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408-Environmental pollution and Industrial waste management

Wastewater treatment

ORIGIN OF WASEWAER

Wastewaters can be classified by their origin as domestic wastewater and industrial

wastewater. Any combination of wastewaters that is collected in municipal sewers istermed as municipal sewage. Domestic wastewater is that which is discharged fromresidential and commercial establishments, whereas industrial wastewater is that which isdischarged from manufacturing plants. The pollutants in domestic wastewater arise fromresidential and commercial cleaning operations, laundry, food preparation, body cleaningfunctions, and body excretions. The composition of domestic wastewater is relativelyconstant.Industrial wastewater is formed at industrial plants where water is used for variousprocesses, and also for washing and rinsing of equipment, rooms, etc. These operationsresult in the pollution of the nearby aquatic systems because some of the products andbyproducts are discharged, either deliberately or unintentionally into them.

ormally, wastewaters are conducted to treatment plants for removing undesirablecomponents which include both organic and inorganic matter as well as soluble andinsoluble material. These pollutants, if discharged directly or with improper treatment,can interfere with the self!cleaning mechanisms of water bodies. The capacity for self!cleaning is due to the presence of relatively small numbers of different types of micro!organisms in the water bodies. These micro!organisms use as food much of the organicpollutants and brea" them down into simple compounds such as #$%or methane, and themicro!organisms produce new cells also. &ut often either a pollutant does not degradenaturally or the sheer volume of the pollutant discharged is sufficient to overwhelm theself!cleaning process. Also, the microbial population can be destroyed by toxic wastesdischarged into the waterway. If that happens, the pollutant concentrations will build up

and reach high enough levels that will prevent re!establishment of a microbial population.The water quality thus becomes permanently degraded.'arious constituents of wastewater are potentially harmful to the environment and tohuman health. In the environment, the pollutants may cause destruction of animal andplant life, and aesthetic nuisance. Drin"ing water sources are often threatened byincreasing concentration of pathogenic organisms as well as by many of the new toxicchemicals disposed of by industry and agriculture. Thus, the treatment of these wastes isof paramount importance.

Wastewater !omposition

Depending on the amounts of physical, chemical, and biological constituents ofwastewaters, they may be classified as strong, medium, or wea".

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a"le #$ %pi&al &omposition o' domesti& wastewater

#onstituent #oncentration(trong )edium Wea"

(olids, total *%++ ++ -+Dissolved solid, total /+ ++ %+

fixed % -++ *0volatile -% %++ *+

(uspended solids, total -+ %++ *++fixed + -+volatile % *+ +

(ettleable solids 1ml2*3 %+ *+ &iochemical oxygen demand, !days, %+4# -++ %++ *++Total organic carbon 1T$#3 %++ *- 5#hemical oxygen demand 1#$D3 *+++ ++ %+itrogen 1total as 3 / 0+ %+ $rganic - * /

6ree ammonia + % *% itrites + + + itrates + + +7hosphorus 1total as 73 %+ *+ 5 $rganic - % Inorganic * 0#hlorides *++ + -+Al"alinity 1as #a#$-3tt %++ *++ +8rease *+ *++ +tAll values except for settleable solids are expressed in mg2l.tt'alues should be increased by amount in carriage water.

Typical compositions for domestic wastewater are given in Table *. The compositionsand concentrations are highly variable, and hence, the table is intended only to serve as aguide and not as a basis for design. Data on typical characteristics of municipal sewage insome urban cities of India are given in Table %.

a"le ($ !omposition o' sewage in some ur"an &ities o' India

#onstituent Delhi 9anpur )adras :yderabad Ahmedabad(uspended solids 1mg2l3 -0 5+ + ;/ *0/

TD( 1mg2*3 /+- *+++ **+ %- *5++ &$D, at %+4# 1mg2*3 %+- % -% --; *-- #$D 1mg2*3 - -% < < #$D = chemicaloxygen demand

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The composition of industrial wastewater is quite varied, its constituents ranging fromorganic solvents, oils, suspended solids to dissolved chemical compounds. Table - lists anumber of potentially polluting chemical substances released by different industries.)ost of the chemicals are toxic and some are even suspected of causing cancer. (uch?cancer suspect agents? include 0!nitrobiphenyl, 0!aminodiphenyl, @! and !naph!

thylamine, methyl chloromethyl ether, benBidine, -, -C!dichlorobenBidine, !propiolactone, 0!dimethylaminoaBo!benBene, !nitrosodimethylamine and vinyl chloride.Another important aspect of industrial wastewaters is that some of the chemicals arevaluable enough to warrant recovery. This aspect of recovery has ta"en on a newperspective in recent years and the recovered substance can either be recycled within theplant, or offered to other companies for use as basic or intermediate chemicals.

a"le )$ *a+or pollutants in various industries7ollutants Industry typet

$rganic

7roteins 1*3, 1%3, 1-3, 103, 1*-3 #arbohydrates 1*3, 1%3, 1-3, 13, 153, 1*-3 6ats and oils 1*3, 1%3, 1-3, 103, 13, 1;3, 1*+3, 1**3, 1*%3, 1*-3 Dyestuffs 1-3, 103, 13, 153 $rganic acids 153, 1*-3 7henols 1-3, 153, 13, 1/3, 1;3, 1*+3, 1**3 Detergents 1*3, 1-3, 1*%3, 1*-3 $rgano!pesticides 1%3, 1*-3Inorganic Acids 1-3, 153, 1*+3, 1**3 Al"alies 1-3, 153, 13, 1/3, 1*+3, 1**3, 1*%3

)etals 1-3, 13, 153, 1*+3, 1**3, 1*-3 )etallic salts 103, 13, 1*+3, 1**3, 1*-3 $ther salts 1*3, 1-3, 103, 13, 153 7hosphates, nitrates 1*3, 1-3, 103, 13, 153 &leaches 1-3, 13, 1*%3 (ulphides 1-3, 103, 13, 1/3 #yanides, cyanates 1/3, 1*+3, 1**3 #hromates 103, 13, 1*+3, 1**3 )inerals 1china clay and soil3 1*3, 13, 1*-3

tIndustry type 1*3 dairy, 1%3 food processing, 1-3 textiles, 103 tanning, 13 paper ma"ing,

153 chemical, 13 petro!chemical, 1/3 co"e ovens, 1;3 industrial oilproduction, 1*+3 engineering, 1**3 metallurgy, 1*%3 laundry and 1*-3agriculture.

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!,ara&teriation o' wastewaters 1Dara *, p.+3Waste waters are characteriBed on the basis of various physical, chemical and biologicalcharacteristics apart from flow data details1*3 .,%si&al !,ara&teristi&s$ #olour, odour, dissolved oxygen 1D.$.3, insolublesubstances 1settleable solids, suspended solids3, corrosive properties, radio!activity,

temperature range, foamability, etc.1%3 !,emi&al !,ara&teristi&s$ #hemical oxygen demand 1#.$.D.3, p:, acidity oral"alinity, hardness, total carbon, total dissolved solids, chlorine demand, "nown organicand inorganic components such as #l!, (%, ($0%!> , 7, 7b, #d, :g, #r, As, surfactants,phenols, hydrocarbons oils and greases.1-3 /io&,emi&al &,ara&teristi&s$ &iochemical oxygen demand 1&.$.D.3, presence ofpathogenic bacteria etc., and toxicity to man, aquatic organisms, plants and other lifeforms.The actual methods used for the treatment of a waste depend upon the characteristics ofthe particular waste.Suspended solids$The suspended solids are determined by filtering an aliquot of the

sample through a previously weighed sintered crucible or a tared 8ooch crucible anddrying the crucible at *+- +# to *+ +# to constant weight. The difference in weightindicated as mg2l gives the suspended solids content of the sample.Settlea"le solids$The settleable solids content of a sample is obtained by allowing * litreof the sample to settle for about * hour at %+ +# in an Imhoff cone, which is a taperedconical tube. The volume of settleable matter in the cone is recorded as ml2*. Thesettleable solids may also be expressed in mg2l which can be calculated by the differencebetween mg2l suspended solids minus mg2l non!settleable matter determined by theprocedure described as above.otal Solids$The total solids content of a sample is determined by evaporating a "nownvolume of the sewage or waste water sample, and drying the residue for %0 hours at *+-+# to *+ +#, followed by weighing. This gives the total solids content of the sample,which includes the dissolved as well as suspended solids.issolved o1%gen 2O3$The measurement of D$ gives a ready assessment of purity ofwater. The determination of dissolved oxygen is the basis of &$D 1&iochemical $xygenDemand3 test, which is commonly used to evaluate the pollution strength of waste waters.The determination of D$ content is also essential for maintaining aerobic conditions inthe receiving waters and also in the aerobic treatment of sewage and industrial wastewaters./io&,emi&al O1%gen emand 2/O3$ &iochemical oxygen demand represents thequantity of oxygen required by bacteria and other microorganisms during the biochemicaldegradation and transformation of organic matter present in wastewater under aerobicconditions. &$D test is a very valuable test in the analysis of sewage, industrial effluentsand grossly polluted waters. In spite of the inherent limitations, the &$D test is stillvalued as the best test for assessing the organic pollution. &$D is considered as the maEorcharacteristic used in stream pollution control. It gives very valuable informationregarding the purification capacity of streams and serves as a guide!line for theFegulatory Authorities to chec" the quality of effluents discharged into such waterbodies.

