysis could be explainedby the catalytic effect of the minerals contained in studiedSS (ash content around 3080) This catalytic effect in SSpyrolysis was highlighted by many authors [12 16] whostudied the correlation between the H2 percentage producedby pyrolysis of SS and the SS ash content and demonstratedthat the catalytic effect of the ash in the dehydrogenationreactions enhances the H2 production whereas the highH2 production is often correlated directly to the high ashcontent of SS which have a catalytic effect during thermalcracking and mainly in the dehydrogenation reactions [1216] Moreover the formation of CO and CO2 could beattributed to the decomposition of oxygenated groups suchas decarboxylation and decarbonylation [32] Other worksthat were conducted on SS pyrolysis have reported similar gascompositions Reference [12] presented a syngas compositionproduced from SS pyrolysis with a high yield (between 45and 66) of CO and H2 and reported that the gas fromthe conventional oven is much richer in hydrocarbons (25)than that from themicrowave ovens (6ndash11) According to [1]that studied SS flash pyrolysis in a conical spouted bed reactorat 600∘C the gas mixture composition is as follows 35 ofCO2 23 of CO 23 of H2 and 24 of C1ndashC4 Reference[16] obtained with the pyrolysis of three SS samples a gasmixture containing up to 60 of CO2 34 of CO 28 ofH2 11 of CH4 and 2-3 of C119899H119898

The calorific value (LHV) of the produced gas mixtureobtained under the pyrolysis conditions used in the presentstudy reaches a maximum of 996MJkg indicating a highcontent of combustible gases in this gaseous mixture Thisrelatively elevated heating value of the gas mixture can bevalorized as an alternative source of heating for the pyrolysisreactor The obtained heating values of gases are in the samerange as those reported by previous studies In fact the

10 BioMed Research International

heating values of gases from conventional pyrolysis were130ndash140MJm3 whereas with the microwave method theheating values ranged from 66 to 86MJm3 [11] Reference[33] that studied the pyrolysis of SS reported that the releasedgases have a maximum heating value around 25MJm3

(2) Gasification Syngas Composition The syngas chemicalcomposition analysis throughout the gasification experiment(Figure 5(b)) reveals that the obtained syngas is a mixtureof the following main components CO2 (up to 1843) CO(up to 76) H2 (up to 732) CH4 (up to 536) andC119899H119898 (up to 236) As can be observed in Figure 5(b)when the reactor temperature increased the CO and CO2concentrations increased due to decarbonylation and decar-boxylation reactions at high temperatures H2 concentrationincreased also with the temperature increase with a max-imum around 732wt at nearly 900∘C and this is due tonot only the cracking reactions but also dehydrogenationreactions promoted by the catalytic effect of the inorganicfraction [1 16] CH4 and C119899H119898 showed the same trendwith a slight variation from the beginning These drawndata are in agreement with those described by [2] where atypical gasification gaseousmixture is characterized by a highhydrogen content (H2 889ndash1117 vol) It contains also othercombustible compounds including CO (628ndash1077 vol)CH4 (126ndash209 vol) carbon dioxide and some light hydro-carbons Similar observations have been advanced by [17] thatstudied SS gasification using downdraft reactor and indicatedthat produced syngas is composed mainly of combustiblegases such as H2 (880ndash1115 vol) CO (631ndash1063 vol)CH4 (125ndash207 vol) and C119899H119898 (076ndash110 vol) and non-combustible gases such as N2 and CO2

The heating value of the syngas obtained under thegasification conditions used in the present study reachesa maximum of 802MJkg This calorific value is higherthan those reported for SS pyrolysis Reference [18] reportedgross heating values ranging from 487 to 555MJkg forsyngas produced from SS gasification in a downdraft gasifierwhereas [34] advanced LHV values ranging between 415 and709MJkg for syngas produced from two types of SS

342 Bio-Oil and Biochar Properties The bio-oil elementalcomposition is as follows C 5659wt H 824wt N396wt S 032 wt and O 3089wt The obtained car-bon hydrogen and sulphur contents are lower than thosefound by other authors from pyrolysis of SS Thus [34]obtained for bio-oils produced from conventional pyrolysisof SS carbon content between 709 and 845 wt hydrogencontent between 103 and 124 wt and sulphur contentbetween 02 and 06 wt Reference [33] reported for organicfraction of SS pyrolysis liquids between 494 and 626wtfor carbon and between 98 wt and 115 wt for hydrogennitrogen and sulphur contents are almost invariable [33 35]The knowledge of elemental composition (mainly carbonhydrogen and sulphur contents) is necessary for potentialutilization of these bio-oils as biofuels or for further process-ing to petrochemicals or biodiesel

The bio-oil density at 15∘C kinematic viscosity and watercontents of both organic and aqueous fractions from SS

Table 3 Fuel properties of liquid fractions obtained from SSpyrolysis (at 550∘C and 15∘Cmin)

Density (15∘C)(KgL)

Viscosity(40∘C)(mm2s)

Water content()

Organic fraction 09743 63 16Aqueousfraction 1 106 25

pyrolysis are reported in Table 3The organic fraction densityaround 09743Kgm3 is quite higher than those required bythe Tunisian standard fuels (between 820 and 860 kgm3)and also higher than those of similar bio-oils obtained fromdifferent feedstocks [27] The organic fraction viscosity isaround 63 cSt while the aqueous fraction one is about106 cSt these values are considerably higher than those of theTunisian standard fuels (45 cSt) and those of other bio-oilsreported in [27] The water content of the organic fraction isquite high (around 16) and this may be reduced with payingattention to the decantation of the two liquid phases

The FTIR spectrum of bio-oil sample obtained from SSpyrolysis is given in Figure 6(a)The liquid bio-oil seems to bevery complex mixture with a high content of aliphatic groupsindicated by the presence of intense peaks in the absorptionregion between 2800 and 3000 cmminus1 and several peaksbetween 1300 and 1500 cmminus1 imputable to aliphatic CndashHdeformation The aromatic character of the bio-oil sample ismarked by the peak around 1640 cmminus1 corresponding to C=Cin aromatic structures and by many little peaks in the regionbetween 700 and 900 cmminus1

The biochar sample spectrum (Figure 6(b)) shows highcontent of O-containing functions the band centred around3300 cmminus1 due to the presence of OndashH groups and the highintensive band between 1000 and 1100 cmminus1 correspondingto CndashO stretching of carbohydrate and alcohol functionsThe aliphatic groupsrsquo content is indicated mainly by the largebandbetween 1300 and 1500 cmminus1 imputable to aliphaticCndashHdeformation Usually the produced biochar obtained from SSpyrolysis could be used as biofuel (high calorific value) oras chemical adsorbent of pollutants (substitute for activatedcarbon) or as soil fertilizer [35] The potential use of biocharsin these three options depends on their characteristics

343 Gasification Coproducts Characterization Figures 6(c)and 6(d) show the FTIR spectra obtained from condensabletars and solid residue produced from gasification of predriedSS respectively The FTIR condensable tar spectrum showsthe high complexity of these productsThe studied tar sampleis composed of aliphatic compounds and aromatic and O-containing groups with a large variety of organic compoundsThe solid residue spectrum exhibits a slight absorption bandbetween 3200 and 3600 cmminus1 attributable to CndashO stretchingbut a very intensive peak around 1400 cmminus1 corresponding toaliphatic groups We note the presence of many little peaksin the absorption region of 700ndash900 cmminus1 imputable to thearomatic stretching vibrations

