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Chapter 7
Sources and Classification of Water Pollutants
Dr. Vandana
ETZ C362 Environmental pollution Control BITS Pilani
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Outlines
Sources of water pollutants
Types of water pollutants and their effects
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Two potential sources of water for human use
1. Desalinated sea water or brackish ground water
2. Reclaimed waste water
Utilization of water
Water resources are developed for irrigation, domestic use, power generation and
industrial use
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Classification of waste water by their origin
1. Domestic waste water Water 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.
Waste water may be classified as strong, medium or weak depending on the
amount of physical , chemical and biological constituents of wastewaters. The constituents of waste water varies from organic solvents, oils, suspended
solids to dissolved chemical compounds.
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Types of Water pollutants and their effects
Water pollutants can be classified into nine categories
1. Oxygen demanding wastes
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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The value of k1varies with the type of waste and the temperature.
The methods used to determine the k1and Lu
1. The least squares method
2. The method of moments
3. The daily difference method
4. The rapid rate method
5. The Thomas method
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Why BOD is so important?
Drinking water usually has a BOD of less than 1 mg/l
BOD of 3mg/lwater is fairly pure
BOD of 5mg/l
Purity is less
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During the carbonaceous stage, ammonia is produced by the breakdown of
organic nitrogen materials.
Ammonia (or ammonium ion) oxidized to nitrite and then to nitrate by
Nitrosomonas and Nitrobacter microorganism respctly.
2NH4++ 3O2 2NO2
-+ 2 H2O + 4H+
2 NO2-+O2 2 NO3
-
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The simultaneous action of deoxygenation and reaeration can
be described by the equation,
dD/dt = k1Lk2D
D- dissolved oxygen deficit
k1- deoxygenation constant
k2reaeration constant
L= Conc. Of the organic materialthe BOD remaining in time t
L = Lue-k1t
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D= oxygen deficit in time t
D0- initial oxygen deficit at the point
of waste discharge
K2,T = reaeration constant at temp. T0C
K2,20=reaeration const.at temp.200C
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BITS Pilani, K K Birla Goa Campus
Effects of other pollutants
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BITS Pilani, K K Birla Goa Campus
Pesticides can be classified in to insecticides, herbicides and fungicides.
Sources: Result from surface run off from agricultural lands, waste
discharge by pesticide Manufactures and by other means.
Detergents: Active ingredient
surfactant or surface active agent.Surfactant lowers the surface tension and allows dirt particles to
become linked to the water.
The acceptable concentration for surfactants in water is 0.5 ppm.
The presence of surfactants reduces the rate of oxygen absorption inwater.
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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control
Inorganic chemicals and Minerals
Inorganic acids
Inorganic salts
Metal and metal compounds
Inorganic Acids
Source:a) Mine drainage (mining of sulphur bearing ores containing lead, zinc, copper and iron
sulphide (pyrite)
b) Acidic rainfall
Effects:
a) Acids cause corrosion of metals and concrete
b) Acids are fatal to fish
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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control
Inorganic Salts
Source:Industrial effluents, salt from mines or from oil wells, and ocean salts.
Effects:
Salts causes hardness of water
Hard water can cause scale formation in pipes, boiler tubes and other industrial
equipments
Fatal to fish.
Metal
Cadmium
Source:waste streams from pigment works, textiles, electroplating, chemical plantsetc.
Permissible Level: 0.01 mg/l (drinking water)
Effects: It is not easily detectable in filtered water, particularly if the pH is neutral oralkaline.
Itai-Itai disease in Japan was probably due to cadmium
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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control
Chromium
Source: Waste water of plating operations, paint and dye operation, wastewater
from textile, ceramic and glass industry.
Permissible level: 0.05 mg/l (Drinking water)
Effects: Many plant species are adversely affected by chromiumLead
Source: Effluents from battery manufacture, printing, painting.
Permissible Level: 0.05 mg/L (Drinking water)
Effects: Is a cumulative poison and responsible for cancer.Mercury
Source: Effluents of Pesticides, Fertilizer Paint and paper, Chlorine industry
PermissibleLimit :0.002 mg/l (Drinking water)
Effects: Most toxic aquatic pollutant effects on photosynthesis rate.
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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control
Silver
Source: electroplating and photographic industries.
Permissible Limit : 0.05 mg/l (Drinking water)
Effects: Cumulative poison and chronic ingestion can cause a permanent discoloration ofskin in humans. Fish and lower organisms are susceptible to silver poisoning and silver
concentrations of 0.0004 to 0.4 mg/l have proved toxic.
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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control
Sediments
Sediments include soil, sand and mineral particles
Source:
a) By storms and flood waters
b) Deposits of sewage sludge, pulverized coal ash, industrial solids.