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prime importance that special preservation methods are used for samples that are not tobe analyBed immediately. This ensures that the characteristics to be analyBed are notchanged between collection and analysis. Table /.* gives special handling requirementsfor several wastewater characteristics.

a"le 8$# .reservation o' wastewater samples

.arameter .reservation met,od *a1imum

,olding period

&$D Fefrigeration at 0 +# 5 hours#$D % ml :%($02H days#olour Fefrigeration at 0 +# %0 hours#yanide p: of the sample raised to *+ or higher with a$: %0 hours6luoride one required days)etals o specific preservation, sample should be

acidified5 months

itrogen 19Eel!dahl, ammonia,nitrite3

Add 0+ mg, :g#l%2H> refrigeration at 0+

# days exceptfor 9Eeldahlnitrogen whichis unstable

7henol *.+ g #u($02H:-7$0to lower p: to less than 0>refrigeration at 0 +#

%0 hours

7hosphorus 0+ mg :g#l%2H> refrigeration at 0 +# days(ulphide % ml Binc acetate2H days$dour Fefrigeration at 0 +# daysTurbidity one available days#aliform

bacteria

(teriliBed bottle, no specific preservative,

refrigeration at 0 +#

-5 hours

The sample from industrial wastewaters should be representative of the industry. 6orexample, in case there are great variations in flow and2or characteristics, the samplingfrequency should be so adEusted as to obtain a representative sample. $ften, industriesfind it desirable to continuously monitor water quality of rivers and la"es which are usedas sources for water supply or for disposal of waste effluents. In the latter case,monitoring is done so that the quality and quantity of the discharge can be proportionedaccording to the assimilative capacity of the water body and for maintaining its qualitystandards. (everal municipalities also use continuous monitoring systems for theirtreatment facilities. )any continuous monitors are so sophisticated that not only the

analyses can be performed automatically and continuously, but also the analytical datacan be processed and translated by a computer for further use and application.

*E5OS OF ANA6SIS

'arious methods are available for analyBing wastewaters. These methods largely involvestandardiBed procedures that are often complicated and time!consuming. (ometimessimpler rapid methods can be substituted with little, if any, loss in either precision or

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accuracy. Test procedures often followed in practice are illustrated here briefly forspecific constituents. Detailed individual procedures are available in standard references.

EER*INAION OF ORGANI! *AER

issolved O1%gen 2O3(urface waters of good quality should be saturated with dissolved oxygen. A fall in D$level is one of the first indications that a water body is polluted by organic matter. TheD$ level in water depends on physical, chemical and biochemical activities prevailing inthe water body and, thus, it is one of the important parameters for assessing the purity ofthe water body. It is usually determined by Win"lerCs methods, which is based on thereaction of dissolved oxygen with manganese ions to form a precipitate of manganesedioxide. )n% $% J )n$%K 1/.*3The manganese dioxide is then treated with iodide ions when iodine is liberated in anamount chemically equivalent to the original dissolved oxygen.

)n$% %I

L

0:

J )n

%

I% %:%$ 1/.%3The liberated iodine is determined, usually by titrating it with sodium thiosulphate. %(%$- %L I% J (0$5%L %I L 1/.-3The presence of nitrites or iron in % oxidation state in the solution can interfere with theoriginal D$ determination. To eliminate these interferences, several modifications of thebasic method have been proposed. These include the use of aBide, permanganate and thealum to remove interferences due to nitrite, ferrous iron and suspended solids,respectively.The interference problems can also be overcome by using D$ analyBers with membraneelectrodes. The plastic membrane has the selective ability of allowing oxygen to diffusethrough but preventing interfering ions, such as nitrites. The dissolved oxygen, afterdiffusing through the membrane, reacts with the metal electrode and causes a cell currentwhich is directly proportional to the oxygen concentration in the sample. The analyBer iscalibrated by measuring, the D$ of a sample of "nown oxygen content, which isdetermined by the Win"ler method.

/io&,emi&al O1%gen emand 2/O3

The most widely used and accepted measure of biodegradable organic content ofwastewater is the !day, %+ +# &$D value. The brief analytical procedure is outlinedbelow

*. Two standard -++!ml &$D bottles are filled completely with the wastewaterof which the &$D is to be measured and the bottles are sealed.

%. $xygen content of one bottle is determined immediately.-. The other bottle is incubated at %+ +# for days in total dar"ness, after

which its oxygen content is measured.0. The difference between the two D$ values is the amount of oxygen that is

consumed by microorganisms during the days and is reported as the &$D,1!day &$D3 value of the sample.

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In practice, however, &$D measurements are more complicated than the simpleprocedure given above. The wastewaters may have a high oxygen demand, high enoughto deplete all the dissolved oxygen in the sample before the end of days, thus ma"ingthe test indeterminate. (o, often the sample is diluted with high purity water to preventtotal depletion of D$. The diluting water is made up of deioniBed water to which

appropriate nutrients, phosphate buffer, trace elements, and seed organisms 1usuallysettled domestic sewage3 are added. A blan" is run on the diluting water so that theoxygen demand of the seem material can be subtracted from the results. The &$D , iscalculated from the following equation

&$Ds 1in mg2H3 = DM N1D$t=0O D$t=53 O 1D$t=0O D$t=53P 1/.03 sample blan"where DM= dilution factor.When the standard !day2%+ +# conditions are used, approximately two!thirds of thecarbonaceous material is bro"en down> an incubation of about %+ days is needed fornearly complete brea"down. itrogenous nutrients can create problems in the &$D test.

&ecause of the slowness of the nitrification process, the oxygen demand of the nitrifyingbacteria is assumed to be negligible in the standard !day incubation period at %+ +#. Theactual environmental conditions of temperature, biological population, oxygenconcentration, etc., are impossible to reproduce in the test> hence, care must be exercisedin extrapolating the test results to the actual stream oxygen demands. In addition, manyindustrial wastewaters contain toxic materials which interfere with the growth ofmicroorganisms thus ma"ing the &$D test unreliable or even inapplicable without theaddition of suitable inoculum. (imilarly, the presence of algae in the wastewater affectsthe &$D test by leading to higher &$D values even when the test is performed indar"ness.The &$D analysis, despite its limitations, has been in use for many years for monitoringthe quality of stream pollution involving oxygen sag, but it is now being replaced by thechemical oxygen demand 1&$D3 test for research and plant control purposes.

!,emi&al O1%gen emand 2!O3

In the #$D test, the oxidiBing bacteria of the &$D test are replaced by a strong oxidiBingagent under acidic conditions. A sample of the wastewater containing organic material ismixed with an excess of potassium dichromate and sulphuric acid and the mixture isheated under total reflux conditions for a period of % hours. During digestion, thechemically oxidiBable organic material reduces a stoichiometrically equivalent amount ofdichromate, the remaining dichromate is titrated with standard ferrous ammoniumsulphate solution. The amount of potassium dichromate reduced gives a measure of theamount of oxidiBable organic material. Dichromate has advantages over other oxidants inoxidiBing power and applicability to a wide variety of samples.The #$D test does not distinguish between organic materials that are biodegradable andthose that are not, and, hence, gives a measure of the total oxidiBable organic material inthe sample. Due to this, the #$D test results are higher than those of &$D tests carriedout on the same sample. If inorganic substances such as chlorides and nitrites are presentin the wastewater, they interfore with the #$D test since they are also oxidiBed bydichromate and create an inorganic #$D that leads to an error in the measurement.

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#hloride interference can be eliminated by adding mercuric sulphate to the sample priorto the addition of other reagents, and nitrite interference can be overcome by addingsulphamic acid to the dichromate solution.

otal Organi& !ar"on 2O!3

Total organic carbon test is based on the oxidation of the carbon of the organic matter tocarbon dioxide, which is measured by a non!dispersive infrared analyBer. Alternatively,the carbon dioxide can be reduced to methane, which is then measured by a flameioniBation detector.In this test, a few micro!litres 1 to *+ Q*3 of the aqueous sample are inEected into acombustion tube containing a catalyst and heated to ;++4# in a constant flow of air.Water is vaporiBed and the carbonaceous matter is oxidiBed to #$%and steam. $utsidethe combustion tube, the steam is condensed and removed. #$ % is swept into a non!dispersive infrared analyBer, which measures the amount of #$ %. The concentration of#$%is directly proportional to the concentration of total carbon present in the originalsample and it includes both organic and inorganic carbon. Inorganic carbon can be

measured separately using an acid catalyst at *+

+

#, which is below the temperature atwhich organic matter is oxidiBed. $rganic carbon content can then be obtained bysubtracting the inorganic carbon from the total result. A flow diagram for a dualcombustion tube total carbon analyBer is shown in 6ig. /.*.The T$# test can be performed in a relatively short period of time 1few minutes3compared to &$D and #$D measurements and, hence, offers a valuable supplement to&$D and #$D estimations. &ecause of this advantage, an empirical correlation betweenT$# and #$D or &$D, that is specific to a particular plant operation, can be establishedand from this it is possible to obtain a tentative estimate of the plant performance quic"ly.

