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Lecture 11
Dr.Vandana
Environmental Pollution Control ETZ C362 1
Wastewater Sampling and Analysis
Chapter 8
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Summary of Lecture 10
Environmental Pollution Control ETZ C362 2
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Potential uses of fresh water
Agriculture
Industrial
Household/ domestic
Power generation
Recreational
Reasons of Water stress
Population growth
Expansion of business activity
Rapid urbanization
Climate Change
Pollution
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Classification of waste water by their origin
1. Domestic waste waterWater discharged from residential and commercial
establishments. The pollutants in domestic waste water arise from
residential and commercial cleaning operations, laundry, food preparation,
body cleaning functions and body excretions.2. Industrial waste waterDischarged from manufacturing plants where water
is used for various processes and also for washing and rinsing of equipment,
rooms etc.
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Types of Water pollutants and their effects
Water pollutants can be classified into nine categories
1. Oxygen demanding waters
2. Disease causing agents3. Synthetic organic compounds
4. Plant nutrients
5. Inorganic chemicals and minerals
6. Sediments
7. Radioactive substances
8. Thermal discharges9. oil
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Process which affects which affects dissolved oxygen (DO) content in water
are reaeration, photosynthesis, respiration and oxidation of wastes.
Reaeration is the process by which O2transfer takes place from atmosphere to
water.
The rate of reaeration depends on the rate of absorption through the air-water
interface & on the rate of dispersion within the body of water beneath the
surface.
The transfer rate can be expressed as N= KL( CS- CL)
Cs- DO level of saturation
CL- actual concentration DO in waterKL- liquid phase mass transfer rate coefficient
N- mass flux of O2 across unit area of the surface in unit time
DO2deficit , CS- CL
Oxygen demanding waste
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Photosynthesis
In presence of solar radiation, green plants utilize CO2 and
inorganic nutrients present in the water to synthesize organic
materials & liberate O2.
DO level in day is comparatively higher than night.
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Effects of other pollutants
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Inorganic chemicals and Minerals
Inorganic acids
Inorganic salts
Metal and metal compounds
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Chapter 8: Waste Water Sampling and Analysis
Sampling can be two types : grab sample and composite sample
Grab samples: Shows only the prevailing conditions at the time of
sampling and are useful in determining the effects of extreme
conditions of the waste.
Composite sample can be obtained by collecting individual samples at
frequent intervals and mixing them together.
Sampling
Methods of Analysis -Determination of Organic matter
Dissolved Oxygen (DO)
Determined by Winklers method
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Biochemical Oxygen Demand (BOD) measure of the oxygen
utilized by microorganisms during the oxidation of organic
materials)
Chemical Oxygen Demand (COD)
Total Organic Carbon (TOC)
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Determination of Inorganic Matters
Nitrogen
Phosphorus Trace elements
Alkalinity
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Nitrogen
Important nitrogen containing chemical species in waste water systems are
ammonia, organic nitrogen, nitrite and nitrate.
Ammonia (NH3) containing nitrogen & organic nitrogen combindly called
Kjeldahl Nitrogen and which contribute ~ 99% of the total nitrogen indomestic waste water.
All form of nitrogen can be measured analytically by colorimetric
techniques.
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Determination of Kjeldahl Nitrogen
The method comprise with digestion of nitrogensample with sulfuric acid and catalyst, whichdecomposes the organic substance by oxidation toliberate the reduced nitrogen as ammonium sulfate.
Chemical decomposition of the sample is completewhen the medium has become clear and colorless.
The solution is then distilled with sodium hydroxidewhich converts the ammonium salt to ammonia. Theamount of ammonia present (hence the amount of
nitrogen present in the sample) is determined byseveral methods like back titration using boric acid andsodium carbonate or using Nessler reagent (potassiummercuric iodide).
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MAJOR REACTIONS
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The standard technique used for the determination of ammonia
is the Nessler method.
The neutralized sample is distilled to separate the ammonia
from interfering substances.
The ammonia in the distillate is reacted withNesslersreagent
(K2HgI4) and produces a yellowish-brown colloidal dispersion.