Effects:
a) Pumping equipments, power turbines are affected.
b) Reduces the amount of sunlight, food etc. for water plants, fish and other aquatic
bodies.
Radioactive substancesSource: Wastes of uranium refining, thorium mining, wastes from nuclear power
plants, and from industrial use of radioactive materials.
Effects: Radioactive substances can enter humans with food and water, and get
accumulated in blood, and thyroid gland, liver, bone and muscular tissues.
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Thermal Discharge
Source:
Power plant industry uses large qualities of water for cooling purposes and directly
discharge to water bodies. Consequently, the water temperature is increased,
and hot water layer at the top and cold water layer at the bottom are formed.The hot layer denied the oxygen transfer from atmosphere to cold water. Thus,
DO levels falls rapidly. And at high temperature the metabolic activity of micro-
organisms is increased. So, the increase of temperature results to decrease of
DO level and to increase of oxygen consumption.
Effects:a) Cold water fish may dies
b) An increase in temperature also increases the toxicity of some chemical
pollutants.
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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control
Oil
Source: Oil refineries, storage tanks, automobile waste oil, petrochemical plants,tank washing.
Effects:
a) Oil is insoluble in water, it floats and spreads rapidly into a thin layer. This layer
can prevent oxygen transfer from the atmosphere, diseases the DO level and
creates anaerobic conditions.
b) At sea, many birds are died by oil slicks.
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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control
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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control
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BITS Pilani, Pilani CampusET ZC362: Environmental Pollution Control
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BITS Pilani, K K Birla Goa Campus
Chapter 8
Waste Water Sampling and Analysis
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Outlines
Learning objectives
Sampling
Wastewater analysis
41
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Sampling
Two types of samples can be taken : grab sample and composite sample
Grab samples: Shows only the prevailing conditions at the time ofsampling 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.
f i i i f
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Methods of Analysis -Determination of
Organic matter
Dissolved Oxygen (DO)
Surface waters of good quality should be saturated with DO. Anyfall in DO level is one of the first indications that a water body is
polluted by organic matter.
It is usually determined by Winkler's method", which is based on thereaction of DO with manganese ions to form a precipitate ofmanganese dioxide.
Manganese dioxide is then treated with iodide ions when iodine isliberated in an amount chemically equivalent to the original DO.
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Dissolved Oxygen (DO)
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The interference can also be overcome by using DO analyzers
with membrane electrodes.
The plastic membrane has the selective ability of allowing
oxygen to diffuse through but preventing interfering ions.
The DO after diffusing through the membrane, reacts with the
metal electrode and causes a cell current which is proportional
to the oxygen concentration in the sample.
The calibration of the analyzer is done by measuring the DO of
a sample of known oxygen content ( determined by Winklermethod).
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Biochemical Oxygen Demand (BOD)
Most widely used & accepted measure of biodegradable organiccontent of wastewater is 5-day, 20OC BOD value. Brief analyticalprocedure is outlined below:
1. Two standard 300-ml BOD bottles are filled completely with
the wastewater of which the BOD is to be measured and thebottles are scaled.
2. Oxygen content of one bottle is determined immediately.
3. The other bottle is incubated at 20 oC for 5 days in total
darkness, after which its oxygen content is measured 4. The difference between the two DO values is the amount of
oxygen that is consumed by microorganisms during the 5 daysand is reported as the BOD5value of the sample.
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The wastewaters may have a high oxygen demand, high enough to
deplete all the dissolved oxygen in the sample before the end of 5 days,
thus making the test indeterminate.
The sample is diluted with high purity water to prevent total depletion
of DO. The diluting water is made up of deionized water to which
appropriate nutrients, phosphate buffer, trace elements, and seed
organisms (usually settled domestic sewage) are added.
A blank is run on the diluting water so that the oxygen demand of the
same material can be subtracted from the results. The BOD5is calculatedfrom the following equation:
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When the standard 5-day/20oC conditions are used, approximately
two-thirds of the carbonaceous material is broken down; an
incubation of about 20 days is needed for nearly complete
breakdown.
Nitrogenous nutrients can create problems in-the BOD test.
However, because of the slowness of the nitrification process, the
oxygen demand of the nitrifying bacteria is assumed to be negligible
in the standard 5-day incubation period at 20oC.
Actual environmental conditions of temp, biological population,
oxygen concentration, etc., are impossible to reproduce in the test;
hence, care must be taken to extrapolate the test results
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Many industrial wastewaters contain toxic materials which interfere with
the growth of microorganisms thus making the BOD test unreliable.
Similarly, the presence of algae in the wastewater affects the BOD test
by leading to higher BOD values even when the test is performed in
darkness.
BOD test is repalced by COD test!!!