EER*INAION OF INORGANI! S7/SAN!ES

Nitrogen

The important chemical species containing nitrogen in wastewater systems are ammonia,organic nitrogen, nitrite and nitrate.Ammonia exists in aqueous solution as one of theintermediate compounds formed due to microbiological activity. itrogen, which is tiedup in high energy compounds such as amino acids and amines, is "nown as organicnitrogen.Gsually, organic nitrogen is a potential source of ammonia because deaminationreactions that occur during the metabolism of organic compounds release ammoniumions. These two forms of nitrogen are often combined in one measure, "nown as 9Eeldahlnitrogen.Aerobic decomposition eventually leads to nitrogen in the nitrite 1$ %O 3 and finallynitrate 1$-O 3 forms. 6or domestic wastewaters in G.(.A., the normal proportion ofnitrogen!containing compounds is relatively constant :0 +O5+R> organic nitrogen0+O;R> and nitrites and nitrates +OR. Although the contribution of nitrites andnitrates in domestic wastewaters is negligible, there may be a measurable concentrationof these ions following biological treatment due to the occurrence of nitrification. All theabove forms of nitrogen can be measured analytically by colorimetric techniques.

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9Eeldahl nitrogen is determined by digesting the sample in sulphuric acid when theorganic nitrogen is converted to ammonia.The total ammonia content is measured afterneutraliBing the excess sulphuric acid. The standard technique employed for thedetermination of ammonia is the essler methods. In this technique, the neutraliBedsample is first distilled to separate the ammonia from interfering substances. The

ammonia in the distillate is reacted with esslerCs reagent 1potassium mercuric iodide,9%:gI03, which produces a yellowish!brown colloidal dispersion. The colour intensity isdirectly proportional to the amount of :-present. The colour can be compared visuallyto standards or can be estimated photometrically.Another method of measuring the ammonia content in the sample is the phenol!hypochlorite method. In this method, ammonia is treated with phenol and hypochlorite inthe presence of a catalyst to produce the blue coloured solution of indophenol. Theintensity of colour is proportional to the ammonia concentration.Determination of nitrogen present as nitrite is based on the diaBotiBation of sulphanilicacid with nitrite followed by its combination with !1*!napthyl3!ethylenediaminedihydrochloride to form a purple aBo!dyes. The intensity of the purple colour is directly

proportional to the nitrite concentration and can be read on a photometer. The method isvery sensitive but is time consuming. A simple and rapid method consists of the additionof *,!dimethyl!%!phenyl!-!pyraBolone to the nitrite solution which forms a nitrosoderivative, the extinction coefficient of which can be measured spectrophotometrically.itrogen present as nitrate can be analyBed by reducing it to nitrite or ammonia, which isthen determined by employing one of the sensitive methods previously described. $nesuch method in popular use is the cadmium reduction method where the nitrates arequantitatively reduced by cadmium to nitrite. The nitrite thus produced is measured bythe diaBotiBation method. (ince this method gives the sum of nitrate and nitrite nitrogen,a separate analysis of the nitrite is required so that this value can be subtracted from theresults of the cadmium procedure. itrates can also be reduced to nitrites with Binc undercontrolled conditions and the nitrites determined colorimetrically. $ther techniques of thedetermination of nitrogen are the &rucine, phenoldisulphonic acid, and the chromotropicacid methods.

.,osp,orus

7hosphorus exists in wastewaters as orthophosphate 17$0-O , :7$0%O , :%7$0O 3,polyphosphate, and organic phosphate. $rthophosphates are assimilated by bacteriaduring their!growth process. :owever, polyphosphates must undergo enBymatichydrolysis to the ortho form before they can be assimilated. The organic phosphate ispresent in molecules. such as FA, DA and nucleotides. This is also an importantconstituent of industrial wastes.The orthophosphate is determined using colorimetric methods.These methods involvetreating the sample with ammonium molybdate under acidic conditions to formmolybdophosphoric acid, which is reduced using vanadium, or stannous chloride orascorbic acid when a coloured complex is formed. The intensity of the colour isproportional to the phosphate concentration in the solution. The vanadium method isquite useful for determining phosphate concentrations in the range of +.%O*/ mg. Thestannous chloride method is highly sensitive and concentrations as low as - Qg2H can be

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detected. The ascorbic acid method on the other hand is slightly less sensitive and theminimum detectable concentration is approximately %+ Qg2H.7olyphosphates are hydrolyBed into orthophosphates in an acidic medium and the excessacid is neutraliBed before the addition of ammonium molybdate solution. The amount ofpolyphosphate is obtained by subtracting the amount of orthophosphate originally present

in the sample from the result.The measurement of organic phosphorus is done by first oxidiBing the organic matter sothat phosphorus is released as phosphate ion.The total phosphorus can be measured bythe procedure previously outlined for orthophosphate and the amount of the organicphosphorus present is obtained by subtracting the inorganic content from the result.

ra&e Elements

The standard methods used for determination of toxic heavy metals li"e cadmium,chromium, lead and Binc are the atomic absorption spectrophotometry and colorimetry.The atomic absorption system consists of a light source which emits light of a particularwavelength, an atomiBer burner unit for introducing the sample into the flame, a prism to

separate and isolate the emission lines, and a detector. A schematic diagram of an atomicabsorption spectrophotometer is given in 6ig. /.%. In this technique, light from a sourcelamp of an exact wavelength necessary to excite the atoms of a particular trace elementtraverses the sample which is atomiBed in a flame, and passes through a prism where thedesired wavelength is isolated. The light intensity passing through the flame is reduced aslight is absorbed by each atom of the element> the amount absorbed is detected by thephotomultiplier tube. This decrease in intensity with the sample is a measure of theconcentration of the element. The technique is quite rapid, highly selective, andautomated for monitoring effluent streams. The detection limits for some selected toxicmetals are given in Table /.%.In using colorimetric method for determining the concentration of individual metals, caremust be ta"en to eliminate interference from other metals occurring simultaneously in thewaste sample. (ince metals form complex ions with organic matter present in wastewater,it is generally necessary to destroy the organic matter with acid digestion. Acid digestionalso eliminates possible interference from cyanide, nitrite, sulphide, sulphite, etc.Diphenylthio!carbaBone 1dithiBone3 is the colorimetric reagent used for the determinationof cadmium, lead and Binc. These metals give a red2pin" coloured complex whichcan be extracted in a suitable solvent such as carbon tetrachloride or chloroform. Thecolour intensity is then determined by a colorimeter or spectrophotometer. #hromiumdetermination involves oxidation of the metal to the hexavalent state and its reaction withdiphenylcarbaBide in acidic medium when a red!violet product is obtained whoseintensity can be measured photometrically.

Alalinit%

Al"alinity in wastewaters is due to the presence of bicarbonates, carbonates andhydroxides of metal ions such as calcium, magnesium, sodium and potassium. $f these,bicarbonates are most common, since they are formed by the action of carbon dioxide onthe basic materials such as the salts of calcium and potassium in the soil. In addition, saltsof wea" acids and ammonia present in wastewaters also contribute to the total al"alinity.

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Al"alinity is measured by titrating the sample with a standard acid such as 2+ : %($0>the results are expressed in terms of #a#$-.If the p: of the original sample is higherthan /.-, the titration is carried out using phenolphthalein indicator until it becomescolourless. This occurs at a p: value of /.-. This end point is "nown as phenolphthaleinal"alinity or bicarbonate equivalence point, which is observed in the case of hydroxide,

or carbonate, or both.Gsually, bicarbonates are present in the original sample along with hydroxides andcarbonates. In such cases the sample is titrated with methyl orange indicator and thetitration is carried out beyond the phenolphthalein end point. When a p: of about 0. isreached, there occurs a colour change from yellow to red indicating carbonic acidequivalence point. This result is used to calculate the total al"alinity, which may be due toany of the three al"aline ions, bicarbonates, carbonates or hydroxides.Determination of al"alinity is of importance in water softening, chemical treatment ofwastewater, corrosion control, and in removal of ammonia by air stripping.

.56SI!A !5ARA!ERISI!S

Suspended SolidsThe determination of suspended matter is extremely important in the analysis ofwastewaters. The suspended matter contained in domestic wastewaters and in manyindustrial wastes is largely organic and is, therefore, responsible for a significant portionof the oxygen demand. :ence, it is one of the maEor parameters used to evaluate thequality of domestic and industrial wastes.Analytically, the term total solids in wastewater refers to the matter that remains asresidue after evaporation and drying at *+- to *+ +#. The total solids can he classified asfilterable solids and suspended solids. The filterable solids are those that are able to passthrough a specified filter and consist of colloidal and dissolved solids. The colloidalsolids range in siBe from *+ !- to *+ !5 mm, while dissolved solids are smaller than *+!5 mmand exist as molecules and ions in solution. The suspended solids are retained on the filterand their minimum diameter is about * Qm. $f the suspended solids, the settleable solidsare those which settle in a cone shaped container 1Imhoff cone3 in a definite time period.The suspended solids 1also filterable solids3 may be further classified on the basis of theirvolatility at 5++ +#. The organic matter that is oxidiBed at this temperature is "nown as?volatile suspended solids? 1'((3, and the inorganic fraction that remains as ash istermed ?fixed suspended solids? or ?non!volatile suspended solids? 1'((3. 6ig. /.-gives an approximate classification of solids found in medium strength wastewaters.The suspended solids concentration is an easily measured parameter. In almost all thecases gravimetric methods are used such as filtration through a 8ooch crucible, but thedetermination is subEect to considerable error if proper precautions are not ta"en. Analternative procedure for measurement of suspended solids ma"es use of a continuousflow nephelometer. The measurement of light transmitted or light scattered by suspendedparticles can be correlated with the actual suspended solids concentration.