BioMed Research International 11

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

0616055050045040035030025020015010005000

minus005minus010minus015minus020

minus0239

C=CndashCHaromCndashO

A

ndashOHndashNH

ndashCH

ndashCH

ndashCH

(cＧminus1)

(a)

minus0123minus005

000005010015020025030035040045050055060065070075080085

0908

C=C CHarom

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

CndashO

A

ndashOHndashNH

ndashCH

(cＧminus1)

(b)

minus00800010203040506070809101112

127

C=C40

0

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHaromCndashO

A

ndashOHndashNH ndashCH

ndashCH

(cＧminus1)

(c)

minus0100001020304050607080910111213

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHarom

ndashOHndashNH

ndashCH

ndashCH

(d)

Figure 6 FTIR spectra of (a) bio-oil sample obtained by SS pyrolysis (b) biochar sample obtained by SS pyrolysis (c) tar sample obtainedby SS gasification and (d) solid residue sample obtained by SS gasification

35 Mathematical Modeling Stoichiometric Model

351 Pyrolysis Balance Equation (8) of pyrolysis is

C120572H120573O120574 + 119909H2Oyields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VO2(8)

120572 120573 and 120574 are determined by the elemental analysis119905 119906 119910 and 119911 are the number of moles of gas species

calculated in Section 353119899C 119899O and 119899H are calculated in Section 351119909 ldquothe number of moles of H2Ordquo is the difference

between the number of moles of oxygen in the products andthat contained in biomass 120574 and it is calculated as follows

119909 = 119910 + 2119911 + 2V + 119899O minus 120574 (in mol) (9)

119899 is the difference between the number of moles of carbonin the initial biomass and that contained in the obtainedproducts and it is calculated as follows

119899 = 120572 minus 119899C minus 119910 minus 119911 minus 119906 (in mol) (10)

119898 is the difference between the number of moles of hydrogenin the reactant and that in the products and is calculated asfollows

119898 = 120573 + 2119909 minus 2119905 minus 4119906 (in mol) (11)

352 Gasification Balance The reaction of gasification isdescribed as follows

C120572H120573O120574 + 119909 (O2 + 367N2)yields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(12)

120572 120573 120574 and 120575 are determined by the elemental analysis

12 BioMed Research International

Table 4 Raw material and syngas stoichiometric model calcula-tions

Element Number of moles

Raw material

Carbon 106Hydrogen 21556Oxygen 1673Nitrogen 322Sulfur 078

Syngas

Mg 41993 g119899N2

000119899O2

000119899CH4

462119899CO 109119899CO2

118119899H2

2286

119905 119906 119910 119911 119901 and 119902 are the number of moles of the gasspecies calculated in Section 353119909 ldquothe number of moles of airrdquo is the difference between

the number of moles of oxygen in the products and thatcontained in the biomass and is calculated as follows

2119909 = 2119902 + 119910 + 2119911 minus 119909 minus 120574 (in mol) (13)

The number of moles 119901 of nitrogen produced is calculated asfollows

119901 = 119909 lowast 376 (in mol) (14)

119899 is the difference between the number of moles of carboncontained in the initial biomass and that contained in theproducts and is calculated as follows

119899 = 120572 minus 119910 minus 119911 minus 119906 (in mol) (15)

119898 is the difference between the number of moles of dihydro-gen in the reactants and that contained in the products and iscalculated as follows

119898 = 120573 minus 2119905 minus 4119906 (in mol) (16)

353 Calculations Table 4 shows the raw material andsyngas stoichiometric model calculations Pyrolysis and gasi-fication balances are respectively illustrated by (17) and (19)

For Pyrolysis

C120572H120573O120574 + 119909H2O 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VHO2(17)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 and 119911 are the number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses data

According to data reported in Table 4 we obtain theglobal SS pyrolysis formula

C106H21556O1673 + 1326H2O 997888rarr

109CO + 118CO2 + 2286H2 + 462CH4

+ C29909H1247 + VHO2

(18)

For Gasification

C120572H120573O120574 + 119909 (O2 + 367N2) 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(19)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 119911 119901 and 119902 are number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses dataAccording to data reported in Table 4 we obtain the

global SS gasification formula

C106H21556O1673 + 127 (O2 + 367N2) 997888rarr

32CO + 68CO2 + 5977H2 + 23CH4

+ C12762H8648 + 467N2 + 047O2

(20)

The obtained pyrolysis and gasification formulas describeaverage degradation of SS compounds under pyrolysis andgasification circumstances The model calculations allow usto study the influence of process parameters and thus topredict the desired products yields

4 Conclusions

In this study pyrolysis and gasification of Tunisian solar driedSS were performed separately using two different laboratory-scale reactors to produce mainly hydrogen-rich syntheticgas Through this work we highlighted the opportunity ofemployment of these two processes in the conversion ofTunisian SS into combustible gases and thus the potential ofsolar dried SS wastes as feedstocks for syngas productionThe released gases from pyrolysis (yield reaching 23wt)and gasification (yield reaching 82wt) present high calorificvalues (around 996MJm3 for pyrolysis and 802MJkg forgasification) due to their high contents of H2 (up to 1085and 732 resp) and CH4 (up to 1762 and 536 resp)The produced syngas should be used either as a fuel or as anintermediate in the production of liquid fuels and chemicalsWe suggest its reuse to supply a part of the energy needed inthe heating part of the reactor in order to enhance the energybalance of the process

Taking into account these experimental and numericalresults it can be concluded that the SS energy recovery viapyrolysis and gasification is a viable method for reducing thevolume of these harmful products with producing valuableproducts and alternative fuels in order to reduce the con-sumption of fossil fuels

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

BioMed Research International 9

0

2

4

6

8

10

12

0102030405060708090

100

300 350 400 450 500 550 600 550 500 450 400 350 300

Calc

ulat

ed L

HV

(MJk

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2

（4

n（m

（2

2

(a)

0123456789

0102030405060708090

100

300 400 500 600 700 800 900 800 700 600 500

Calc

ulat

ed L

HV

(MJK

g)

Syng

as co

mpo

sitio

n (

)

CO

Calculated LHV

Temperature (∘C)

2 2

（4

n（m

（2

2

(b)

Figure 5 Syngas chemical composition and LHV evolution during (a) SS pyrolysis process (600∘C and 20∘Cminminus1) and (b) SS gasificationprocess

Boudouard Reaction

C + CO2 997888rarr 2CO Δ119867 = 1726 kJmol (5)

Shift Reaction

CO2 +H2 997888rarr CO +H2O Δ119867 = 42 kJmol (6)

Methane Reaction

C + 2H2 997888rarr CH4 Δ119867 = 75 kJmol (7)

In total the fixed-bed downdraft gasifier is recommendedequipment to study the gasification reactions and mecha-nisms at laboratory scale and to produce clean gas but themain disadvantages of this type of gasifier are its low ther-mal efficiency and the great difficulties related to handlingbiomass with high moisture and ash contents [22]

