Treatmentofsewagewaterfromtouristareasbyanaerobic®xed-bedreactor
Ânchez,R.Borja,*O.Reyes,M.CruzandM.F.ColmenarejoE.Sa
Alaboratory-scaleanaerobic®xed-bedreactor,operatingatambienttemperature(30to35°C),wasusedtotreatsewagewaterfromtouristareasinCubaathydraulicretentiontimes(HRT)rangingfrom4to72h.Thetotalchemicaloxygendemand(T-COD),totalbiologicaloxygendemand(T-BOD)andtotalsuspendedsolidsremovalvariedbetween30and80%,40and95%and25and80%,respectively.Totalandfaecalcoliformswerereducedby98.1to99.9%andby99.0%to99.9%respectively,despitethemarkeddecreaseinHRTfrom72to4h.Keywords:Anaerobic®xed-bedreactor,coliforms,sewagewater,touristareas.
Anaerobic®xed-bedreactorswereintroducedforsewagewatertreatmentatanoxicconditionswithgreatsuccessbyCoulteretal.(1957).Inthesereactorsthesupportfunctionsintheattachingandimmobilizingofthemi-croorganismsinanactivebio®lm.Thereactorischar-acterizedbyahighcapacityoforganicmatterremovalatlowvaluesofhydraulicretentiontime(HRT).Thepro-cessistechnicallysimpleandeasytooperate.DifferentauthorshavestudiedtheeffectofHRTonthebiologicaloxygendemand(BOD)removal,obtainingef®cienciesintherangeof43to87%atHRTsof8to36h(Genungetal.1979;Kobayashietal.1983;Wheatley,1983;Yamamoto1983;Genungetal.1985;Inamoryetal.1986).Domesticwastewateroriginatingfromsmallfarmsandprivatehouseshasbeentreatedbyacombinationofsedi-mentationfollowedbyanoxicpeatbio®lterwithoverallBODremovalef®ciencyof80%andchemicaloxygendemand(COD)removalof74%athydraulicloadingsof14to27l/m2.hbyWierzbickietal.(1992).Angladaetal.(1989)studiedtheapplicationofadown-¯ow®xed-bedreactortosewagetreatmentatlaboratoryscale.Ef®ciencyinCODremovalrangedfrom61to80%asafunctionoftheorganicloadingrate(OLR)applied,whichrangedfrom1.2to0.55gCOD/l.d,respectively.VandenBerg
etal.(1981)studiedthetreatmentofsewagesludge(55gCOD/l)andliquorfromheattreatedsewagedigestedsludge(10.5gCOD/l)atanOLRof13.8gCOD/l.din®xed-®lmreactorsoperatingataHRTof4dand9hrespectivelywithCODremovalsofabout70%.Wang(1994)summarizeddifferentalternativesofanaerobictreatmentofsewageincluding®xed-,expanded-and¯uidized-bedreactors,andconcludedthattheanaerobic®xed-bedreactor(AFBR)isanattractivesystemforsmallscaleanaerobicapplications,particularlyforonsitedomestictreatment.
Wehavethereforecarriedoutastudyonanaerobictreatmentofsewagewateroriginatedintouristareasbyusingalaboratory-scaleAFBRemphasizingtheremovaloftotalandfaecalcoliformswiththetargetofwastewaterreuse.
MaterialsandMethods
WastewaterCharacteristics
Wastewatersampleswerecollectedfromahotelnearthelaboratory(Havanacity).Theaveragevolumeofwastewateroriginatingfromtherooms,maintenanceareas,restaurants,cafeteriasandlaundryserviceswasestimatedat250m3/d.Thesampleswereanalysedweeklyover1yearfortotalandsolublechemicaloxygendemand(T-CODandS-COD),totalandsolublebiologicaloxygendemand(T-BODandS-BOD),totalsolids(TS),totalsuspendedsolids(TSS),organicnitrogen(ON),ammonianitrogen(AN),totalphosphorus(TP),orthophosphate(OP),to-talvolatilefattyacids(TVFA),alkalinityandpH(APHA1989).
