IntroductionTextile production involves number of wet process like, finishing,drying ,dyeing, printing, bleaching, washing, desizing etc. Eachprocess generates wastewater containing different type of pollutantslike dyes sizing agents, salts and dyeing auxiliaries . For fixing of dyesdifferent types of salt are used like sodium chloride,sodiumsulphate,sodium nitrate and sodium carbonate etc.scouring anddesizing process.azo dyes are mostly used in dyeing process.azodyes cause coloured wastewater.azo dyes have electron withdrawingcapacity due to n=n bond.in conventional treatment it is difficult todecolourise the textile wastewater.for treatment of textile wastewater various physicochemicals(like coagulation,membranefiltrationand adsorption)advanced oxidation process(fenton ultraviolet and h2o2 oxidation) biological processes(conventional activatesludge and extended qeration activated sludge)A combination of these processes can also be applied for treatmentof textile wastewater.2 synthetic waste water composition:-The composition of synthetic wastewater is as follows[muda etal.2010]:-Nh4cl 0.16 g/l ,kh2po4 0.23 g/l k2hpo4 0.58 g/l,Cacl2.2h2o .07 g/l,mgso4.7h2o 0.09 g/l, edta 0.02 g/l and tracesolution 1 ml/l.The carbon sources used were glucose 0.5 g/l.
The composition of trace elements was h3bo3 0.15g/l ,fecl3 1.5g/l,zncl2 0.12 g/l mncl2.4h2o 0.12 g/l fecl3.4h2o 1.5 g/l zncl2 0.12 g/lnamoo4.2h2o 0.06 g/l,cocl2.6h2o 0.15 g/lAnd ki 0.03 g/l . The ph of synthetic wastewater was approximate to73 sludgeIt is residual material left from industrial waste water or sewagewaste water processes. It consists of micro-organisms,non-livingorganic matter & inorganic materials.Physical properties of sludge3.1.1 sizeThe avg. Dia of microbial granular slude is 2.3+_1.0mm according tomuda et al 2010.according to peng et al 1999,the diameter ofdeveloped aerobic granules is in the range of 0.3-0.5 mm which issmaller as compared to aneorbic granules that can be upto 2 to 3mm.3.1.2Settling velocityFor seed sludge the avg. Settling velocity was 9.9+_0.7M/lAnd for seed anerobic granular sludge it was 42+_8 m/h
[muda et al 2010]. The avg settling velocity of the anerobic granularseed is in range of 18-100m/h by schmit and ahring 1996.at the endof experiment avg settling velocity for granular sludge was increasedfrom 17.8+_2.6 m/h to 80+_8m/h.Developed microbial granular sludge possesesHigh settling velocity.This enabled the granules to escape from being flushed out.generallyas the no. Of operational days increases the bio mass concentrationand settling velocity also incresses.3.1.3 granular strengthThe granular strength of the granules was measured based onintegrity coefficient [ghangrekar et al 2005].if ic value is small ,thenstrength will be higher.generally as the operation days increases as icvalue decreases. According to ghangrekar et al 2005 granules whichhave ic value less than ware considered high strength granules.The microbes in the granules were loosely linkes at the early stage ofgranular development.as more microbes were linked together , thegranules increased in size. So the microbes produces more eps thatcauses the granules to become denser and stronger.3.1.4. Mineral contentThere are some mineral present in sludge like na+ k + ca2+ mg2+ etcMechanism of colour removalYhe mechanisim of colour removal is adsorption of the dye onto thebiomass (brass et al 2001).In during adsorption ,the dye is concentrated onto biomass.
Bio association b/w the dye and the bacterial cells tends to thebiological reduction of azo dyes .most of the azo dyes havesulphonates substituents groups and a high molecular weight.1 there are two mechanism for the decoloration of azo dyes asterminal electron during bacterial catabolism connected to atpgeneration2 a gratuitons reduction of azo dyes by the end products of bacterialcatabolism not linked to atp generation.Factors affecting colour removalThe composition of textile waste water include organics, nutrients,salts, sulphur compound , toxicants and colour .Any of these compounds may create inhibition to dye reductionprocess.1 oxygenThis is the most important factor to consider in color removalprocess .it is the effect of oxygen on cell growth and dye reduction.inaerobic condition during the reduction stage oxygen may inhibit thedye reduction mechanism .because the electron doners by the cellsis used to reduce oxygen rather than the azo dye.for efficient colourremoval should be avoided[chang et al 2000]in aerobic conditionafter reduction of azo bond there is no further reduction of yhe dyemolecule.2temperature
In many system the rate of color removal increase with withincreasing temperature. The temperature required to produce themax rate of colour removal tends to optimum cell culture growthtemperature of 35-45 c3 phThe optimum ph for colour removal is approximately 7 or slightlyalkaline value .the reduction of azo bond can increase the ph valuedue to formation of the aromatic amines.4 dye concentrationThe concentration of dye can affect the efficiency of colour removal4dye structureDyes those have simple structure and low molecular weight.theyexihibit higher rates of color removal but for highly substituted andhigh molecular weight dyes , color removal is difficult.In dyes when electron withdrawing group like –so3h -s02nh2 are inthe para position of the phenyl ring , relative to the azo bond theircauses an increase in the reaction rate.Colour removal also depends on the no if azo bonds in the dyemolecule .the colour of the monoazo dye is removed faster than isthe colour of diazo or triazo dye according to hiltz et alA acid dyes exihibit low colour removal due to a no of sulphonategroup in the dye