!olour and Odour

#olour and odour are important parameters from the standpoint of aesthetics. #olour maybe of organic or mineral origin. $rganic sources include algae, tannins, humiccompounds, etc.> inorganic sources are iron and manganese compounds, chemicals and

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dyes from various industries.$bEectionable odours in water are caused by algae anddecaying vegetation. (ome inorganic substances such as mercaptans, amines andsulphides also cause bad odour.#olour is measured by comparison with "nown standards. #oloured water made withpotassium chlorophtinate when tinted with cobalt chloride closely resembles colour of

many natural waters which are yellow!brownish in appearance. A stoc" solutioncontaining ++ mg2l of potassium chloroplatinate, with cobalt chloride added as a tintingmaterial, is usually prepared and this is assigned colour of ++ units. Then a series ofwor"ing standards is prepared from it by dilution.The intensity of colour in water ismeasured against these standards by direct visual comparison.(uspended matter in water can interfere with the measurement of colour. In such casesthe sample is centrifuged to separate the solids and analysis is made on the clear portion.Femoval of the suspended matter from the sample by filtration is not recommendedbecause of the possibility that the filter may adsorb some colour and thereby cause errorin the measurement.The odour causing substances are usually present in very small quantities and are often

very complex. It is, therefore, often impossible and impractical to isolate and identifypositively the odour causing materials. Svaluation of odour is, thus, dependent on theolfactory senses of the tester and on his ability to distinguish between different levels and"inds of odours. The testing is based entirely on arbitrary comparison since no absoluteunit or base exists for odour.The standard test method is the threshold dilution method in which the odour bearingsample is diluted successively with odour!free water, until a dilution is obtained whichhas a barely perceptible odour. The result is expressed in terms of the ?threshold odournumber 1T$3?, which is given by, ml of sample ml odour!free water T$ = !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ml of sampleIt has been recommended that odour tests be run at 0+ and 5+ +#. (ince T$ is a functionof temperature, the test temperature should be reported in all cases.

/A!ERIOOGI!A *EAS7RE*ENS

6rom public health standpoint the bacteriological quality of water is as important as thechemical quality. A variety of procedures have been devised to measure thebacteriological quality, but the most popular method is based on determining the contentof ?indicator organisms? in it. The principal indicator organisms used are the coliformgroup of bacteria.This group is normally nonpathogenic, present in polluted waters whenpathogens are, or might be present, unable to multiply under conditions when pathogensdo not multiply, and readily identified and enumerated by simple laboratory techniques.The coliform group of bacteria has the ability to ferment lactose or lauryl tryptose brothand produce gas. This offers a simple test of the presence of coliform organisms.:owever, some other organisms also ferment the broth under certain conditions and,therefore, additional growth reactions must be carried out to confirm the presence ofcoliform group. The test is conducted by inoculating the broth by multiple portions ofa series of decimal dilutions of the water sample. The result is usually expressed as thenumber of coliform organisms per unit volume of the sample.

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Two methods are generally used for obtaining the number density of coliform organismsin the test sample. $ne is the memrobrane!filter technique and the other is the mostprobable number 1)73 technique.In the membrane!filter technique, a "nown volume ofwater sample is passed through the filter that has a very small pore siBe. The coliformbacteria are captured .by the filter and the filter is then exposed to nutrients which

promote the growth of coliform while inhibiting that of other organisms. After %0 or 0/hours of incubation, the number of coliform colonies is counted and their density isdetermined. The caliform colonies appear pin"ish in colour and their count is made withthe aid of an optical device. The coliform density is reported in terms of 1total3 coliformsper *++ ml.The most probable number of coliform organisms is a statistical estimate of their densityand is based on the examination of a number of portions of different siBes of the watersample for the presence of coliforms. 6rom a "nowledge of the number of portions ofdifferent siBes giving positive or negative results for coliforms, the )7 can bedetermined from the following equation*-,6rom the above result, the most probable number is +.0 per mi at which a is maximum.

In other words the )7 per *++ ml is 0.Although the coliform bacteria meet some of the criteria for indicator organisms, they dohave certain limitations. #oliforms often grow in treatment facilities or water bodies andthe tests can reveal higher populations even though pathogens are far less li"ely tomultiply under the same environmental conditions. In addition, some viruses and severalother organisms may survive for longer periods than coliforms, and reduction ofcoliforms to low concentrations or even to Bero may not always indicate that the water issafe. evertheless, in spite of these and other limitations, the coliform test has provided avaluable and reliable technique for evaluating water purity.

WAER 97AI6 SANARS

The analyses required of water samples depend on the intended use of the water. 6orexample, if its intended use is drin"ing, water should meet certain quality criteria withrespect to the appearance 1turbidity, colour3, potability 1taste, odour3, health 1bacteria,nitrates, chlorides, etc.3 and toxicity 1metals, organics3. These and similar criteria areestablished by health or other regulating agencies to ensure that the water quality in aresource is suitable for the proposed use.&ased on the criteria, quality standards are set, which reflect the current state of"nowledge of various water constituents. These standards are continuously revised asmore and more is learnt about the effects of water constituents on proposed uses. :ence,these standards should not be used as absolute limits, but only as guidelines that can beused for preliminary Eudgements. Table /.- summariBes several quality criteria and theirstandards for drin"ing water as suggested by the following agencies

1*3 Indian #ouncil of )edical Fesearch 1I#)F31%3 World :ealth $rganiBation 1W:$31-3 Gnited (tates 7ublic :ealth (ervice 1G(7:(3

(tandards have been prepared for raw waters to be used as a source for various industrialapplications. The specific purpose for which the water is used usually controls therequisite water quality. Water used in food and beverage industries will need to meetstandards similar to those for drin"ing water, while water for cooling purposes can

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contain much higher concentrations of impurities. Table /.0 illustrates the water qualitycharacteristics of raw surface waters that have been used as source for various industrialoperations. The values listed are the maximum concentrations of different constituents inthe raw surface waters used in the specified industry, and not the maximumconcentrations that could be tolerated.

Table /.-Table /.0

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)$ Wastewater treatment

$rigin of wastewater N-, p.%/%P> #haracteriBation of wastewaters N*, p.+P>Wastewater sampling and methods of analysis N-, p.-*-P> )ethods and equipmentused in wastewater treatment 7reliminary treatment> 7rimary treatment1sedimentation, coagulation, equaliBation, neutraliBation3 N%, *P>. (econdary

1&iological3 treatment 1aerobic aerated lagoons, tric"ling filters, activated sludgeprocess, oxidation ditch process, oxidation pond> anaerobic sludge digestion, sludgetreatment and disposal3 N%,*P, (ludge treatment and disposal N-P> Advanced or tertiarytreatment 1evaporation, ion exchange, adsorption, chemical precipitation,electrodialysis, electrolytic recovery, reverse osmosis3 N%,*P, Fecovery of materialsfrom process effluents N-P.

/oo Re'eren&e

*. Snvironmental chemistry and pollution control, (.(. Dara, p. +!/.%. Waste water treatment, ).. Fao and A.9. Datta, 7. *;.-. Snvironmental pollution control engineering, #.(. Fao, p. %/%!%/, -*-!-%.

:$ Wastewater 'rom some t%pi&al industries 1Wastewater sources, characteristics,effects and treatment options3 7ulp and paper, tanneries, fertiliBer, sugar industry,pharmaceuticals, textile, soap and detergent manufacturing, chloro!al"ali industry,iron and steel manufacturing, thermal and nuclear power plants, photochemicalindustry.

1Wastewater sources> characteristics> effects and treatment options3

/oo Re'eren&e

*. Waste water treatment, ).. Fao and A.9. Datta, 7. *;.

)ultichoice questions> True2 6alse questions/oo Re'eren&e

*. Snvironmental chemistry, &. 9. (harma, p. water pollution !0*.

;$ #urrent industrial environmental status.8uidelines and discharge standards of variousindustries permit system for discharge2emission. 7rocedures for underta"ing SIA andtheir evaluation.

/oo Re'eren&e

*. Snvironmental management SIA, (.(. Dara, p. %*

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--------------------------------

!,apter )< Wastewater treatment 1#( Fao -, p. --- 3

/ASI! .RO!ESSES OF WAER REA*EN

The purpose of wastewater treatment is to remove the contaminants from water so that

the treated water can meet the acceptable quality standards. The quality standards usuallydepend upon whether water will be reused or discharged into a receiving stream.Available wastewater treatment processes can be broadly classified as physical, chemicalor biological. These processes, which consist of a series of unit operations, are applied indifferent combinations and sequences depending upon the prevailing situations ofinfluent concentration, composition and condition and specifications of the effluent.7hysical processes are based on exploitation of the physical properties of thecontaminants and are generally the simplest forms of treatment. These principallycomprise screening, sedimentation, flotation and filtration. #hemical processes utiliBe thechemical properties of the impurities or of the added reagents. #ommonly used chemicalprocesses are precipitation, coagulation, and disinfection. $ther physical and chemical

processes such as air stripping, carbon adsorption, oxidation and reduction, ion exchangeand membrane processes li"e reverse osmosis and electrodialysis are also important incertain particular cases. &iological processes utiliBe biochemical reactions> typicalexamples are biological filtration and the activated sludge process.The wastewater treatment processes are generally grouped according to the water qualitythey are expected to produce. These processes are usually grouped as the primarytreatment, the secondary treatment, and the tertiary or the advanced waste treatment.7rimary treatment removes identifiable suspended solids and floating matter. In thesecondary treatment, also "nown as the biological treatment, organic matter that issoluble or in the colloidal form is removed. Advanced waste treatment may involvephysical, chemical or biological processes or their various combinations depending on the

impurities to be removed. These processes are employed to remove residual soluble non!biodegradable organic compounds, including surfactants, inorganic nutrients and salts,trace contaminants of various types, and dissolved inorganic salts. The advanced wastetreatment processes are expensive, and are used only when water produced is required tobe of higher quality than that produced by conventional secondary treatment so that thetreated water can be reclaimed and put to some form of direct re!use.