The colour intensity is directly proportional to the amount of
NH3 present and can be estimated photometrically.
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Another method is the phenol hypochlorite method.
Ammonia is treated with phenol and hypochlorite in
the presence of a catalyst to produce the blue colored
indophenol solution. The intensity of colour is proportional to the
ammonia concentration.
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Determination of nitrogen present as nitrite is based on the
diazotization of sulphanilic acid with nitrite followed by its
combination with N-(1-napthyl)-ethylenediamine
dihydrochloride to form a purple azodye.
The intensity of the colour is directly proportional to the nitrite
concentration.
Nitrogen present as nitrate can be analyzed by reducing it to
nitrite or ammonia which is determined by Cd reduction
method.
In Cd reduction method ,the nitrates are quantitatively reduced
by Cd to nitrite.
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The nitrite formed is measured by the diazotization method.
This method gives the sum of the nitrite and nitrate nitrogen,
a separate analysis of the nitrite is required.
Nitrates can be reduced to nitrites with Zn under controlledconditions and the nitirtes determined colorimetrically.
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Phosphorus
P exists in waste water as orthophosphate,
polyphosphate and organic phosphate
Orthophosphate is determined by colorimetric method.The sample is treated with ammonium molybdate under
acid conditions to form molybdophosphoric acid which is
then reduced by V/SnCl2 when a colour complex is
formed. The intensity of the colour is proportional to the
phosphate concentration in the solution.
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Polyphosphates are first hydrolyzed to orthophosphate in
acidic medium and then analyzed.
The amount of polyphosphate is obtained by subtracting the
amount of orthophosphate originally present in the samplefrom the result.
Organic P is first oxidized to phosphate ion & then analyzed.
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Trace elements
Major trace elements are: Cr, Pd, Zn and Cd
Trace elements are determined by AAS & colorimetry.
Dithiozone is the colorimetric reagent used for the
determination of Cd, Pb and Zn.
Acid digestion is required to eliminate the interference fromcyanide,nitrite, sulphide, sulphite etc.
These metals give a red/pink coloured complex which can be
extracted in a suitable solvent. The colour intensity is determined by a colorimeter or
spectrophotometer.
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Cr determination involves oxidation of the metal to the hexavalent state and its
reaction with diphenylcarbazide in acidic medium and a red-violet product is
formed and its intensity can be measured photometrically.
Atomic Absorption Spectrometry
Quite rapid, highly selective and
automated for monitoring effluent
streams.
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Alkalinity Reason: Presence of bicarbonates, carbonates and hydroxides of metal ions
such as Ca, Mg, Na and K.
Measured by titrating the sample with a standard acid.
If the pH of the original sample is higher than 8.3, the titration is carriedout using phenolphthalein indicator until it becomes colourless and this end
point is known as phenolphthalein alkalinity or bicarbonate equivalencepoint.
Bicarbonates are present in the original sample along with hydroxides andcarbonates and in such cases the sample is titrated with methyl orange
indicator.
Determination of alkalinity is important in water softening, chemicaltreatment of waste water, corrosion control and in removal of ammonia byair stripping.
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Physical Characteristics
Suspended solids
important in the analysis of waste waters.
The suspended matter contained in domestic waste waters and inmany industrial wastes is largely organic and responsible for asignificant portion of the oxygen demand.
Major parameter used to evaluate the quality of domestic andindustrial wastes.
Total solids in waste waters refers to the matter that remains asresidue after evaporation and drying at 103 to 1050C.
It can be classified as filterable solids and suspended solids.
Filterable solidsAble to pass through a specified filter and consistof colloidal and dissolved solids.
Colloidal solids10-3to 10-6mm
Dissolved solids- 10-6mm (exist as molecules and ions in solution).
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Suspended solids They are retained on the filter and theirminimum diameter is about 1microm.
Of the suspended solids, the settelable solids are those which
settle in a cone-shaped container in a definite time period. Classification of suspended solids on the basis of their
volatility at 6000C- volatile suspended solids(VSS) (organic
matter that is oxidised at this temp.) and fixed suspended
solids or non-volatile suspended solids (NVSS) (inorganic
fraction that remains as ash).
