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ChemicalEngineeringJournal95(2003)163–169Chemicalcatalyticreactionandbiologicaloxidationfortreatmentofnon-biodegradabletextileeffluentS.M.Ghoreishi∗,R.HaghighiDepartmentofChemicalEngineering,IsfahanUniversityofTechnology,Isfahan84154,IranAbstractTheeffectivenessofacombinedreduction–biologicaltreatmentsystemforthedecolorizationofnon-biodegradabletextiledyeingwastewaterwasinvestigated.Inthistreatmentsystem,abisulfite-catalyzedsodiumborohydridereductionfollowedbyactivatedsludgetechniquewasusedinordertoremovethecoloratambienttemperatureandpressure.Thisexperimentalstudyconsistedoftwomajorparts:reductiontreatmentandbiologicaloxidation.Bothsyntheticandactualwastewaterwasusedinthisresearch.Syntheticwastewaterwasmadebyseveralgroupsofdyessuchasdirect,basicandreactivecolors.ActualwastewaterwascollectedfromtwodifferenttextileindustriesinthecityofIsfahan,Iran.Thecharacterizationofrawandtreatedwastewaterwascarriedoutbyinfraredandultravioletspectrometers.Theresultsofthisstudydemonstratedthatthenewlydevelopedtreatmenttechniquedecreasedcolor,biochemicaloxygendemand(BOD),chemicaloxygendemand(COD)andtotalsuspendedsolids(TSS)by74–88,76–83and92–97%,respectively.TheIRandUVanalysesshowedthatnon-biodegradabledyesareconvertedtobiodegradableorganiccompoundssuchasalkylandalkenes.Anothermajoradvantageofthismethodwithrespecttoothermethods,namely,adsorptionandcoagulation,wasthatitremovescolorwithoutcausinganydisposalproblem.Theoptimumdosagefortreatmentofactualwastewaterwasfoundtobe50–60mg/lforcatalystbisulfiteand200–250mg/lforsodiumborohydride.Finally,abench-scaleexperimentalcomparisonofthistechniquewithotherreportedcombinedchemical–biologicalmethodsshowedhigherefficiencyandlowercostforthenewtechnique.©2003ElsevierScienceB.V.Allrightsreserved.Keywords:Textileeffluent;Dye;Chemicalreduction;Biodegradation;Colorremoval1.IntroductionTheefficientremovalofdyesfromtextileindustryef-fluentsisstillamajorenvironmentalchallenge.Typically,textilewastewatersconsistofavarietyofwastestreamsfromdifferentoperations.Somedyestuffsarehighlystruc-turedpolymersandareverydifficulttodecompose.Cur-rently,variouschemical,physicalandbiologicaltreatmentmethodsareusedtoremovecolor.Becauseofthehighcostanddisposalproblems,manyofthesemethodsfortreatingdyewastewaterhavenotbeenwidelyappliedinthetex-tileindustries.Aliteraturesurveyshowsthatresearchhasbeenandcontinuestobeconductedintheareasofchem-icalandcombinedchemical–biologicaltreatmentsinordertoimprovethebiodegradationofdyestuffsandminimizethesludgeproduction.Previousstudieshaveshownthatmanyofthedyesarecar-cinogenic,mutagenicanddetrimentaltotheenvironment.Astoxicitystandardsbecomemorecommonandstringent,the∗Correspondingauthor.Tel.:+98-311-3915604;fax:+98-311-3912677.E-mailaddress:ghoreshi@cc.iut.ac.ir(S.M.Ghoreishi).developmentofnewtechniquesforminimizingtheconcen-trationofdyesandtheirbreakdownproductsinthewastew-ateralsobecomesnecessary.Protectionofhumanhealthandtheenvironmentisnowperceivedasmoreimportantthantheprofitabilityandefficiencyofabusiness.Thewastewaterdischargedfromadyeingprocessinthetextileindustryex-hibitslowbiochemicaloxygendemand(BOD),highchem-icaloxygendemand(COD)andishighlycolored.Hence,theneedforchemicaltreatmentisnecessaryinordertoproduceamorereadilybiodegradablecompound.Chemicalcolorremovaltechnologieswhicharereportedintheliter-atureincludeadsorptionbyactivatedcarbon,electrochemi-caltreatment,ozonation,chemicalprecipitation,membranefiltration,hydrogenperoxide,Fenton’sreagentandreverseosmosis[1–8].Thehighcostanddisposalproblemshaveopenedthedoorforfurtherinvestigationofnewtechniques.Applicationofconventionalbiologicalprocessesinthetreat-mentoftextilewastewaterhasbeenextensivelyreportedintheliterature[9–13].Theresultsfromaliteraturereviewsupporttheconclu-sionthatwastewaterscontainingwatersolubledyesaregen-erallynotdecolorizedeffectivelybytheaerobicbiologicaltreatment.Shauletal.[14]conductedaliteraturereview1385-8947/$–seefrontmatter©2003ElsevierScienceB.V.Allrightsreserved.doi:10.1016/S1385-8947(03)00100-1164S.M.Ghoreishi,R.Haghighi/ChemicalEngineeringJournal95(2003)163–169thatindicatedadsorptiontothesludgeistheprimaryre-movalmechanismfordyesinabiologicalwastewatertreat-mentsystemandthatfactorsinhibitingpermeationofthedyethroughthemicrobialcellmembranereducetheeffec-tivenessofbiologicaldegradation.Manyinvestigators[1,13,15]haveexaminedawideva-rietyofmaterialslikefly-ash,peat,sawdust,browncoalandbagassepithforcolorremoval.Theinabilityofbiologi-caltreatmentprocessesindegradingdyecompoundsmakeschemicaltreatmentanecessarystagepriortobiotreatmentinordertoproducemorereadilybiodegradablematerials.PaggaandTaeger[16]usedtheactivatedsludgeasbiomassintheadsorptionofdyestuff.Withdifferenttypesofacti-vatedsludgetreatmentmethods,thefollowingremovalsarenormallyachieved:about90%ofBOD5,40–50%ofCODand10–30%ofcolor[9,13,17].Theobjectiveofthisresearchwastoevaluatetheeffec-tivenessofanewcombinedchemicalreductionandbio-logicaloxidationtreatmentsystemforthedecolorizationofnon-biodegradabletextiledyeingwastewater.2.MaterialsandmethodsBo