B direct dye exihibit high level of colour removalC reactive dye eihibit low levels of colour removalElectron donorAccording to bras et al ,the addition of electron donor such asglucose or acetate ions increases the reduction cleavage of azo bond.Coenzyme reducing equivalents act as the electron donors for azodye reductionRedox potential as rate determining step involves a redoxequilibrium b/w/ the dye and reducing agent.so colour removaldepends on the redox poentialof the electron donor and electronacceptors.if the redox potential of the system is at most negativethen colour removal rate will be highest.if we increases redoxpotential of the system , the colour removal rate decreases.Technologies available for colour removalThere are two possible location :-1 at the dye house ,to remove colour2 at the sewage works to treat colourMethods of treatment of waste water
1 physical/chemical methods Oxidation Adsorption Membrane technologies Coagulation/flocculation2 Conventional active sludge Entended aeration activated sludgeOxidationOxidative process representes a widely used chemical method forthe treatment of textile wastewater treatment.the main oxidizingagent is h2o2.hydrogen peroxide is added to an cidic solution (ph =2-3) containing fe2+ ions.it is called fenton reaction .it mainly used inpre-treatment. The reaction is exothermic and it takes place at hightemperature.the great amount of total cod removes to fe(oh)3 co-precipitation .the main drawback of this method are the significantaddition of acid and alkali to reach required ph , to high discharge infinal effuluent.The ozone oxidation is also a very effective decolourising processozone can easily vreak the double bond of the dyes. It can oxidize asignificant portion of cod.The –ve effect carcinogenic aromatic amines, i.e toxic.Adsorption
In this process the mixing of waste water and the porous materialpowder orgranules occurs.in this method ,the pollutants in the wastewater are removed on the surface of the porous material of filtercommonly used adsorbents are activated carbon ,silicon polymers ndkaolinMembrane separation processIn this method the membrane’s micropores are used to filter and toseparate certain substance in wastewater .this method is based onmembrane pressure some of the methods are reverse osmosisultrafiltration ,nano filtration and microfiltration.Coagulaton flocculation sedimentationColloidal type of very small type material have electrical changes.these changes give repulsion and prevent their aggeration by addingwater electrolytic products,ployelectrolyte can eliminate the surfacecharges of the colloids .this effect is known as coagulation.Biologica wastewater treatmentAccording to different oxygen demand biological treatment methodscan be divided into aerobic and anaerobic treatment.Aerobic biological treatmentAccording to the oxygen demand of different bacteria , the bacteriacan be divided into aerobic bacteria . Anaerobic bacteria andfacultative bacteraia.
Aerobic biological treatment can be divided into major categoried :-activated sludge process-Activate sludge is a kind of floc which is mainly comprised of manymicroorganisms and has strong ddecomposition .in present theoxidation ditch and sbr process are commonly used activated sludgeprocessOxidation ditchThe oxidation ditch is generally consisted of the ditch body of ringshape. Wastewater activated sludge and various micro organisms aremixed in a loop ditch oxidation ditch has a long hrt; low organicloading and long sludge age . It has high purification stable reliable,simple,easy,low investment and energy consumption.Sequencing batch reactor activated sludge processIts operation is mainly composed of five processes-1 inflow2 reaction3 sedimentaton4 outflow5 standby.Sbr process have high removal rate of cod as well as high removalefficiency of colour.
Anaerobic biological treatmentIn this method the anaerobic bacteria used. This is a good methodfor treatment of waste water .the uasb reactor is used for treatmentof simulated textile wastewater.As azo dyes have n=n bond in structure ,thereore theirbiodegradation are impossible under aerobic condition .in aerobiccondition oxygen are used as electron acceptor instead of azo dye .In anaerobic condition azo dye are used as electron acceptor ,sobreakdown of n=n bond occurs .thus decolouration is possible.ConclusionThe salt concentration of 32g/l was optimum for 82.5% removal ofcod at a hrt of 20 h . At 128 g/l cod removal efficiency decreased to18.5% in vasb reaction generally as nacl concentratioion of usabreaction increases cod removal efficiency decreases [isik,2004],stateoperation is possible with salt concentration up to 27-30g nacl .clolurremoval efficiencies were not affected with ncreasing saltconcentration in usabreactor.After the ssalt concentration of 32g/l , the methanogenic bacteriacould be inhibited. The high salt concentration reduces methanepercentage. it si possible to obtain high decolouration yields ofazo dyes in methanogenic usab reactor (bras et al 2005).higherdecolouration yield is obtained for diazo than monoazo (bras et al2005).
Combines anaerobic – arobic usab reation a method for completeremoval of azo dyes from wastewater.at higher hydraulic retentiontime. The colour removal efficiency can be used in both aerobic &anaerobic.