34 Pyrolysis and Gasification Products Characterization

341 Syngas Composition

(1) Pyrolysis Syngas Composition The syngas chemical com-position obtained throughout SS pyrolysis is shown in Fig-ure 5(a) The major gaseous products obtained from SSpyrolysis are CH4 (up to 1762) CO2 (up to 1203)H2 (up to 1085) CO (up to 726) and C119899H119898 (up to430) From Figure 5(a) it could be roughly seen that thevariation of several produced gases is almost constant witha high release at the beginning of the experiment (from300∘C) to achieve maximum of combustible gas productionat 600∘C and finally a gradual decrease marking the end ofthe pyrolysis reactions Among combustible gases CH4 andH2 are found to be the most abundant compounds of the

produced gases from SS pyrolysis The H2 high content inthe syngas mixture produced by pyrolysis could be explainedby the catalytic effect of the minerals contained in studiedSS (ash content around 3080) This catalytic effect in SSpyrolysis was highlighted by many authors [12 16] whostudied the correlation between the H2 percentage producedby pyrolysis of SS and the SS ash content and demonstratedthat the catalytic effect of the ash in the dehydrogenationreactions enhances the H2 production whereas the highH2 production is often correlated directly to the high ashcontent of SS which have a catalytic effect during thermalcracking and mainly in the dehydrogenation reactions [1216] Moreover the formation of CO and CO2 could beattributed to the decomposition of oxygenated groups suchas decarboxylation and decarbonylation [32] Other worksthat were conducted on SS pyrolysis have reported similar gascompositions Reference [12] presented a syngas compositionproduced from SS pyrolysis with a high yield (between 45and 66) of CO and H2 and reported that the gas fromthe conventional oven is much richer in hydrocarbons (25)than that from themicrowave ovens (6ndash11) According to [1]that studied SS flash pyrolysis in a conical spouted bed reactorat 600∘C the gas mixture composition is as follows 35 ofCO2 23 of CO 23 of H2 and 24 of C1ndashC4 Reference[16] obtained with the pyrolysis of three SS samples a gasmixture containing up to 60 of CO2 34 of CO 28 ofH2 11 of CH4 and 2-3 of C119899H119898

The calorific value (LHV) of the produced gas mixtureobtained under the pyrolysis conditions used in the presentstudy reaches a maximum of 996MJkg indicating a highcontent of combustible gases in this gaseous mixture Thisrelatively elevated heating value of the gas mixture can bevalorized as an alternative source of heating for the pyrolysisreactor The obtained heating values of gases are in the samerange as those reported by previous studies In fact the

10 BioMed Research International

heating values of gases from conventional pyrolysis were130ndash140MJm3 whereas with the microwave method theheating values ranged from 66 to 86MJm3 [11] Reference[33] that studied the pyrolysis of SS reported that the releasedgases have a maximum heating value around 25MJm3

(2) Gasification Syngas Composition The syngas chemicalcomposition analysis throughout the gasification experiment(Figure 5(b)) reveals that the obtained syngas is a mixtureof the following main components CO2 (up to 1843) CO(up to 76) H2 (up to 732) CH4 (up to 536) andC119899H119898 (up to 236) As can be observed in Figure 5(b)when the reactor temperature increased the CO and CO2concentrations increased due to decarbonylation and decar-boxylation reactions at high temperatures H2 concentrationincreased also with the temperature increase with a max-imum around 732wt at nearly 900∘C and this is due tonot only the cracking reactions but also dehydrogenationreactions promoted by the catalytic effect of the inorganicfraction [1 16] CH4 and C119899H119898 showed the same trendwith a slight variation from the beginning These drawndata are in agreement with those described by [2] where atypical gasification gaseousmixture is characterized by a highhydrogen content (H2 889ndash1117 vol) It contains also othercombustible compounds including CO (628ndash1077 vol)CH4 (126ndash209 vol) carbon dioxide and some light hydro-carbons Similar observations have been advanced by [17] thatstudied SS gasification using downdraft reactor and indicatedthat produced syngas is composed mainly of combustiblegases such as H2 (880ndash1115 vol) CO (631ndash1063 vol)CH4 (125ndash207 vol) and C119899H119898 (076ndash110 vol) and non-combustible gases such as N2 and CO2

The heating value of the syngas obtained under thegasification conditions used in the present study reachesa maximum of 802MJkg This calorific value is higherthan those reported for SS pyrolysis Reference [18] reportedgross heating values ranging from 487 to 555MJkg forsyngas produced from SS gasification in a downdraft gasifierwhereas [34] advanced LHV values ranging between 415 and709MJkg for syngas produced from two types of SS

342 Bio-Oil and Biochar Properties The bio-oil elementalcomposition is as follows C 5659wt H 824wt N396wt S 032 wt and O 3089wt The obtained car-bon hydrogen and sulphur contents are lower than thosefound by other authors from pyrolysis of SS Thus [34]obtained for bio-oils produced from conventional pyrolysisof SS carbon content between 709 and 845 wt hydrogencontent between 103 and 124 wt and sulphur contentbetween 02 and 06 wt Reference [33] reported for organicfraction of SS pyrolysis liquids between 494 and 626wtfor carbon and between 98 wt and 115 wt for hydrogennitrogen and sulphur contents are almost invariable [33 35]The knowledge of elemental composition (mainly carbonhydrogen and sulphur contents) is necessary for potentialutilization of these bio-oils as biofuels or for further process-ing to petrochemicals or biodiesel

The bio-oil density at 15∘C kinematic viscosity and watercontents of both organic and aqueous fractions from SS

Table 3 Fuel properties of liquid fractions obtained from SSpyrolysis (at 550∘C and 15∘Cmin)

Density (15∘C)(KgL)

Viscosity(40∘C)(mm2s)

Water content()

Organic fraction 09743 63 16Aqueousfraction 1 106 25

pyrolysis are reported in Table 3The organic fraction densityaround 09743Kgm3 is quite higher than those required bythe Tunisian standard fuels (between 820 and 860 kgm3)and also higher than those of similar bio-oils obtained fromdifferent feedstocks [27] The organic fraction viscosity isaround 63 cSt while the aqueous fraction one is about106 cSt these values are considerably higher than those of theTunisian standard fuels (45 cSt) and those of other bio-oilsreported in [27] The water content of the organic fraction isquite high (around 16) and this may be reduced with payingattention to the decantation of the two liquid phases

The FTIR spectrum of bio-oil sample obtained from SSpyrolysis is given in Figure 6(a)The liquid bio-oil seems to bevery complex mixture with a high content of aliphatic groupsindicated by the presence of intense peaks in the absorptionregion between 2800 and 3000 cmminus1 and several peaksbetween 1300 and 1500 cmminus1 imputable to aliphatic CndashHdeformation The aromatic character of the bio-oil sample ismarked by the peak around 1640 cmminus1 corresponding to C=Cin aromatic structures and by many little peaks in the regionbetween 700 and 900 cmminus1

The biochar sample spectrum (Figure 6(b)) shows highcontent of O-containing functions the band centred around3300 cmminus1 due to the presence of OndashH groups and the highintensive band between 1000 and 1100 cmminus1 correspondingto CndashO stretching of carbohydrate and alcohol functionsThe aliphatic groupsrsquo content is indicated mainly by the largebandbetween 1300 and 1500 cmminus1 imputable to aliphaticCndashHdeformation Usually the produced biochar obtained from SSpyrolysis could be used as biofuel (high calorific value) oras chemical adsorbent of pollutants (substitute for activatedcarbon) or as soil fertilizer [35] The potential use of biocharsin these three options depends on their characteristics

