Control of membrane fouling by Hydrogen Sulfide (H2S) diffusion ...

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have moderate correlation due to lowamount. According to the currentresearches, proteins are the most importantfactor of membrane fouling (Meng et al.,2006).Soluble microbial product (SMP)SMP are the large amount of solubleorganic substances that are produced frombacterial populations in bioreators. SMPlevel is extremely important for biologicaltreatment process as treatment efficiencyand effluent quality highly depends on SMPamount in treatment reactors. It is wellestablished that majority of soluble organicsubstances come from SMP in effluent inbiological treatment systems and itsconcentration set up the discharge level ofchemical oxygen demand (COD) and totalorganic carbon (TOC) in effluent.Furthermore, some SMP have certaincharacteristic like toxicity and metalchelating properties which affect themetabolic activities of microorganisms bothin receiving water and in treatment process.In some case, it lessens the specificrespiration rate of microorganisms.Therefore, for better efficiency of treatmentsystems, less concentration of SMP isdesirable (Liang et al., 2007).SMP could be again categorized into two asutilization associated products and biomassassociated products. Although humicsubstances (humic and fulvic acids),carbohydrates and proteins have beenidentified successfully as major componentsof SMP, it is still unclear of its precisecomposition (Liang et al., 2007).However, most of previous studiesconcentrated on SMP in conventionalbiological treatment plants but fewer havebeen focused to grasp the impact of SMP inMBR. It is found from study that dependingof the operation condition SMP are liablefrom 26 to 52% of membrane fouling inmicrofiltration and ultrafiltrationmembranes (Liang et al., 2007).Materials and MethodHydrogen Sulphide (H 2 S) diffusionAir and mixture of air & H 2 S was sprayedinto sludge for getting differentconcentration of H 2 S in sludge. Pressure andflow rate were 2 bars and 400 ml per minrespectively and was aerated for 15 min andafter then kept it for 10 min forhomogeneous distribution of H 2 S in sludge.High concentration of H 2 S (2000 mg/l) hasbeen diluted by mixing of compressed air toget a certain concentration of H 2 S. Two gasflow meters were used to control the air andH 2 S gas flow and connected to the gascylinder by plastic tube line. This mixture ofgases has been applied to feed by diffuserwhich was connected at the end of sourcetube. Concentration of 25 ppm (0.075 mgH 2 S/g biomass), 50 ppm (0.15 mg H 2 S/gbiomass) and 100 ppm (0.3 mg H 2 S/gbiomass) of H 2 S were sprayed in threesamples with flow rate of 400 ml/min andeach sample is amount of 2 liters. Only airwas pumped into the sludge to get zeroconcentration H 2 S sample for same durationwith flow rate 400 ml/l. These samples wereanalyzed for eEPS, SMP, ZP and pH.H2S TankAir TankRegulatorRegulatorH2SFlowmeterAirFlowmeter2 mtubeline2 L Glass CylinderFigure 1: Schematic setup for H 2 S diffusionDead End FiltrationThe whole experiment was consisted ofdead end filtration cell, reservoir,compressed air and computer program formeasuring weight of collected permeate.Around one liter of aerated sludge is pouredin about 2 l volume closed feed reservoirand pump to dead end filtration cell (110 mlvolume capacity, 1.59 X 10 -3 m 2 membrane2
area). PVDF membrane (0.189 cm 2 ) withpore size of 0.22 µm is placed at on porousmedia at the end of cell and rubber circularring is placed on the membrane to preventleakage. Dead end cell is completely airtight and connected to feed tank by rubbertube. Compressed air cylinder is connectedto the tank through pressure gauge andpressure stabilizer for pumping sludge fromtank to cell. Applied air pressure iscontrolled by EL PRESS P-702CM pressuretransducer installed in the line tubing, whichis then connected to an EL PRESSelectronic regulator for a more accuratecontrol of pressure. Filtrated supernatantweight is measured every 60s by computerlinked balance and computer programcalculate the flux rate.Air tankAutomatic pressureregulatorPressure ControllerReservoirDead-endfiltration cellMass balanceFig 2: Dead-end filtration set-upPermeat eComputerSource of biomassBiomass has been collected from NorthHead MBR and Malabar MBR which wasoriginally from North Head’s MBR. Bothsewages go to MBR after primary treatmentand are a mixture of municipal andindustrial waste. Sludge age of Malabar is20 days and about 13L of sludge is wastedeach day to keep the sludge age at 20 daysand hydraulic retention time (HRT) is about10 hours. Volume of MBR is 250 l and thetotal membrane area is 2 m 2 with constantflux at 12 l/h.Nine samples have been used for theexperiment marked from A to I. Sampleshave been randomly selected for differenttests and observed the effect of H 2 S on thisparticular sludge characteristic.3SMP and EPS extractionHeating method has been followed toextract SMP and EPS. Sample is centrifugedfirst at 2000 rpm and supernatant is filtratedthrough 1.2 µm pore size filter paper forSMP extraction. The suspension was dilutedwith 0.98% NaCl solution, mixed for 5 minand kept it 80 0 C temperature for 10 min.This temperature has been controlled byhigh pressure stream sterilizer (ES-315).After then it was centrifuged at 2500 rpmand supernatant was again filtrated using 1.2µm pore size filter and collected for EPSextraction.Carbohydrate analysisPhono-Sulfuric acid method proposed byHanson and Philips, 1981 was used todetermine the carbohydrate concentration ofSMP and extracted EPS. In presence ofsulfuric acid, phenol and carbohydrate formcolored aromatic compounds and measuredit as an absorbance at 480 nm wave lengthby spectrophotometer. Concentration ofcarbohydrate then was determined from thevalue of absorbance using carbohydratecalibration curve which was developed fromstandard solution.Concentration, mg/lCarbohydrate Calibration353025y = 93.487xR 2 = 0.9891201510500 0.05 0.1 0.15 0.2 0.25 0.3 0.35Absorbance at 480 nmFig 3: Carbohydrate calibr. curve at 480 nmProtein analysisModified Lowry method has been used tomeasure the concentration of protein ofSMP and extracted EPS from filtrate whichwas modified by Peterson (Peterson, 1977).In this method, bonded proteins react tolowry reagent which contains copper ionsand Folic-Ciocalteu reagent composed ofphosphomolybdate and phosphotungstate.When lowey reagent is added to the filtrate,copper ions together with protein form a
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