!,apter 4< Wastewater treatment o' various industries

IN7SRIA WASE REA*EN

=$0$ Introdu&tion the restfinds its way into the water courses as waste water. Thus the industries Eoin themunicipalities to contribute to the ?pollution? of the natural bodies of water.The industrial wastes either Eoin the streams or other natural water bodies directly, or areemptied into the municipal sewers. Thus these wastes affect in some way or other, thenormal life of a stream or the normal functioning of sewerage and sewage treatmentplants. )uch attention is now given in India on the treatment of industrial wastes, due to

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its growing pollution potential arising out of the rapid industrialiBation of the country.(treams can assimilate certain amount of wastes before they are ?polluted?, and themunicipal sewage treatment plants can be designed to handle any "ind of industrialwastes. Thus we have three alternatives for the disposal of the industrial wastes viB 1i3The direct disposal of waste into the streams without any treatment, 1ii3 discharge of the

wastes into the municipal sewers for combined treatment, and 1iii3 separate treatment ofthe industrial wastes before discharging the same into the water bodies. The selection of aparticular process depends on various factors li"e the following 1i3 (elf purification capacity of the streams, 1ii3 7ermissible limits of the pollutants in the water bodies, established by law,1Tolerance limits for the inland surface waters, subEected to pollution, as given by I(I areshown in Table *.-3 1iii3 Sconomic interests of both the municipalities and the industries, 1iv3 Technical advantages, if any, in mixing the industrial wastes with domesticsewage. After a thorough economic and technical appraisal, if it is decided to treat theindustrial waste either independently or along with the domestic sewage, the treatment

plants are to be designed after 1i3 a thorough investigation of the characteristics of thewastes, and 1ii3 a cost study for the final choice of the particular method of treatment.

=$#$ !,ara&teristi&s o' t,e Industrial Wastesuipment used in Waste Water reatment 2ara p$ ?(3#

The various methods used in sewage and industrial waste water treatment are as follows

2i3 .reliminar% reatment$

The principal obEectives of preliminary treatment are the removal of gross solids 1i.e.large floating and suspended solid matter, grit, oil and grease if they are present inconsiderable quantities.Harge quantities of floating rubbish such as cans, cloth, wood and other larger obEectspresent in waste water are usually removed by metal bars, acting li"e strainers as thewaste water moves beneath them in an open channel. The velocity of the water is then

reduced in a grit!settling chamber of a larger siBe than the previous channel.Femoval of gross solids is generally accomplished by passing waste water through mixedor moving screens. Different types of these screens are available, which include barscreens 1described above3, hand ra"ed or mechanical ra"ed screens, drum screens andwire rope screens.The modern mechanical screens cum filters include rotary, self!cleaning, gravity typeunits and circular overhead fed vibratory units. These are costlier, as compared to theconventional bar screens, but are very effective in reducing the suspended solids and

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&$D. (ometimes, instead of screening, the gross solids in the sewage are cut into smallpieces with the help of macerators or comminutors.8rit 1or detritus3 is removed in the early stages of treatment in grit channels or tan"s tosafeguard against any damage to pumps and other equipment by abrasion and also toavoid settling in pipe bends and channels. 8rit, being heavier than organic solids, can be

separated from organic solids by careful regulation of the flow velocity in the grit tan"s.The grit settling chambers are periodically disconnected from the main system to removethe grit manually, for possible use in land!filling, road ma"ing and on sludge drying beds.If the waste waters contain appreciable quantities of oil and grease, then it is advisable toremove as much of these as possible, in the preliminary treatment itself to avoid adverseeffects on the rest of the plant. This is achieved by passing the waste water throughs"imming tan"s where oil and grease are s"immed off. This process can be renderedmore efficient by aeration, chlorination or vacuum flotation.If the oil and grease are in emulsified condition, as in wool!scouring wastes, ordinarys"imming methods are ineffective. In such cases, they may be removed with the help ofchemical reagents in primary sedimentation tan"s.

2ii3 .rimar% reatment

After the removal of gross solids, gritty materials and excessive quantities of oil andgrease, the next step is to remove the remaining suspended solids as much as possible.This step is aimed at reducing the strength of the waste water and also to facilitatesecondary treatment.Sedimentation$The suspended matter can be removed efficiently and economically bysedimentation. This process is particularly useful for treatment of wastes containing highpercentage of settleable solids or when the waste is subEected to combined treatment withsewage.The clear liquid produced is "nown as the overflow and it should contain no readilysettleable matter. If the sedimentation tan" is poorly designed the overflow may containsolid particles or the underflow may be more dilute than desired.The sedimentation tan"s are designed to enable smaller and lighter particles to settleunder gravity. The most common equipment used include horiBontal flow sedimentationtan"s and centre!feed circular clarifiers. The settled sludge is removed from thesedimentation tan"s by mechanical scrapping into hoppers and pumping it outsubsequently. In a well!designed continuous flow sedimentation tan", about +R of thesuspended solid matter is settled out within two hours of detention time. An efficientsedimentation system is expected to remove about ;+R of the suspended solids and 0+Rof organic matter 1thus reducing the &$D3.In waste waters containing larger proportion of industrial wastes, a long detention timehelps in mixing and balancing 1or equaliBing3 of the various wastes and safeguardsagainst unduly heavy loads being passed on to the biological purification plantssubsequently.Sedimentation aids$6inely divided suspended solids and colloidal particles cannot beefficiently removed by simple sedimentation by gravity. In such cases, mechanicalflocculation or chemical coagulation is employed.InMechanical flocculation, the wastewater is passed through a tan" with a detention timeof -+ minutes and fitted with paddles rotating at an optimum peripheral speed of +.0-

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m2s. Gnder this gentle stirring, the finely divided suspended solids coalesce into largerparticles and settle out. (pecialised equipment such as Clariflocculator is also available,wherein flocculating chamber is a part of a sedimentation tan".In chemical coagulation, the sewage or other waste water is treated with certainchemicals which form a floc 1flocculent precipitate3 that absorbs and entrains the

suspended and colloidal particles present. The coagulants in common use are 1*3:ydrated lime 1%3 Alum, Al%1($03%V*/:%$ 1-3 #opperas 6e($0.:%$ 103 6erric chlorideand 13 #hlorinated copperas, 6e($0.#l 1mixture of ferric sulphate and chloride3. Alum isthe most popular coagulant used both in water and waste water treatment. 6or bestresults, the chemicals used for coagulation are well mixed with the wastewater in baffledchannels followed by mechanical flocculation before sedimentation. 7re!aeration forabout *+ minutes before sedimentation is also found to help in the removal of entertainedgases li"e #$%and :%( and improved flocculation and separation of oil and grease.#oagulation is the most effective and economical means to remove impurities.(ometimes, in addition to the coagulants, other chemicals called "coagulant aids" arealso used in very small quantities to promote the formation of large and quic" settling

floc and thereby enhancing coagulation. Activated silica and polyeletrolytes 1such aspolymers of cyanamide, acrylic or methacrylic acids and their derivatives, andhydrolysed high molecular weight polymers having molecular mass of *+0 to *+5 ofacrylamide or acrylonitrile3 are the most commonly used coagulant aids. 7olyelectrolytesare generally used in dilute solutions 1+.% ppm3. $wing to their selective property, careshould be ta"en in selecting the most suitable polyelectrolytes.The synthetic coagulant aids wor" by the following two mechanisms1i3 The coagulant aids, having long chain molecular structure, are absorbed on two or

more particles, thus drawing them together.1ii3 &y reducing the charge on the particles and thus reducing the repulsive power of the

li"e charges on the particles.The sequence of operations in the chemically aided coagulation are 1a3Addition of lime,if there is no sufficient al"alinity, 1b3Addition of coagulants, followed by rapid mixingfor 0 to 5 minutes, 1c3Addition of coagulant aids, followed by gentle agitation or slowstirring for about 0+ minutes.