343 Gasification Coproducts Characterization Figures 6(c)and 6(d) show the FTIR spectra obtained from condensabletars and solid residue produced from gasification of predriedSS respectively The FTIR condensable tar spectrum showsthe high complexity of these productsThe studied tar sampleis composed of aliphatic compounds and aromatic and O-containing groups with a large variety of organic compoundsThe solid residue spectrum exhibits a slight absorption bandbetween 3200 and 3600 cmminus1 attributable to CndashO stretchingbut a very intensive peak around 1400 cmminus1 corresponding toaliphatic groups We note the presence of many little peaksin the absorption region of 700ndash900 cmminus1 imputable to thearomatic stretching vibrations

BioMed Research International 11

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

0616055050045040035030025020015010005000

minus005minus010minus015minus020

minus0239

C=CndashCHaromCndashO

A

ndashOHndashNH

ndashCH

ndashCH

ndashCH

(cＧminus1)

(a)

minus0123minus005

000005010015020025030035040045050055060065070075080085

0908

C=C CHarom

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

CndashO

A

ndashOHndashNH

ndashCH

(cＧminus1)

(b)

minus00800010203040506070809101112

127

C=C40

0

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHaromCndashO

A

ndashOHndashNH ndashCH

ndashCH

(cＧminus1)

(c)

minus0100001020304050607080910111213

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHarom

ndashOHndashNH

ndashCH

ndashCH

(d)

Figure 6 FTIR spectra of (a) bio-oil sample obtained by SS pyrolysis (b) biochar sample obtained by SS pyrolysis (c) tar sample obtainedby SS gasification and (d) solid residue sample obtained by SS gasification

35 Mathematical Modeling Stoichiometric Model

351 Pyrolysis Balance Equation (8) of pyrolysis is

C120572H120573O120574 + 119909H2Oyields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VO2(8)

120572 120573 and 120574 are determined by the elemental analysis119905 119906 119910 and 119911 are the number of moles of gas species

calculated in Section 353119899C 119899O and 119899H are calculated in Section 351119909 ldquothe number of moles of H2Ordquo is the difference

between the number of moles of oxygen in the products andthat contained in biomass 120574 and it is calculated as follows

119909 = 119910 + 2119911 + 2V + 119899O minus 120574 (in mol) (9)

119899 is the difference between the number of moles of carbonin the initial biomass and that contained in the obtainedproducts and it is calculated as follows

119899 = 120572 minus 119899C minus 119910 minus 119911 minus 119906 (in mol) (10)

119898 is the difference between the number of moles of hydrogenin the reactant and that in the products and is calculated asfollows

119898 = 120573 + 2119909 minus 2119905 minus 4119906 (in mol) (11)

352 Gasification Balance The reaction of gasification isdescribed as follows

C120572H120573O120574 + 119909 (O2 + 367N2)yields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(12)

120572 120573 120574 and 120575 are determined by the elemental analysis

12 BioMed Research International

Table 4 Raw material and syngas stoichiometric model calcula-tions

Element Number of moles

Raw material

Carbon 106Hydrogen 21556Oxygen 1673Nitrogen 322Sulfur 078

Syngas

Mg 41993 g119899N2

000119899O2

000119899CH4

462119899CO 109119899CO2

118119899H2

2286

119905 119906 119910 119911 119901 and 119902 are the number of moles of the gasspecies calculated in Section 353119909 ldquothe number of moles of airrdquo is the difference between

the number of moles of oxygen in the products and thatcontained in the biomass and is calculated as follows

2119909 = 2119902 + 119910 + 2119911 minus 119909 minus 120574 (in mol) (13)

The number of moles 119901 of nitrogen produced is calculated asfollows

119901 = 119909 lowast 376 (in mol) (14)

119899 is the difference between the number of moles of carboncontained in the initial biomass and that contained in theproducts and is calculated as follows

119899 = 120572 minus 119910 minus 119911 minus 119906 (in mol) (15)

119898 is the difference between the number of moles of dihydro-gen in the reactants and that contained in the products and iscalculated as follows

119898 = 120573 minus 2119905 minus 4119906 (in mol) (16)

353 Calculations Table 4 shows the raw material andsyngas stoichiometric model calculations Pyrolysis and gasi-fication balances are respectively illustrated by (17) and (19)

For Pyrolysis

C120572H120573O120574 + 119909H2O 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VHO2(17)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 and 119911 are the number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses data

According to data reported in Table 4 we obtain theglobal SS pyrolysis formula

C106H21556O1673 + 1326H2O 997888rarr

109CO + 118CO2 + 2286H2 + 462CH4

+ C29909H1247 + VHO2

(18)

For Gasification

C120572H120573O120574 + 119909 (O2 + 367N2) 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(19)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 119911 119901 and 119902 are number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses dataAccording to data reported in Table 4 we obtain the

global SS gasification formula

C106H21556O1673 + 127 (O2 + 367N2) 997888rarr

32CO + 68CO2 + 5977H2 + 23CH4

+ C12762H8648 + 467N2 + 047O2

(20)

The obtained pyrolysis and gasification formulas describeaverage degradation of SS compounds under pyrolysis andgasification circumstances The model calculations allow usto study the influence of process parameters and thus topredict the desired products yields

4 Conclusions

In this study pyrolysis and gasification of Tunisian solar driedSS were performed separately using two different laboratory-scale reactors to produce mainly hydrogen-rich syntheticgas Through this work we highlighted the opportunity ofemployment of these two processes in the conversion ofTunisian SS into combustible gases and thus the potential ofsolar dried SS wastes as feedstocks for syngas productionThe released gases from pyrolysis (yield reaching 23wt)and gasification (yield reaching 82wt) present high calorificvalues (around 996MJm3 for pyrolysis and 802MJkg forgasification) due to their high contents of H2 (up to 1085and 732 resp) and CH4 (up to 1762 and 536 resp)The produced syngas should be used either as a fuel or as anintermediate in the production of liquid fuels and chemicalsWe suggest its reuse to supply a part of the energy needed inthe heating part of the reactor in order to enhance the energybalance of the process

Taking into account these experimental and numericalresults it can be concluded that the SS energy recovery viapyrolysis and gasification is a viable method for reducing thevolume of these harmful products with producing valuableproducts and alternative fuels in order to reduce the con-sumption of fossil fuels

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

10 BioMed Research International

heating values of gases from conventional pyrolysis were130ndash140MJm3 whereas with the microwave method theheating values ranged from 66 to 86MJm3 [11] Reference[33] that studied the pyrolysis of SS reported that the releasedgases have a maximum heating value around 25MJm3

