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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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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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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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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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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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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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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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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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ET ZC362-L10