The suspended solids concentration can be measured by
gravimetric methods.
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Colour and Odour
Colour may be organic or mineral origin
Organic sources include algae, tannis, humic compounds etc.
Inorganic sources are Fe and Mn compounds, chemicals anddyes from various industries etc.
Odours in water are caused by algae and decaying vegetation
and also some inorganic substances like mercaptans,amines
and sulphides.
The odour causing substances are present in very small
quantities and are often complex. So its difficult to isolate and
identify them.
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The standard test method is the threshold dilution method in
which the odour bearing sample is diluted with oduor free
water , until a dilution is obtained which has a barely
perceptible odour.
The result is expressed in terms of the threshold odournumber (TO) which is given by
TO = ml of sample + ml of odour-free water/ ml of sample.
TO is a function of temperature, the test temp. should be
reported in all cases.
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Colour is measured by comparison with known standards.
Suspended matter in water can interfere with the measurement of colour.
The sample is centrifuged to separate the solids and analysis is made on
the clear portion.
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Bacteriological Measurements
The most popular method is based on determining the
content of indicator organisms in it and the principal
indicator organisms used are the coliform group of bacteria.
The coliform bacteria has the ability to ferment lactose or
lauryl tryptose broth and produce gas. This we can use as asimple test to check the presence of coliform group.
Two general method used to obtain the number density of
coliform organisms in the test sample are membrane filter
technique and the most probable technique (MPT).
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Membrane filter technique: A known volume of the watersample is passed through the filter that has a very small pore
size. The coliform bacteria are captured by the filter and the
filter is exposed to nutrients which promote the growth of
coliform while inhibiting that of other organisms.
After incubation (2448hrs), the number of coliform colonies
is counted and their density is determined. The coliform
colonies appear pinkish in colour and their count is made with
the aid of an optical device.The coliform density is reported interms of total colifroms per 100ml.
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The most probable number (MPN) of organisms is a statistical estimate of
their density and is based on the examination of a number of portions of
different sizes giving +ve orve results for coliforms .
t u
N1, N2, N3sizes of portions examined
P,r,tno.of portions of respective sizes giving +ve results a- constant for any particular set of conditions
q,s,uno. of portions of respective sizes givingve results and therefore may be omitted for computing
conc. Of coliforms/ml
Y- probability of occurrence of a particular result
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Limitations
Coliform often grow in treatment facilities or water bodies and the tests can reveal
high populations even though pathogens are far less likely to multiply under the
same environmental conditions.
Some viruses and several organisms may survive for longer periods than coliforms,
and reduction of coliforms to low concentrations or even to zero may not always
indicate that the water is safe.
The MPN is that value of which gives a maximum value of Y.
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Here the MPN is
0.47 per ml at
which aY is
maximum or we
can say that the
MPN per 100ml
is 47.
U= 3
0.48
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Water quality standards
Water quality standards are to ensure the water quality in a
resource is suitable for the proposed use.
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Chapter 9 : Wastewater Treatment
Objectives:
Basic processes of water treatment
Advanced wastewater treatment
Recovery of materials from process effluents
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Treatment
Physical
Biological
Chemical
Screening, Sedimentation,
floatation and filtration
Precipitation, Coagulation anddisinfections
Biofiltration and Activated
Sludge Process
Physical &
Chemical
Air stripping, Carbon
adsorption, Oxidation and
reduction, Ion exchange, andmembrane Processes
Purpose of waste water treatment
Remove the contaminants from water so that the treated water can meet the
acceptable quality standards
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Another classification of waste water treatment processes
Primary Treatment
Removes identifiable suspended solids and floating matter
Secondary Treatment
Also known as biological treatment (organic matter that is soluble or in thecolloidal form is removed
Tertiary Treatment
Also known as advanced waste treatment (may involve physical, chemical orbiological processes)
Pretreatment
Primary Treatment Process
FlotationSedimentation
Discrete Settling Flocculent Settling Zone Settling
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Primary Treatment
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Pretreatment To remove large floating and suspended solids .Also include flow measurement
and prechlorination to prevent odours.