(2) Gasification Syngas Composition The syngas chemicalcomposition analysis throughout the gasification experiment(Figure 5(b)) reveals that the obtained syngas is a mixtureof the following main components CO2 (up to 1843) CO(up to 76) H2 (up to 732) CH4 (up to 536) andC119899H119898 (up to 236) As can be observed in Figure 5(b)when the reactor temperature increased the CO and CO2concentrations increased due to decarbonylation and decar-boxylation reactions at high temperatures H2 concentrationincreased also with the temperature increase with a max-imum around 732wt at nearly 900∘C and this is due tonot only the cracking reactions but also dehydrogenationreactions promoted by the catalytic effect of the inorganicfraction [1 16] CH4 and C119899H119898 showed the same trendwith a slight variation from the beginning These drawndata are in agreement with those described by [2] where atypical gasification gaseousmixture is characterized by a highhydrogen content (H2 889ndash1117 vol) It contains also othercombustible compounds including CO (628ndash1077 vol)CH4 (126ndash209 vol) carbon dioxide and some light hydro-carbons Similar observations have been advanced by [17] thatstudied SS gasification using downdraft reactor and indicatedthat produced syngas is composed mainly of combustiblegases such as H2 (880ndash1115 vol) CO (631ndash1063 vol)CH4 (125ndash207 vol) and C119899H119898 (076ndash110 vol) and non-combustible gases such as N2 and CO2

The heating value of the syngas obtained under thegasification conditions used in the present study reachesa maximum of 802MJkg This calorific value is higherthan those reported for SS pyrolysis Reference [18] reportedgross heating values ranging from 487 to 555MJkg forsyngas produced from SS gasification in a downdraft gasifierwhereas [34] advanced LHV values ranging between 415 and709MJkg for syngas produced from two types of SS

342 Bio-Oil and Biochar Properties The bio-oil elementalcomposition is as follows C 5659wt H 824wt N396wt S 032 wt and O 3089wt The obtained car-bon hydrogen and sulphur contents are lower than thosefound by other authors from pyrolysis of SS Thus [34]obtained for bio-oils produced from conventional pyrolysisof SS carbon content between 709 and 845 wt hydrogencontent between 103 and 124 wt and sulphur contentbetween 02 and 06 wt Reference [33] reported for organicfraction of SS pyrolysis liquids between 494 and 626wtfor carbon and between 98 wt and 115 wt for hydrogennitrogen and sulphur contents are almost invariable [33 35]The knowledge of elemental composition (mainly carbonhydrogen and sulphur contents) is necessary for potentialutilization of these bio-oils as biofuels or for further process-ing to petrochemicals or biodiesel

The bio-oil density at 15∘C kinematic viscosity and watercontents of both organic and aqueous fractions from SS

Table 3 Fuel properties of liquid fractions obtained from SSpyrolysis (at 550∘C and 15∘Cmin)

Density (15∘C)(KgL)

Viscosity(40∘C)(mm2s)

Water content()

Organic fraction 09743 63 16Aqueousfraction 1 106 25

pyrolysis are reported in Table 3The organic fraction densityaround 09743Kgm3 is quite higher than those required bythe Tunisian standard fuels (between 820 and 860 kgm3)and also higher than those of similar bio-oils obtained fromdifferent feedstocks [27] The organic fraction viscosity isaround 63 cSt while the aqueous fraction one is about106 cSt these values are considerably higher than those of theTunisian standard fuels (45 cSt) and those of other bio-oilsreported in [27] The water content of the organic fraction isquite high (around 16) and this may be reduced with payingattention to the decantation of the two liquid phases

The FTIR spectrum of bio-oil sample obtained from SSpyrolysis is given in Figure 6(a)The liquid bio-oil seems to bevery complex mixture with a high content of aliphatic groupsindicated by the presence of intense peaks in the absorptionregion between 2800 and 3000 cmminus1 and several peaksbetween 1300 and 1500 cmminus1 imputable to aliphatic CndashHdeformation The aromatic character of the bio-oil sample ismarked by the peak around 1640 cmminus1 corresponding to C=Cin aromatic structures and by many little peaks in the regionbetween 700 and 900 cmminus1

The biochar sample spectrum (Figure 6(b)) shows highcontent of O-containing functions the band centred around3300 cmminus1 due to the presence of OndashH groups and the highintensive band between 1000 and 1100 cmminus1 correspondingto CndashO stretching of carbohydrate and alcohol functionsThe aliphatic groupsrsquo content is indicated mainly by the largebandbetween 1300 and 1500 cmminus1 imputable to aliphaticCndashHdeformation Usually the produced biochar obtained from SSpyrolysis could be used as biofuel (high calorific value) oras chemical adsorbent of pollutants (substitute for activatedcarbon) or as soil fertilizer [35] The potential use of biocharsin these three options depends on their characteristics

343 Gasification Coproducts Characterization Figures 6(c)and 6(d) show the FTIR spectra obtained from condensabletars and solid residue produced from gasification of predriedSS respectively The FTIR condensable tar spectrum showsthe high complexity of these productsThe studied tar sampleis composed of aliphatic compounds and aromatic and O-containing groups with a large variety of organic compoundsThe solid residue spectrum exhibits a slight absorption bandbetween 3200 and 3600 cmminus1 attributable to CndashO stretchingbut a very intensive peak around 1400 cmminus1 corresponding toaliphatic groups We note the presence of many little peaksin the absorption region of 700ndash900 cmminus1 imputable to thearomatic stretching vibrations

BioMed Research International 11

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

0616055050045040035030025020015010005000

minus005minus010minus015minus020

minus0239

C=CndashCHaromCndashO

A

ndashOHndashNH

ndashCH

ndashCH

ndashCH

(cＧminus1)

(a)

minus0123minus005

000005010015020025030035040045050055060065070075080085

0908

C=C CHarom

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

CndashO

A

ndashOHndashNH

ndashCH

(cＧminus1)

(b)

minus00800010203040506070809101112

127

C=C40

0

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHaromCndashO

A

ndashOHndashNH ndashCH

ndashCH

(cＧminus1)

(c)

minus0100001020304050607080910111213

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHarom

ndashOHndashNH

ndashCH

ndashCH

(d)

Figure 6 FTIR spectra of (a) bio-oil sample obtained by SS pyrolysis (b) biochar sample obtained by SS pyrolysis (c) tar sample obtainedby SS gasification and (d) solid residue sample obtained by SS gasification

35 Mathematical Modeling Stoichiometric Model

351 Pyrolysis Balance Equation (8) of pyrolysis is

C120572H120573O120574 + 119909H2Oyields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VO2(8)

120572 120573 and 120574 are determined by the elemental analysis119905 119906 119910 and 119911 are the number of moles of gas species

calculated in Section 353119899C 119899O and 119899H are calculated in Section 351119909 ldquothe number of moles of H2Ordquo is the difference

between the number of moles of oxygen in the products andthat contained in biomass 120574 and it is calculated as follows

119909 = 119910 + 2119911 + 2V + 119899O minus 120574 (in mol) (9)

119899 is the difference between the number of moles of carbonin the initial biomass and that contained in the obtainedproducts and it is calculated as follows

119899 = 120572 minus 119899C minus 119910 minus 119911 minus 119906 (in mol) (10)

119898 is the difference between the number of moles of hydrogenin the reactant and that in the products and is calculated asfollows

119898 = 120573 + 2119909 minus 2119905 minus 4119906 (in mol) (11)

352 Gasification Balance The reaction of gasification isdescribed as follows

C120572H120573O120574 + 119909 (O2 + 367N2)yields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(12)