Ânchez,O.ReyesandM.CruzarewiththeDepartamentodeEstudiosE.Sa
ÂnAmbiental(DECA-CNIC).POBox6990,LaHabana,sobreContaminacio
ÂaCuba.R.BorjaiswiththeInstitutodelaGrasa(CSIC).Avda.PadreGarcõ
Tejero,4.E-41012Sevilla,Spain;fax:34-54-616790.M.F.ColmenarejoiswiththeCentrodeCienciasMedioambientales(CSIC).Serrano115duplicado.28006-Madrid,Spain.*Correspondingauthor.
ã1997RapidSciencePublishers
WorldJournalofMicrobiology&Biotechnology,Vol13,1997
315
E.Sa
Ânchezetal.Table1.Characteristicsofrawwastewater.*
Parameter
MeanvalueStandarddeviationTotalSolublechemical913Totalchemicaloxygenoxygendemanddemand(mg/l)(mg/l)44193Solublebiological2205643Totalbiologicaloxygenoxygendemand(mg/l)Totalsolidsdemand(mg/l)92790Organicsuspended(mg/l)
solids25411427Ammonianitrogen(mg/l)(mg/l)2258Totalnitrogen(mg/l)256Organicphosphorus1956Totalvolatilephosphorus
(mg/l)fattyacids76518684AlkalinityasaceticpH
(mg/l,acid)
(mg/l,asCaCO3)33643TotalFaecalcoliformscoliforms(NMP/100(NMP/100ml)ml)1.77.8´1089.9´1060.10.20.2´´108106*Meanvaluesof48samples.
TotaltechniqueandfaecalcoliformsweredeterminedbytheDurhantubewastewaterThechemical(APHA1989).
issummarizedandmicrobiologicalinTable1.
compositionoftherawExperimentalTheternalAFBRDesign
286diameterpiecesdiametermodelofceramicandconsisted1ringmheight.ofa2-lglasscolumnof50mmin-15.5mmTheincolumnlength,was14.6packedwiththespeci®csupportand6.6mminternaldiameter.Thetotalsurfacemmexternalareaof0.7andsurfacewasarea1146cm2,thetotalvolumewas0.6l,andthetapThecolumnthefreewasvolumewas1.91cm2/cm3.Thebedporositywashermeticallyofthereactorclosed1.4atl.
thetopwitharubberforover¯owthewithbiogastwoconnections,insidethroughoutlet.oneforthein¯uentfeeding,theotherasyphonTheef¯uenttoguaranteeoftheprocessastablewascollectedbyreactorthederBiogaswasreactor,wasfedwhichoperatedinadown-¯owlevelmode.ofliquidThecollectedcontinuouslybymeansbymeansofaplasticofaperistalticgraduatedpump.
chloride¯oatinginwaterinaatglass10%.
cylinderwithasolutionofsodiumcylin-ExperimentalThewithAFBRwasProcedure
inoculatedwith1lofdigestedsewagesludgevolatileatotalwassolidssolids(VS)(TS)wasconcentration66%onadryofbasis5%.whileTheconcentrationthesludgeageoftheOnce40d.
thereactorwasinoculated,tapumesoperationalstateoffreshwastewaterreactorvolumecontinuedwascompleted.waterwastobeaddedIncreasingaddeduntiluntilasteadyvol-startedAfterwasobtained.
theacclimatizationperiod,the4ataHRTof72handcontinuedatHRTexperimentsof53,19,werematelyh,respectively.of1monthEachexperimenthadadurationof12,approxi-8andnewtheviationsexperimentHRTwasconsideredatsteadystate,withadifferentasatransientandaboutthreetimesthevalueHRT.periodOncethebeforestandardstartingde-aminimumofthevalueoperational(lessthanparameters10%inallofcases),theprocessthenextachievedrunwas
the316
WorldJournalofMicrobiology&Biotechnology,Vol13,1997
initiated.followingEf¯uentCOD,ity,T-BOD,operationalsamplesS-BOD,TS,parametersweretakenthreetimesperweek.TheTSS,ON,wereAN,TP,analysed:OP,T-COD,S-ductionpH,totalandfaecalcoliforms(APHA1989).TVFA,Biogasalkalin-pro-was(modeldeterminedwasmeasuredthreetimeseveryadayweekwhileusingmethaneconcentrationstandardMaihakFinor).Thebiogasvolumeanwasinfraredcorrecteddetectortoperimentstemperaturewereperformedandatpressureambient(STP)temperatureconditions.(30toThe35°ex-C).