Ch i l O D d (COD)
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Chemical Oxygen Demand (COD)
In the COD test, the oxidizing bacteria of the BOD testare replaced by a strong oxidizing agent under acidicconditions.
A sample of the wastewater containing organic material
is mixed with an excess of potassium dichromate &sulphuric acid & the mixture is heated under totalreflux conditions for a period of 2 hrs.
During digestion, the chemically oxidizable organic
material reduces a stoichiometrically equivalent amountof dichromate, the remaining dichromate is titrated withstandard ferrous ammonium sulphate
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The amount of potassium dichromate reduced gives ameasure of the amount of oxidizable organic material.Dichromate has advantages over other oxidants inoxidizing power and applicability to a wide variety of
samples. The COD test does not distinguish between organic
materials that are biodegradable and those that are
not, and, hence, gives a measure of the total oxidizable
organic material in the sample. Due to this, the COD test results are higher than those
of BOD tests carried out on the same sample.
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If inorganic substances such as chlorides and nitritesare present in the waste water, they interfere with theCOD test since they are also oxidized by dichromate
Chloride interference can be eliminated by adding
mercuric sulphate to the sample prior to the addition ofother reagents, and nitrite interference can be overcome
by adding sulphamic acid to the di-chromate solution
The COD test is much more useful than the BOD test
for estimating the oxygen requirements of certainindustrial wastewaters.
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It is valuable for wastes where BOD test is notapplicable due to the presence of toxic substances,low rate of oxidation, or other similar factors.
Ratios of BOD to COD can be employed to get anindication of the degree of biotreatability of thewaste.
Ratios of 0.8 or higher indicate wastes that are-
highly amenable to biological treatment, whilelower ratios indicate that the wastes are notfavorable to biological treatment.
T t l O i C b (TOC)
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Total Organic Carbon (TOC)
Total organic carbon test is based - on theoxidation of the carbon of the organic matter toCO2, which is measured by non-dispersiveinfrared analyzer.
Alternatively, the CO2 can be reduced tomethane, which is then measured by a FID (FlameIonisation Detector)
In this test, a few micro-litres (5 to 10 ) of the
aqueous sample are injected into a combustiontube containing a catalyst & heated to 900oC in aconstant flow of air.
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Water is vaporized and the carbonaceous matter isoxidized to CO2. and steam. Outside the combustiontube, the steam is condensed and removed.
CO2 is swept into a non-dispersive infrared analyzer,
which measures the amount of CO2. The concentration of CO2is directly proportional to the
concentration of total carbon present in the originalsample and it includes both organic and inorganiccarbon.
Inorganic carbon can be measured separately using anacid catalyst at 150oC, which is below the temperatureat which organic matter is oxidized.
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Schematic diagram of total organic carbon analyser
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Organic carbon content can then be obtained bysubtracting the inorganic carbon from the total result.
The TOC test can be performed in a relatively short
period of time (few minutes) compared to BOD andCOD measurements and, hence offers a valuablesupplement to BOD and COD estimations. Because ofthis advantage, an empirical correlation between TOCand COD or BOD, that is specific to a particular plant
operation, can be established and from this it is possibleto obtain a tentative estimate of the plant performancequickly.
D t i ti f I i M tt
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Determination of Inorganic Matters
Nitrogen
Phosphorus
Trace elements
Alkalinity
NITROGEN
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NITROGEN
Major nitrogen species are ammonia, organic
nitrogen, nitrites and nitrates.
Ammonia (NH3) containing nitrogen & organic
nitrogen combindly called Kjeldahl Nitrogen
and which contribute ~ 99% of the total
nitrogen in domestic waste water.
All form of nitrogen can be measuredanalytically by colorimetric techniques.
Determination of Kjeldahl Nitrogen
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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).
MAJOR REACTIONS
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MAJOR REACTIONS
Phosphorus
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Phosphorus
P exists in waste water as orthophosphate,polyphosphate and organic phosphate
Orthophosphate is determined by colorimetricmethod. The sample is treated with ammonium
molybdate under acid condition to formmolybdophosphoric acid which is then reducedby V/SnCl2to make color sample.
Polyphosphate are first hydrolyzed to
orthophosphate and then analyzed. Organic P is first oxidized to phosphate ion & then
analyzed
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Trace elements and Alkalinity
Major trace elements are: Cr, Pd, Zn Cd
Trace elements are determined by AAS & colorimetry.
Alkalinity in waste water is due to presence of carbonates, bicarbonates,
metal hydroxides.
Alkalinity is measured by titrating the sample with N/50 H2SO4
Determination of alkalinity is important in water softening, chemical
treatment of waste water, corrosion control, and in removal of ammoniaby air stripping.
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