120572 120573 120574 and 120575 are determined by the elemental analysis

12 BioMed Research International

Table 4 Raw material and syngas stoichiometric model calcula-tions

Element Number of moles

Raw material

Carbon 106Hydrogen 21556Oxygen 1673Nitrogen 322Sulfur 078

Syngas

Mg 41993 g119899N2

000119899O2

000119899CH4

462119899CO 109119899CO2

118119899H2

2286

119905 119906 119910 119911 119901 and 119902 are the number of moles of the gasspecies calculated in Section 353119909 ldquothe number of moles of airrdquo is the difference between

the number of moles of oxygen in the products and thatcontained in the biomass and is calculated as follows

2119909 = 2119902 + 119910 + 2119911 minus 119909 minus 120574 (in mol) (13)

The number of moles 119901 of nitrogen produced is calculated asfollows

119901 = 119909 lowast 376 (in mol) (14)

119899 is the difference between the number of moles of carboncontained in the initial biomass and that contained in theproducts and is calculated as follows

119899 = 120572 minus 119910 minus 119911 minus 119906 (in mol) (15)

119898 is the difference between the number of moles of dihydro-gen in the reactants and that contained in the products and iscalculated as follows

119898 = 120573 minus 2119905 minus 4119906 (in mol) (16)

353 Calculations Table 4 shows the raw material andsyngas stoichiometric model calculations Pyrolysis and gasi-fication balances are respectively illustrated by (17) and (19)

For Pyrolysis

C120572H120573O120574 + 119909H2O 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VHO2(17)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 and 119911 are the number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses data

According to data reported in Table 4 we obtain theglobal SS pyrolysis formula

C106H21556O1673 + 1326H2O 997888rarr

109CO + 118CO2 + 2286H2 + 462CH4

+ C29909H1247 + VHO2

(18)

For Gasification

C120572H120573O120574 + 119909 (O2 + 367N2) 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(19)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 119911 119901 and 119902 are number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses dataAccording to data reported in Table 4 we obtain the

global SS gasification formula

C106H21556O1673 + 127 (O2 + 367N2) 997888rarr

32CO + 68CO2 + 5977H2 + 23CH4

+ C12762H8648 + 467N2 + 047O2

(20)

The obtained pyrolysis and gasification formulas describeaverage degradation of SS compounds under pyrolysis andgasification circumstances The model calculations allow usto study the influence of process parameters and thus topredict the desired products yields

4 Conclusions

In this study pyrolysis and gasification of Tunisian solar driedSS were performed separately using two different laboratory-scale reactors to produce mainly hydrogen-rich syntheticgas Through this work we highlighted the opportunity ofemployment of these two processes in the conversion ofTunisian SS into combustible gases and thus the potential ofsolar dried SS wastes as feedstocks for syngas productionThe released gases from pyrolysis (yield reaching 23wt)and gasification (yield reaching 82wt) present high calorificvalues (around 996MJm3 for pyrolysis and 802MJkg forgasification) due to their high contents of H2 (up to 1085and 732 resp) and CH4 (up to 1762 and 536 resp)The produced syngas should be used either as a fuel or as anintermediate in the production of liquid fuels and chemicalsWe suggest its reuse to supply a part of the energy needed inthe heating part of the reactor in order to enhance the energybalance of the process

Taking into account these experimental and numericalresults it can be concluded that the SS energy recovery viapyrolysis and gasification is a viable method for reducing thevolume of these harmful products with producing valuableproducts and alternative fuels in order to reduce the con-sumption of fossil fuels

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

BioMed Research International 11

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

0616055050045040035030025020015010005000

minus005minus010minus015minus020

minus0239

C=CndashCHaromCndashO

A

ndashOHndashNH

ndashCH

ndashCH

ndashCH

(cＧminus1)

(a)

minus0123minus005

000005010015020025030035040045050055060065070075080085

0908

C=C CHarom

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

CndashO

A

ndashOHndashNH

ndashCH

(cＧminus1)

(b)

minus00800010203040506070809101112

127

C=C40

0

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHaromCndashO

A

ndashOHndashNH ndashCH

ndashCH

(cＧminus1)

(c)

minus0100001020304050607080910111213

400

600

800

1000

1200

1400

1600

1800

2000

2400

2800

3200

3600

4000

ndashCHarom

ndashOHndashNH

ndashCH

ndashCH

(d)

Figure 6 FTIR spectra of (a) bio-oil sample obtained by SS pyrolysis (b) biochar sample obtained by SS pyrolysis (c) tar sample obtainedby SS gasification and (d) solid residue sample obtained by SS gasification

35 Mathematical Modeling Stoichiometric Model

351 Pyrolysis Balance Equation (8) of pyrolysis is

C120572H120573O120574 + 119909H2Oyields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VO2(8)

120572 120573 and 120574 are determined by the elemental analysis119905 119906 119910 and 119911 are the number of moles of gas species

calculated in Section 353119899C 119899O and 119899H are calculated in Section 351119909 ldquothe number of moles of H2Ordquo is the difference

between the number of moles of oxygen in the products andthat contained in biomass 120574 and it is calculated as follows

119909 = 119910 + 2119911 + 2V + 119899O minus 120574 (in mol) (9)

119899 is the difference between the number of moles of carbonin the initial biomass and that contained in the obtainedproducts and it is calculated as follows

119899 = 120572 minus 119899C minus 119910 minus 119911 minus 119906 (in mol) (10)

119898 is the difference between the number of moles of hydrogenin the reactant and that in the products and is calculated asfollows

119898 = 120573 + 2119909 minus 2119905 minus 4119906 (in mol) (11)

352 Gasification Balance The reaction of gasification isdescribed as follows

C120572H120573O120574 + 119909 (O2 + 367N2)yields997888997888997888997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(12)

120572 120573 120574 and 120575 are determined by the elemental analysis

12 BioMed Research International

Table 4 Raw material and syngas stoichiometric model calcula-tions

Element Number of moles

Raw material

Carbon 106Hydrogen 21556Oxygen 1673Nitrogen 322Sulfur 078

Syngas

Mg 41993 g119899N2

000119899O2

000119899CH4

462119899CO 109119899CO2

118119899H2

2286

119905 119906 119910 119911 119901 and 119902 are the number of moles of the gasspecies calculated in Section 353119909 ldquothe number of moles of airrdquo is the difference between

the number of moles of oxygen in the products and thatcontained in the biomass and is calculated as follows

2119909 = 2119902 + 119910 + 2119911 minus 119909 minus 120574 (in mol) (13)

The number of moles 119901 of nitrogen produced is calculated asfollows

119901 = 119909 lowast 376 (in mol) (14)

119899 is the difference between the number of moles of carboncontained in the initial biomass and that contained in theproducts and is calculated as follows

119899 = 120572 minus 119910 minus 119911 minus 119906 (in mol) (15)

119898 is the difference between the number of moles of dihydro-gen in the reactants and that contained in the products and iscalculated as follows

119898 = 120573 minus 2119905 minus 4119906 (in mol) (16)

353 Calculations Table 4 shows the raw material andsyngas stoichiometric model calculations Pyrolysis and gasi-fication balances are respectively illustrated by (17) and (19)

For Pyrolysis

C120572H120573O120574 + 119909H2O 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VHO2(17)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 and 119911 are the number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses data