Flotation

6lotation may be used in place of sedimentation, primarily for treating industrialwastewaters containing finely divided suspended solids and oily matter. 6lotationtechnique is used in paper industry to recover fine fibres from the screened effluent and inthe oil industry for the clarification of oil!bearing waste. It is also used for treatingeffluents from tannery, metal finishing, cold!rolling, and pharmaceutical industries. Anincreasingly important application is the thic"ening of the sludge obtained from activatedsludge process.7articles of density very close to that of water are very difficult to settle in normalsedimentation tan"s and ta"e a long time for separation. In such cases, the separation canbe speeded up by aerating the effluent whereby air bubbles are attached to the suspendedmatter. This has the effect of increasing the buoyancy of the particles> as a result, theparticles float to the surface where they can be readily removed. To aid in the flotationprocess, chemical coagulants such as aluminium and ferric salts or polymer coagulant!

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aids are often used. These chemicals increase the flocculent structure of the floatedparticles so that they can easily entrap the air bubbles.The residence time in the flotation tan" is about half an hour.

E>ualiation$ (ome industries produce different types of wastes, having different

characteristics at different intervals of time. :ence, uniform treatment is not possible. Inorder to obviate this problem, different streams of effluents are held in big holding tan"sfor specified periods of time. Sach unit volume of waste is mixed thoroughly with otherunit volumes of other wastes to produce a homogeneous and equaliBed effluent. Aerationor mechanical agitation with paddles usually give better mixing of the different unitvolumes of effluents.

Neutraliation$:ighly acidic or highly al"aline wastes should be properly neutraliBedbefore being discharged. Acidic wastes are usually neutraliBed by treatment with limestone or lime!slurry or caustic soda, depending upon the type and quantity of the waste.Al"aline wastes may be neutraliBed by treatment with sulphuric acid or #$ % or waste

boiler flue gas.If both acidic and al"aline wastes are produced in the same plant or at nearby plants,storing them in separate holding tan"s and mutual neutraliBation by mixing them inappropriate proportion is the cheapest method.

SE!ONAR 6 2/IOOGI!A3 REA*EN

(o far, only those materials were considered that might be removed by some type ofphysical or mechanical action. (ince much of the organic material in wastewater may becolloidal or dissolved, the primary treatment processes are largely ineffective in removingit. This organic material still represents a high demand for oxygen which must be reducedfurther so that the effluent may be rendered suitable for discharge into the water bodies.In secondary treatment, the dissolved and colloidal organic matter present in waste watersis removed by biological processes involving bacteria and other micro!organisms. Theseprocesses may be aerobic or anaerobic. In aerobic processes, bacteria and other micro!organisms consume organic matter as food. They bring about the following sequentialchanges

i3 #oagulation and flocculation of colloidal matter,ii3 $xidation of dissolved organic matter to #$%, andiii3 Degradation of nitrogenous organic matter to ammonia, which is thenconverted into nitrite and eventually to nitrate.

Thus, secondary treatment reduces &$D. It also removes appreciable amounts of oil andphenol. :owever, commissioning and maintenance of secondary treatment systems areexpensive.&iological or secondary treatment, as it is commonly referred to, is very similar inconcept to the natural biodegradation of organic matter by aerobic bacteria. In biologicaltreatment, oxygen supplied to the bacteria is consumed under controlled conditions sothat most of the &$D is removed in the treatment plant rather than in the watercourse.Thus, the principal requirements of a biological waste treatment process are an adequateamount of bacteria that feed on the organic material present in wastewater, oxygen, andsome means of achieving contact between the bacteria and the organics.

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Two of the most commonly used systems for biological waste treatment are the activatedsludge system and biological!film system. In the activated sludge system the wastewateris brought into contact with a diverse group of microorganisms in the form of a flocculentsuspension in an aerated tan". Whereas in the biological!film system, also "nown astric"ling filters, the wastewater is brought into contact with a mixed microbial population

in the form of a film of slime attached to the surface of a solid support medium. In bothcases the organic matter is metaboliBed to more stable inorganic forms. The most popularmeans of treating domestic sewage has been the biological!film system because of itsease of operation. :owever, the activated sludge process is gaining popularity and ispreferable to the biological!film system because of its reliability and suitability forhandling large volumes of wastewater, and because of the high degree of treatmentachieved.The effluent from primary sedimentation tan"s is first subEected to aerobic oxidation insystems, such as aerated lagoons, tric"ling filters, activated sludge units, oxidationditches or oxidation ponds. Then the sludge obtained in these aerobic processes, togetherwith that obtained in the primary sedimentation tan"s, is subEected to anaerobic digestion

in the sludge digesters.#ertain micro!organisms, in presence of dissolved oxygen and in proper environmentalconditions, utilise organic waste as their food, and convert into simpler compounds suchas #$%, :%$, nitrates and sulphates which are non!pollutants. This process, therefore, canbe used to remove organic substances from wastes. Almost all organic substances, with afew exceptions, such as hydrocarbons and ethers, can be oxidised by aerobic biologicaltreatment. #omplex cell tissues and protein materials are also synthesiBed during thisprocess, which are then agglomerated and removed from the waste by settling.8ermicidal and resistant organics, such as cyanides and phenols also can be destroyed byspecial types of micro!organisms, after prolonged acclimatiBation periods.Gnder anaerobic conditions 1i.e., in the absence of dissolved oxygen or gaseous oxygen3,certain groups of micro!organisms, e.g., hydrolyte and methane forming organisms, cancarry out the digestion of complex organic wastes. The hydrolyte organisms convertcomplex organic compounds to simple and low!molecular weight organic acids andalcohols. These are then converted by methane bacteria to #$ % and #:0. Anaerobictreatment process can be carried out in depth without the need for large surface area. Itcan ta"e place in mixed or enriched cultures and can, therefore, be maintained easily onlarge scale. The process can be applied to most types of substrates excepting a few li"elignin and mineral oil. The process is less expensive but the final effluent is lesssatisfactory, as compared to that from aerobic treatment, because of the dar" colour,odour and higher residual &$D.Anaerobic treatment is mainly employed for the digestion of sludges. :owever, organicliquid wastes from dairy, slaughter house etc., were treated by this method economicallyand effectively. The efficiency of this process depends upon p:, temperature, wasteloading, absence of oxygen and toxic materials.(ome of the commonly used biological treatment processes are described below

2i3 Aerated agoons$These are large holding tan"s or ponds having a depth of -! mand are lined with cement, polythene or rubber. The effluents from primary treatmentprocesses are collected in these tan"s and are aerated with mechanical devices, such as

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floating aerators, for about % to 5 days. During this time, a healthy flocculent sludge isformed which brings about oxidation of the dissolved organic matter. &$D removal tothe extent of ;+R could be achieved with efficient operation. The operation andmaintenance are relatively simple. The maEor disadvantages are the larger spacerequirements and the bacterial contamination of the lagoon effluent which necessitates

further biological purification in maturation pond or by secondary sedimentation andsludge digestion.

2ii3 ri&ling Filters$The tric"ling filters usually consist of circular or rectangular beds,* m to - m deep, made of well!graded media 1such as bro"en stones, 7'#, coal, co"e,synthetic resins, gravel or clin"ers3 of siBe 0+ mm to *+ mm, over which wastewater issprin"led uniformly on the entire bed with the help of a slowly rotating distributor 1suchas a rotary sprin"ler3 equipped with orifices of noBBles. Thus, the waste water tric"lesthrough the media. The filter is arranged in such a fashion that air can enter at the bottom,counter current to the effluent flow and a natural draft is produced. A gelatinous film,comprising of bacteria and aerobic micro!organisms "nown as ?Uooglea?, is formed on

the surface of the filter medium, which thrive on the nutrients supplied by the sewage orthe waste water. The organic impurities in the waste water are adsorbed on the gelatinousfilm during its passage and then are oxidised by the bacteria and the other micro!organisms present therein. When the thic"ness of the film on the medium increases, a partof it gets detached and carried away along with the effluent. :ence, the effluent from thetric"ling filters is allowed to settle in a settling tan" to retain the sludge particles and isthen discharged. The sludge is then pumped to the sludge digestion unit.A (chematic representation of a typical Tric"ling filtration process is given in 6ig. /.

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Although tric"ling filtration is classified as an aerobic process, it is indeed a facultativesystem. Aerobic bacterial species, e.g., spore forming bacteria and bacillus are mostlypresent in the upper layer of the filter, whereas anaerobic species, such as Desulfo vibrio,are present in the interfaces of the stones. 6acultative bacteria, such as 7seudomonas,Alerligens, 6lavo bacterium, Snterobactericeae and )icrococcus are also present in the

tric"ling filters. Algae, fungi, ciliates, protoBoan, worms, senils, insect larvae that feed onmicro!organisms are also present.&y and large, smaller media give better results but they tend to cho"e easily. (yntheticplastic media are found to be particularly useful for industrial wastes of higher loading.)oreover, they can afford maximum surface area for the formation of microbial film andtheir light weight helps in greater economy in laying the underdrain of the filter.The microbial film formed is very sensitive to temperature. The metabolic activity isproportional to the temperature of the waste water passing through the filter. Thus, theefficiency of the filter decreases in winter season.The efficiency of the filter depends upon the composition of the waste, strength ofhydraulic loading, temperature, p:, depth of the filter, the siBe and uniformity of the filter

medium, uniformity of waste water distribution over the filter and proper air supply.The tric"ling filter has greater resistance to toxic waste, as compared to the ?Activated(ludge 7rocess? and can recuperate more promptly from an overdose of toxic materials.:owever, shoc" loads or sudden surges should be avoided lest the efficiency of the filtermight be impaired temporarily or even permanently.Tric"ling filters are simple to operate and can produce &$D removal to the extent of 5to /R, depending upon the rate of filtration. )oreover, constant manual attention is notneeded for this process. Tric"ling filters produce effluents of consistent and better quality.The disadvantages of the process include the cost of construction and the need forventilation ducts for the under drain system. The efficiency decreases with increasedloading of the waste water. To overcome this problem, the waste water may be dilutedwith the effluent from the previous treatment.Tric"ling filters are effectively used for the treatment of industrial wastes from dairy,distillery, brewery, cannery, food processing, pulp and paper mills, pharmaceuticals,petrochemicals, slaughter house and poultry processing industries.