Consist of screening and grit removal.
Fixed bar screens are the most common types screens used in domestic waste
water treatment facilities.
Bar Screen
- catches large objects
such as bricks, bottles,pieces of wood, etc.
Pretreatment
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Is used to remove large floating and suspended solids. This process consists of
screening and then grit removal
Screening
Manuallyraked bar screen
Mechanically-raked bar screen
Apertures in the
range of 25-
50mm
Openings
ranging
from 5-40
mm
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The screening process produces objectionable screenings whichmust be disposed of in a satisfactory manner.
Methods of disposal include burial, incineration, grinding and
digestion.
To avoid the disposal problems, a device known as a comminutorcan be used instead of the screens.
The comminutor grinds large solids which can then be handled in
the sedimentation tank.
After screening, the waste water enters a grit chamber for the
removal of inorganic grit, consisting of sand, gravel, cinders and
pebbles.
Alternative of Screening
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Comminuter
Grit Chamber
After screening, the wastewater enters into a grit chamber for the removal of inorganicgrit, consisting of sand, gravel and pebbles. These chambers are generally designed
as long chambers and the velocities of waste flow is reduced to 3 cm/sec, whichallows settling of the grit material. The grit can be removed by scrappers.
Grit chambers are provided to protect pumps from abrasion and to reduce theformation of heavy deposits in pipes and channels.
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Grit chambers are provided to protect pumps from abrasion and
to reduce the formation of heavy deposits in pipes and channels.
Two types of grit chambers: horizontal flow and aerated.
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Wastewater Treatment
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Preliminary Treatment
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Sedimentation
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The settleable solids are removed by gravitational settling under
quiescent conditions.
The sludge formed at the bottom of the tank is removed either
by vacuum suction or by raking it to a discharge point at the
bottom of the tank for withdrawal. The clear liquid produced is known as the overflow and it should
contain no readily settleable matter.
The sedimentation may be carried out in rectangular horizontal
flow, circular radial flow or vertical flow basins.
SedimentationThe solids are removed by gravitational settling The sludge formed at the bottom of
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The solids are removed by gravitational settling. The sludge formed at the bottom ofthe tank is removed as underflow either by vacuum suction or by raking it to adischarge point
Equipments
Rectangular Horizontal flow
Sludge Scrapper It conveys the overflow from the chamber to the outlet section
It prevents the sludge to go out with the overflow
It helps to come out the sludge pushing the settle solids into a sludge hopper.
Circular radial flow
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Circular radial flow
Over flow is collected at weirs. A rotary
sludge scrapper (rotate as a fan) forces
the settle sludge down into a central
hopper
Vertical flow
It is used for small scale operation. A
sludge blanket (filter for small particles is
maintained in the lower part of the tank
through which the suspension rises.
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Flotation
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Used in place of sedimentation, for treating industrial waste
waters containing finely divided suspended solids and oily
matter.
This technique is used in paper industry to recover fine fibres
from the screened effluent and in the oil industry for theclarification of oil bearing waste.
Also used for treating effluents from tannery, metal finishing,
coldrolling, and pharmaceutical industries.
Particles of density close to that of water are very difficult tosettle in normal sedimentation tanks and take a long time for
separation.
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The separation can be speeded up by aerating the effluent
whereby the air bubbles are attached to the suspended
matter.
This has the effect of increasing the buoyancy of the particles,
as a result particles float to the surface.
To aid the flotation process , chemical coagulants such as
aluminium and ferric salts or polymer coagulant-aids are used.
Two types of flotation : Dispersed air flotation and dissolved
air flotation.
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In dispersed air flotation, air is introduced directly into the
liquid through a revolving impeller or through diffusers.
This technique is not a favored tech. in the treatment of
municipal waste waters.
In dissolved air flotation, air is brought into contact with the
waste water at a pressure of several atmosphere when air is
dissolved.
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baffleDissolved air flotation system without recycle
Dissolved air flotation system with recycle
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