According to data reported in Table 4 we obtain theglobal SS pyrolysis formula

C106H21556O1673 + 1326H2O 997888rarr

109CO + 118CO2 + 2286H2 + 462CH4

+ C29909H1247 + VHO2

(18)

For Gasification

C120572H120573O120574 + 119909 (O2 + 367N2) 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(19)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 119911 119901 and 119902 are number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses dataAccording to data reported in Table 4 we obtain the

global SS gasification formula

C106H21556O1673 + 127 (O2 + 367N2) 997888rarr

32CO + 68CO2 + 5977H2 + 23CH4

+ C12762H8648 + 467N2 + 047O2

(20)

The obtained pyrolysis and gasification formulas describeaverage degradation of SS compounds under pyrolysis andgasification circumstances The model calculations allow usto study the influence of process parameters and thus topredict the desired products yields

4 Conclusions

In this study pyrolysis and gasification of Tunisian solar driedSS were performed separately using two different laboratory-scale reactors to produce mainly hydrogen-rich syntheticgas Through this work we highlighted the opportunity ofemployment of these two processes in the conversion ofTunisian SS into combustible gases and thus the potential ofsolar dried SS wastes as feedstocks for syngas productionThe released gases from pyrolysis (yield reaching 23wt)and gasification (yield reaching 82wt) present high calorificvalues (around 996MJm3 for pyrolysis and 802MJkg forgasification) due to their high contents of H2 (up to 1085and 732 resp) and CH4 (up to 1762 and 536 resp)The produced syngas should be used either as a fuel or as anintermediate in the production of liquid fuels and chemicalsWe suggest its reuse to supply a part of the energy needed inthe heating part of the reactor in order to enhance the energybalance of the process

Taking into account these experimental and numericalresults it can be concluded that the SS energy recovery viapyrolysis and gasification is a viable method for reducing thevolume of these harmful products with producing valuableproducts and alternative fuels in order to reduce the con-sumption of fossil fuels

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

12 BioMed Research International

Table 4 Raw material and syngas stoichiometric model calcula-tions

Element Number of moles

Raw material

Carbon 106Hydrogen 21556Oxygen 1673Nitrogen 322Sulfur 078

Syngas

Mg 41993 g119899N2

000119899O2

000119899CH4

462119899CO 109119899CO2

118119899H2

2286

119905 119906 119910 119911 119901 and 119902 are the number of moles of the gasspecies calculated in Section 353119909 ldquothe number of moles of airrdquo is the difference between

the number of moles of oxygen in the products and thatcontained in the biomass and is calculated as follows

2119909 = 2119902 + 119910 + 2119911 minus 119909 minus 120574 (in mol) (13)

The number of moles 119901 of nitrogen produced is calculated asfollows

119901 = 119909 lowast 376 (in mol) (14)

119899 is the difference between the number of moles of carboncontained in the initial biomass and that contained in theproducts and is calculated as follows

119899 = 120572 minus 119910 minus 119911 minus 119906 (in mol) (15)

119898 is the difference between the number of moles of dihydro-gen in the reactants and that contained in the products and iscalculated as follows

119898 = 120573 minus 2119905 minus 4119906 (in mol) (16)

353 Calculations Table 4 shows the raw material andsyngas stoichiometric model calculations Pyrolysis and gasi-fication balances are respectively illustrated by (17) and (19)

For Pyrolysis

C120572H120573O120574 + 119909H2O 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + VHO2(17)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 and 119911 are the number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses data

According to data reported in Table 4 we obtain theglobal SS pyrolysis formula

C106H21556O1673 + 1326H2O 997888rarr

109CO + 118CO2 + 2286H2 + 462CH4

+ C29909H1247 + VHO2

(18)

For Gasification

C120572H120573O120574 + 119909 (O2 + 367N2) 997888rarr

119910CO + 119911CO2 + 119905H2 + 119906CH4 + C119899H119898 + 119901N2 + 119902O2(19)

120572 120573 and 120574were determined using SS elemental analyses data119905 119906 119910 119911 119901 and 119902 are number of moles of gas species

calculated using syngas composition analyses119899 and 119898 were determined using biochar bio-oil and

syngas elemental analyses dataAccording to data reported in Table 4 we obtain the

global SS gasification formula

C106H21556O1673 + 127 (O2 + 367N2) 997888rarr

32CO + 68CO2 + 5977H2 + 23CH4

+ C12762H8648 + 467N2 + 047O2

(20)

The obtained pyrolysis and gasification formulas describeaverage degradation of SS compounds under pyrolysis andgasification circumstances The model calculations allow usto study the influence of process parameters and thus topredict the desired products yields

4 Conclusions

In this study pyrolysis and gasification of Tunisian solar driedSS were performed separately using two different laboratory-scale reactors to produce mainly hydrogen-rich syntheticgas Through this work we highlighted the opportunity ofemployment of these two processes in the conversion ofTunisian SS into combustible gases and thus the potential ofsolar dried SS wastes as feedstocks for syngas productionThe released gases from pyrolysis (yield reaching 23wt)and gasification (yield reaching 82wt) present high calorificvalues (around 996MJm3 for pyrolysis and 802MJkg forgasification) due to their high contents of H2 (up to 1085and 732 resp) and CH4 (up to 1762 and 536 resp)The produced syngas should be used either as a fuel or as anintermediate in the production of liquid fuels and chemicalsWe suggest its reuse to supply a part of the energy needed inthe heating part of the reactor in order to enhance the energybalance of the process

Taking into account these experimental and numericalresults it can be concluded that the SS energy recovery viapyrolysis and gasification is a viable method for reducing thevolume of these harmful products with producing valuableproducts and alternative fuels in order to reduce the con-sumption of fossil fuels

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

BioMed Research International 13

In practice for SS management policy in Tunisia theenergetic conversion using thermochemical processes is notdeveloped From the obtained results the feasibility andthe effectiveness of the SS thermochemical conversion wereproven and thus these valorization technologies could beproposed to rationalize the disposal of SS and to offer aneconomical alternative since the use of these biosolids mayrepresent a valid energy source

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportprovided by ldquotheMinistry of Higher Education and ScientificResearchrdquo in Tunisia for ldquothe National Research Programrdquoand the National Office for Sanitation ldquoONASrdquo as the partnerorganization for providing sewage sludge samples

References

[1] J Alvarez M Amutio G Lopez I Barbarias J Bilbao andM Olazar ldquoSewage sludge valorization by flash pyrolysis in aconical spouted bed reactorrdquo Chemical Engineering Journal vol273 pp 173ndash183 2015

[2] D Fytili and A Zabaniotou ldquoUtilization of sewage sludge in EUapplication of old and new methodsmdasha reviewrdquo Renewable ampSustainable Energy Reviews vol 12 no 1 pp 116ndash140 2008

[3] W Rulkens ldquoSewage sludge as a biomass resource for the pro-duction of energy Overview and assessment of the variousoptionsrdquo Energy and Fuels vol 22 no 1 pp 9ndash15 2008

[4] S Luo B Xiao Z Hu S Liu Y Guan and L Cai ldquoInfluenceof particle size on pyrolysis and gasification performance ofmunicipal solid waste in a fixed bed reactorrdquo Bioresource Tech-nology vol 101 no 16 pp 6517ndash6520 2010