2iii3 A&tivated Sludge .ro&ess

This is the most versatile biological oxidation method employed for the treatment ofwaste water containing dissolved solids, colloids and coarse solid organic matter. Theprocess flow diagram for a typical activated sludge plant is given in 6ig. ;.*0. Theessential features of the process are an aeration stage, solids!liquid separation followingaeration, and a sludge recycle system. Wastewater after primary treatment enters anaeration tan" where the organic matter is brought into intimate contact with the sludgefrom the secondary clarifier. This sludge is heavily laden with microorganisms which arein an active state of growth. Air is introduced into the tan", either in the form of bubblesthrough diffusers or by surface aerators. The microorganisms utiliBe the oxygen in the airand convert the organic matter into stabiliBed, low!energy compounds such as $-, ($0,#$%, and synthesiBe new bacterial cells. The effluent from the aeration tan" containingthe flocculent microbial mass, "nown as the sludge, is separated in a settling tan",sometimes called a secondary settler or a clarifier. In the settling tan" the separated

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sludge exists without contact with the organic matter and becomes activated. A portion ofthe activated sludge is recycled to the aeration tan" as a seed> the rest is wasted . If all theactivated sludge is recycled, then the bacterial mass would "eep increasing to the stagewhere the system gets clogged with solids. It is, therefore, necessary to ?waste? some ofthe microorganisms, and this wasted sludge is the one which is processed and disposed.

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The micro!organisms should be provided with essential nutrients, such as and 7, whichare supplied in the form of urea and mono!or di!ammonium hydrogen phosphate. $thernutrients, e.g., 9, )g, #a, etc are generally present in the waste. $ther important factorswhich determine the efficiency of the activated sludge are p:, temperature and oxidation!reduction potential. The optimum p: range for the process is 5. to ;.+. How temperature

slows down the rate of metabolism, while high temperature increases the metabolicactivity to such an extent that the oxygen is consumed fast, leading to anaerobicconditions.Activated sludge process produces a high quality effluent with relatively small areas. Anefficient aeration for - to 5 hours is adequate for sewage, whereas for industrial wastes, 5to %0 hours of aeration is required for this process. With efficient systems, about ;R&$D removal is possible. The disadvantages include high cost of operation andmaintenance, need for careful attention and sensitivity to shoc" loads of toxic and organicsubstances.Activated sludge process was used satisfactorily for the treatment of effluents from foodprocessing, sugar, textile processing, antibiotic manufacturing industries, etc.

E''i&ien&ies o' A&tivated Sludge .ro&ess

The activated sludge process, including pretreatment and primary settling, is an efficientmeans of removing suspended solids and organic matter from wastewaters. Table ;.-presents typical primary and secondary effluent characteristics. As is seen from the table,most of the suspended solids and the &$D materials are removed after secondarytreatment. :owever, the activated sludge process does a poor Eob in removing bothnitrogen and phosphorus from wastewater. The total nitrogen content is reduced byapproximately one!third. The influent ammonia is oxidiBed by nitrifying bacteria and thisreduction is partially balanced by the production of ammonia by the sludge mass. The netresult is that there is a slight reduction in the ammonia concentration.

Table ;.- Wastewater characteristicsM

Typical wastewater1mg2l3

7rimary effluent1mg2l3

(econdary effluent1mg2l3

(uspended slids %-+ / %+&$D %++ *- %+Ammonia nitrogen */ *5 *Total nitrogen -+ % %+7hosphorus *- ** *+Gltimate oxygen demand -/- %5 ;;

M&ased on average treatment efficiencies. These values may vary from plant to plant, andwithin any one plant with time.

7rimary sedimentation in conventional treatment settles only a small percentage of thephosphorus present in wastewater, since its maEor part is dissolved. In the activatedsludge process the microbial floc ta"es the soluble phosphate as a nutrient but theremoval efficiency is small 1less than -+R3, so that most of the phosphorus remains

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uneffected by the secondary treatment. The ultimate oxygen demand 1G$D3 is reducedby about R in the conventional secondary treatment. )ost of this reduction is due tothe oxidation of the organic carbonaceous material and the remainder is due to removal ofammonia. The extended aeration process may be expected to raise the removal efficiencyof G$D to about ;+R.

Table ;.0 gives the maEor differences between conventional tric"ling filters and activatedsludge systems, and also lists their advantages and disadvantages.

a"le =$4 !omparison o' tri&ling 'ilters wit, a&tivated sludge s%stems

Tric"ling filters Activated sludge systems*. &acterial growth is fixed on the media &acterial growth is suspended as a

dispersed floc%. All solids from the settler are wasted (olids from the settler are partially

recycled-. Hess sensitive to shoc" loading, more

stable

)ore sensitive to shoc" loadings, require

closer process control0. 7roduce insects and odours 7roduce spray clouds. Hess effective in removing disease!

causing organisms)ore effective in removing pathogensthan tric"ling filters

5. How operating costs :igh operating costs

2iv3 O1idation it&,$This can be considered as a modification of the conventionalActivated (ludge process. $xidation ditch 16ig. *+3 usually consists of an oval shapedcontinuous channel, about * to % m deep and lined with plastic, tar or butyl rubber. Wastewater, after screening or comminution in the primary treatment, is allowed into theoxidation ditch. The mixed liquor containing the sludge solids 1)H((3 is aerated in the

channel with the help of mechanical rotors. Honger retention times are needed. The usualhydraulic retention time is *% to %0 hrs and for solids, it is %+!-+ days. )ost of the sludgeformed is recycled for the subsequent treatment cycle. The surplus sludge can be driedwithout odour on sand drying beds.The maEor advantages of the oxidation ditch include simplicity in operation, easymaintenance, low cost of construction, operation and maintenance, overall efficiency andflexibility. This process is generally used for wastes having low &$D.$xidation ditch process is used effectively for the treatment of waste water from beet!sugar manufacture, vegetable and fruit canning industry, slaughter house and meatpac"ing industry and edible oil refineries.

2v3 O1idation .ond$An oxidation pond is a large shallow pond 1+. m to *. m depth3with arrangements to measure the inflow and outflow. The wastes enter the pond at oneend and the effluent is removed at the other end. (tabiliBation of organic matter in thewaste is brought about mostly by bacteria, such as 7seudmonas, 6lavo bacterium andAlcaligenes, and to some extent by flagellated protoBoa. The oxygen requirement fortheir metabolism is provided by algae present in the pond. The algae, in turn, utiliBe the#$%released by the bacteria for their photo synthesis. $xidation ponds are also calledwaste stabiliBation ponds.

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fuel to provide the heat required to warm the digestion tan"s. In large installations, it canbe used for power generation.103 Although anaerobic treatment is a slow process, it is useful for treating smallquantities of wastes, containing readily oxidisable dissolved organic solids in liquid formor in finely divided form. The operation and maintenance costs are lesser with this

treatment. That is why some liquid wastes containing soluble organics from dairy,slaughter house and paper mill industries have been economically and effectively treatedby this process.

Sludge reatment and isposal

:andling and disposal of sludge from biological wastewater treatment plants is animportant problem and represents about half the cost of most sewage treatment plants.The concentration of solids in the primary sewage sludge is about R> the activatedsludge contains less than *R solids> and the sludge from tric"ling filters has about %Rsolids. This means that the sludge is composed almost entirely of water and volumereduction is the "ey to economic disposal. In addition to reducing its high water content,

the sludge must be stabiliBed so that its biological activity and tendency towardsputrefaction are reduced drastically.

6ig. ;.%0 (equence of operations for sludge treatment 1Arrows indicate possible flowpaths3

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The common unit operations of sludge treatment and disposal involve concentration orthic"ening, digestion, conditioning, dewatering, oxidation and safe disposal. 6ig.;.%0represents the general flow sheet of sludge treatment techniques in approximately theorder in which they could be applied in a treatment scheme.

Concentration

The purpose of concentration or thic"ening is to remove water from the sludge andreduce its volume as much as possible so that the sludge can be handled more efficiently.The common methods for thic"ening are gravity settling and flotation. In gravitythic"eners the sludge is subEected to gentle agitation by means of a slow stirrer whichenhances settling. In this manner the combined sludge from primary and secondarysettlers can be thic"ened so as to contain !;R solids. $ften the thic"ening of activatedsludge is complicated by anaerobic action, particularly under warm conditions when thebacteria in the sludge decompose organic matter and release gases. This also createssettling and odour problems. The sludge can also be thic"ened by air flotation,

particularly the secondary sludge, which "eeps the system aerobic. The flotationtechnique can concentrate the sludge to bring its solids content to 0R.