ResultsandDiscussion
Table2showsthevaluesofthemonitoringparametersoftheprocessstability(TVFA,alkalinityandpH)fortheef¯uentsobtainedatdifferentHRTstudiedoncesteadystatewasachieved.AslightvariationofthemonitoringparameterswasobservedforthedifferentHRTstudied.Signi®cantdifferencescouldnotbeestablished,showingthatprocessstabilitywasnotaffectedforthedrasticre-ductionoftheHRT.Theaveragevaluesofef¯uentTVFA,alkalinityandpHwere661(136,standardde-viationthroughoutthepaper)mg/l,283(36)mg/land8.01(0.11),respectively.Comparingthesevalueswiththoseforthein¯uent(Table1),TVFAandalkalinitydecreasedandpHincreasedwithinacceptablelimitsfortheanaerobicprocess.
Figure1showstheeffectofHRTontheT-COD,S-COD,T-BOD,S-BOD,TSandTSSremovalef®ciencies.Theef®ciencyvaluesdecreasedslightlyintherange72to19handmarkedlyforlowervaluesofHRT.T-BODre-movalef®ciencyrangedbetween95and79%atHRTbetween72and12hrespectivelyandwashigherthantheef®ciencyvaluesoftherestofthemeasuredpara-metersduringtheexperiment.Removalofsolubleor-ganicmatter(S-CODandS-BOD)waslowerthanthesuspendedorganicmatterremoval,whichwascoin-cidentwiththeresultsreportedbyotherauthors(De-walleetal.1981;Kobayashietal.1983;Switzenbaum1983)whoconcludedthatthissystemisveryeffectiveintheremovalofsuspendedorganicmatter.
Table2.Monitoringparametersoftheprocessstability.*
Run
HydraulicretentionTotalAlkalinitytime(h)
fattyvolatile(acid((mg/l)SD)(mg/l)SD)(pHSD)
12725363119431(37)(30)267(17)8.06312740(59)341(29)8.05(0.09)(0.12)48884(70)2508.04(0.16)54
627658
(59)318(24)8.12(0.09)6(68)
238(30)286
(22)(28)
7.987.79(0.13)(0.19)
*Meanvaluesof15samples.(SD),standarddeviations.
Figure2showstheeffectoforganicloadingrate(OLR)ontheT-BODremovalef®ciencyandmethanegasyield(expressedinlitres/gCODadded).T-BODremovalef®cienciesintherangeof79to95%wereobtainedatOLRbelow1.26gCOD/l.d.WhentheOLRincreasedoverthisvalue,removalef®ciencydecreasedrapidlyachievingaminimumvalueof49%at3.70gCOD/l.d.MethaneyielddecreasedslightlyatOLRsbetween0.21and0.79gCOD/l.dandincreasedathighervaluesofOLR.
TheresultsoftheeffectofHRTontotalandfaecalcoliformsremovalef®cienciesarepresentedinFigure3.Valuesoftotalandfaecalcoliformsremovalwerecloseto100%intheHRTrange72to19h.AtlowervaluesofHRT,totalcoliformremovaldecreasedslightlyto98±99%,whiletheremovaloffaecalcoliformsrangedfrom99%to99.8%.Thehighremovalofcoliformscouldbeattributedtothementionedmechanismsofadsorption
Sewagetreatmentbyanaerobic®lter
,faecalcoliformremovalef®ciencies(%).
and®ltrationoftheprocess.Bio®lmhasalsoagreatca-pacityforsuspendedsolidimmobilizationbytheabove-mentionedmechanisms(RittmannandMcCarty1980;Donovan1981;KennedyandVandenBerg1981;Ritt-mann1982;Johnsonetal.1994).
Acknowledgements
TheauthorswishtoacknowledgethesupportoftheAlexanderVonHumboldtFoundationandProgramofScienti®cCooperationwithIberoamerica(SpanishFor-eignMinistry)indevelopingthiswork.
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