[5] A Lopez I de Marco B M Caballero M F Laresgoiti andA Adrados ldquoInfluence of time and temperature on pyrolysisof plastic wastes in a semi-batch reactorrdquo Chemical EngineeringJournal vol 173 no 1 pp 62ndash71 2011

[6] ADonatelli P Iovane andAMolino ldquoHigh energy syngas pro-duction by waste tyres steam gasification in a rotary kiln pilotplant Experimental and numerical investigationsrdquo Fuel vol89 no 10 pp 2721ndash2728 2010

[7] I Ahmed andAKGupta ldquoEvolution of syngas from cardboardgasificationrdquo Applied Energy vol 86 no 9 pp 1732ndash1740 2009

[8] M Dudynski K Kwiatkowski and K Bajer ldquoFrom feathers tosyngas - Technologies and devicesrdquoWaste Management vol 32no 4 pp 685ndash691 2012

[9] Z ChenM Hu X Zhu et al ldquoCharacteristics and kinetic studyon pyrolysis of five lignocellulosic biomass via thermogravimet-ric analysisrdquo Bioresource Technology vol 192 pp 441ndash450 2015

[10] A Ben Hassen-Trabelsi N Jaouachi S Naoui T Kraiem andK Zaafouri ldquoHydrogen-rich syngas production from pyrolysisand gasification of palmitic fibersrdquo in Proceedings of the 20156th International Renewable Energy Congress IREC 2015 tunMarch 2015

[11] J A Menendez A Domınguez M Inguanzo and J J PisldquoMicrowave pyrolysis of sewage sludge analysis of the gasfractionrdquo Journal of Analytical and Applied Pyrolysis vol 71 no2 pp 657ndash667 2004

[12] A Dominguez J A Menendez M Inguanzo and J J Pıs ldquoPro-duction of bio-fuels by high temperature pyrolysis of sewagesludge using conventional and microwave heatingrdquo BioresourceTechnology vol 97 no 10 pp 1185ndash1193 2006

[13] E Agrafioti G Bouras D Kalderis and E DiamadopoulosldquoBiochar production by sewage sludge pyrolysisrdquo Journal ofAnalytical and Applied Pyrolysis vol 101 pp 72ndash78 2013

[14] K M Smith G D Fowler S Pullket and N J D GrahamldquoSewage sludge-based adsorbents A review of their productionproperties and use in water treatment applicationsrdquo WaterResearch vol 43 no 10 pp 2569ndash2594 2009

[15] J Alvarez G Lopez M Amutio J Bilbao and M OlazarldquoPreparation of adsorbents from sewage sludge pyrolytic charby carbon dioxide activationrdquo Process Safety and EnvironmentalProtection vol 103 pp 76ndash86 2016

[16] I Fonts M Azuara G Gea and M B Murillo ldquoStudy of thepyrolysis liquids obtained fromdifferent sewage sludgerdquo Journalof Analytical and Applied Pyrolysis vol 85 no 1-2 pp 184ndash1912009

[17] M E Sanchez J A Menendez A Domınguez et al ldquoEffect ofpyrolysis temperature on the composition of the oils obtainedfrom sewage sludgerdquo Biomass and Bioenergy vol 33 no 6-7 pp933ndash940 2009

[18] M Dogru A Midilli and C R Howarth ldquoGasification ofsewage sludge using a throated downdraft gasifier and uncer-tainty analysisrdquo Fuel Processing Technology vol 75 no 1 pp 55ndash82 2002

[19] C M Kinoshita S Q Turn R P Overend and R L BainldquoPower generation potential of biomass gasification systemsrdquoJournal of Energy Engineering vol 123 no 3 pp 88ndash99 1997

[20] M J A Tijmensen A P C Faaij C NHamelinck andM RMVan Hardeveld ldquoExploration of the possibilities for productionof Fischer Tropsch liquids and power via biomass gasificationrdquoBiomass and Bioenergy vol 23 no 2 pp 129ndash152 2002

[21] M Balat M Balat E Kirtay and H Balat ldquoMain routes for thethermo-conversion of biomass into fuels and chemicals Part 2Gasification systemsrdquo Energy Conversion andManagement vol50 no 12 pp 3158ndash3168 2009

[22] T K Patra and P N Sheth ldquoBiomass gasification models fordowndraft gasifier a state-of-the-art reviewrdquo Renewable andSustainable Energy Reviews vol 50 pp 583ndash593 2015

[23] A Sharma V Pareek and D Zhang ldquoBiomass pyrolysismdashareview of modelling process parameters and catalytic studiesrdquoRenewable and Sustainable Energy Reviews vol 50 pp 1081ndash1096 2015

[24] ASTM American Society for Testing and Materials ASTMInternational Philadelphia ASTM vol 74 D3176 1997

[25] S A Channiwala and P P Parikh ldquoA unified correlation forestimating HHV of solid liquid and gaseous fuelsrdquo Fuel vol81 no 8 pp 1051ndash1063 2002

[26] AFNOR French Association for Standardization Solid biofuels -AFNOR XP CENTS 14774-3 AFNOR XP CENTS 14775AFNOR XP CENTS 15148 2010

[27] A Ben Hassen-Trabelsi T Kraiem S Naoui and H Belay-ouni ldquoPyrolysis of waste animal fats in a fixed-bed reactorProduction and characterization of bio-oil and bio-charrdquoWasteManagement vol 34 no 1 pp 210ndash218 2014

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

14 BioMed Research International

[28] ldquoOrganization for Standardizationrdquo in Proceedings of the ISO3104 1994 ISO 12185 1996 ISO 3733 1999

[29] A C Redfield ldquoThe biological control of chemical factors in theenvironmentrdquo American scientist vol 46 pp 205ndash222 1958

[30] W-T Tsai J-H Chang K-J Hsien and Y-M Chang ldquoProduc-tion of pyrolytic liquids from industrial sewage sludges in aninduction-heating reactorrdquo Bioresource Technology vol 100 no1 pp 406ndash412 2009

[31] I Fonts G Gea M Azuara J Abrego and J Arauzo ldquoSewagesludge pyrolysis for liquid production a reviewrdquo Renewable andSustainable Energy Reviews vol 16 no 5 pp 2781ndash2805 2012

[32] H Fan H Zhou and J Wang ldquoPyrolysis of municipal sewagesludges in a slowly heating and gas sweeping fixed-bed reactorrdquoEnergy Conversion andManagement vol 88 pp 1151ndash1158 2014

[33] M Inguanzo A Domınguez J A Menendez C G Blanco andJ J Pis ldquoOn the pyrolysis of sewage sludge The influence ofpyrolysis conditions on solid liquid and gas fractionsrdquo Journalof Analytical and Applied Pyrolysis vol 63 no 1 pp 209ndash2222002

[34] SWherle ldquoGasification of a dried sewage sludge in a laboratoryscale fixed bed reactorrdquo Energy Procedia vol 66 pp 253ndash2562015

[35] T Karayildirim J Yanik M Yuksel and H Bockhorn ldquoChar-acterisation of products from pyrolysis of waste sludgesrdquo Fuelvol 85 no 10-11 pp 1498ndash1508 2006

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 201

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Molecular Biology International

GenomicsInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioinformaticsAdvances in

Marine BiologyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Signal TransductionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Evolutionary BiologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Genetics Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Enzyme Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Microbiology