Digestion

After concentration, the sludge is stabiliBed by digesting it under aerobic or anaerobicconditions. Anaerobic digestion is the most common method in which the organic contentof the sludge decomposes to give mainly methane and carbon dioxide and at the sametime the bound water is released from the sludge. 7roperly digested sludge is blac" with afaint smell of tar, and is stable. In a typical sludge digester, shown in 6ig. ;.%, rawsludge is fed into the active digestion Bone and gas lifts the sludge particles and othermaterials which form a supernatant layer on the top of the digestion Bone. The gas iscollected at the top and the digested sludge is withdrawn from the bottom. The normaldetention period in standard digesters varies from -+ to + days depending upon thetemperature conditions.Aerobic digestion is also used, and it may be considered similar to extended aeration. Thesludge is aerated in a tan" for about %+ days at ambient temperatures. During the processthe bacterial cells are destroyed and a substantial portion of the sludge is oxidiBedresulting in the reduction of the solid content by about -+R. (ometimes shallow lagoonsare employed as digesters. Harge land areas are required for sludge lagoons and odourproblems may occur frequently.

ConditioningThe sludge after stabiliBation may be conditioned to improve its dewateringcharacteristics. This is done by adding chemicals li"e iron salts, alum, lime andpolyelectrolytes. These chemicals bind the sludge particles together and encourage therelease of absorbed water. 7hysical conditioning methods such as heat treatment arebecoming popular. The sludge is heated under pressure and after a period of time the gelstructure of the sludge brea"s down so that the water is released. :eat treatment has theadvantage of steriliBing the sludge> at the same time the sludge is partially oxidiBed andcompletely stabiliBed.

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DewateringThe thic"ened sludge is dewatered for efficient handling and disposal. Dewatering isaccomplished by mechanical methods, the most common being centrifugation andfiltration, which includes pressure filtration and vacuum filtration. In centrifugation,

conditioned sludge is added to a rotating bowl that separates the sludge into a ca"e and adilute stream. The solid ca"e is transported within the bowl and is removed by a screwconveyor at one end of the bowl> the liquid is removed at the opposite end 16ig. ;.%53.#entrifugation is a compact method which requires careful control of process variables.6iltration, using plate!and!frame pressure filters or rotary drum vacuum filters, is widelyused for dewatering digested sludge. In pressure filtration, the sludge is pumped slowlywith increasing pressure into filter plates supporting a cloth, which retains the solids. It isa batch process, and after the dewatering period the plates are separated and the sludgeca"e removed. 7ressure filtration can produce a ca"e with a solids content of %!+R. Incontrast to pressure filtration, vacuum filtration is a continuous process where a rotatingdrum, which is covered with filter cloth, is partially submerged in the sludge. $n

applying a vacuum of /+!;+ "7a inside the drum, the liquid is suc"ed into the drum. Theca"e is deposited on the outside of the drum and is removed by a scraping mechanism.'acuum filtration yields a dewatered sludge with a solids content of about %R.Drying beds are also commonly used for dewatering. The bed consists of a filteringmedium on which the sludge is applied to a depth of upto %+ mm, depending on thesolids content. Dewatering ta"es place by a combination of drainage and evaporation.Femoval of dried sludge is carried out mechanically. Another technique, heat drying, maybe utiliBed in applications where the sludge is to be incinerated or when a saleablecommodity can be produced. A maEor problem associated with this process is the controlof gases and ash particles which may be generated in drying.

Oxidation&efore the final disposal, some sludges may be oxidiBed to reduce the organic content,with the consequent destruction of bacteria and a significant reduction in their volumes.Incineration and wet oxidation are the two common methods employed for sludgeoxidation. Incineration is usually performed in a multiple hearth furnace, althoughfluidiBed beds or flash dryers may also be used. In the multiple hearth furnace the sludgepasses downward through a series of hearths. 'aporiBation of moisture occurs in theupper hearths, followed by incineration in the lower ones. The combined efficiency ofevaporation and incineration in multiple hearth furnaces is about R. The fluidiBed bedsystem consists of a bed of sand fluidiBed by air. When the sludge is introduced, thesludge particles are dried almost instantly as they are dispersed, and are oxidiBed.Wet oxidation is a process in which the sludge is ground, mixed with air in stoichiometricproportions, and then subEected to high temperatureThe sludge from the digester may contain about ;+ to ;-R water. The sludge is de!watered in drying beds, filter presses or vacuum filters. The de!watered sludge, afterchlorination, can be sent for ultimate disposal. The various methods used for ultimatedisposal include dumping in landfills, incineration, dumping at selected sites in sea, orutiliBing as a low grade fertiliBer.

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ERIAR6 OR A@AN!E WASEWAER REA*EN

Table *.*, indicates, not all of the impurities in a waste water stream are removed byprimary and secondary treatment. $rdinarily, the remaining quantities would be disposedof naturally in the river which received the effluent, but the growth of population andindustry and its concentration along rivers require that most water be used many times

before it reaches the ocean. In many cases the increments of pollution remaining afterordinary treatment are too large for natural removal prior to the next use. Thus, a numberof tertiary or advanced wastewater treatment techniques are becoming important,although at present only a very small percentage of municipal systems use them 1Table*.*3. (everal of these methods are also applicable to industrial wastes where &$D andsuspended solids may not be the most important indicators of water quality, and indeed anumber of them find much greater use in such applications. In addition, they may beemployed at the beginning 1water purification3 as well as the end of the human water usecycle.Activated carbon adsorptionGltrafiltration

SlectrodialysisIon exchangeFemoval of bacteria and virusesFemoval of nitrogen and phosphorusDisposal of treated wastewater in spoilsAgricultural wastes

7. /0, DaraSvaporationIon!exchangeAdsorptionSlectrodialysisSlectrolytic recoveryFeverse osmosis

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5-408 Environmental pollution and Industrial waste management

#$ Deposition of Atmospheric pollutants and their effects. Acid rain, (ome air pollutantscase 1Hondon smog, &hopal disaster, #hernobnyl disaster, etc3. Air quality standards.(ampling and )onitoring.

($ atural water!Sutrophication. :eavy metals and their removal, (ources and effects ofpollution by mercury, lead, Arsenic and chromium. #ase studies!&ioamplification1)inamata disease etc.3.

)$ Industrial monitoring, #oncept of threshold limit value, time weighted average andshort term exposure limits. )ethods of monitoring, exposure, active and passive,diffusive monitors, Draeger tubes, portable2sampling device, Analytical techniques.

4$ Wastewater treatment

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$rigin of wastewater> #haracteriBation of wastewaters> (ampling and methods ofanalysis> )ethods and equipment used in wastewater treatment 7reliminarytreatment> 7rimary treatment> (econdary 1&iological3 treatment, (ludge treatment anddisposal> Advanced or tertiary treatment, Fecovery of materials from processeffluents.

:$ Wastewaterfrom some typical industries 1Wastewater sources, characteristics, effectsand treatment options37ulp and paper, tanneries, fertiliBer, sugar industry, pharmaceuticals, textile, soap anddetergent manufacturing, chloro!al"ali industry, iron and steel manufacturing, thermaland nuclear power plants, photochemical industry.

;$ #urrent industrial environmental status> 8uidelines and discharge standards of variousindustries permit system for discharge2emission. 7rocedures for underta"ing SIA andtheir evaluation.

----------------------------

4$ Wastewater treatment

$rigin of wastewater N-P> #haracteriBation of wastewaters N%P> (ampling and methods

of analysis N-P> )ethods and equipment used in wastewater treatment 7reliminarytreatment> 7rimary treatment 1sedimentation, coagulation, equaliBation,neutraliBation3 N%,*P>. (econdary 1&iological3 treatment 1aerobic aerated lagoons,tric"ling filters, activated sludge process, oxidation ditch process, oxidation pond>anaerobic sludge digestion, sludge treatment and disposal3 N%,*P, (ludge treatmentand disposal N-P> Advanced or tertiary treatment 1evaporation, ion exchange,adsorption, chemical precipitation, electrodialysis, electrolytic recovery, reverseosmosis3 N%,*P, Fecovery of materials from process effluents N-P.

/oo Re'eren&e

*. Snvironmental chemistry and pollution control, (.(. Dara, p. +!/.%. Waste water treatment, ).. Fao and A.9. Datta, 7. *;.-. Snvironmental pollution control engineering, #.(. Fao, p. %/-!%/, -*-!-%.0. Snvironmental #hemistry, 6ifth edition, A.9. De

:$ Wastewater 'rom some t%pi&al industries 1Wastewater sources, characteristics,effects and treatment options3 7ulp and paper, tanneries, fertiliBer, sugar industry,pharmaceuticals, textile, soap and detergent manufacturing, chloro!al"ali industry,iron and steel manufacturing, thermal and nuclear power plants, photochemicalindustry.

1Wastewater sources> characteristics> effects and treatment options3

/oo Re'eren&e

*. Waste water treatment, ).. Fao and A.9. Datta, 7. *;.

;$ #urrent industrial environmental status.8uidelines and discharge standards of variousindustries permit system for discharge2emission. 7rocedures for underta"ing SIA andtheir evaluation.

/oo Re'eren&e

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*. Snvironmental management SIA, (.(. Dara, p. %*)ulti choice questionsTrue2 6alse questions/oo Re'eren&e

*. Snvironmental chemistry, &. 9. (harma, p. water pollution !0*.