Optimizing the in-line ozone injection and delivery strategy in a multistage pilot-scale greywater treatment system: System validation and cost-bene fi t analysis
K.S. Oh
a, P.E. Poh
a,b,*, M.N. Chong
a,b, D. Gouwanda
c, W.H. Lam
a, C.Y. Chee
daChemicalEngineeringDiscipline,SchoolofEngineering,MonashUniversityMalaysia,JalanLagoonSelatan,BandarSunway,Selangor47500,Malaysia
bSustainableWaterAlliance,AdvancedEngineeringPlatform,MonashUniversityMalaysia,JalanLagoonSelatan,BandarSunway,Selangor47500,Malaysia
cMechanicalEngineeringDiscipline,SchoolofEngineering,MonashUniversityMalaysia,JalanLagoonSelatan,BandarSunway,Selangor47500,Malaysia
dBacteriaFreeWaterEngineering(M)Sdn.Bhd.,7JalanSS13/3,F,SubangJayaIndustrialEstate,SubangJaya,Selangor47500,Malaysia
ARTICLE INFO Articlehistory:
Received13March2015 Accepted28April2015 Availableonline2May2015 Keywords:
Greywater Pilot-scale Filtration Ozone Disinfection
Treatmentperformance
ABSTRACT
Greywaterisapotentialsourceofrecycledwaterforhouseholdthathasoftenbeenoverlooked.Although greywaterislightlycontaminated,aholistictreatmentanddisinfectionsystemofgreywaterisstill warrantedtoensurepublichealthissuesassociatedwiththecross-connectionofthirdpipereticulation inhouseholdareminimized.Thisstudyassessedonthetreatmentperformanceofacommercialpilot- scalegreywatertreatmentsystemcomprisingofamulti-mediumsandfilter,granulatedactivatedcarbon (GAC)filterandanozonationdisinfectionsystem.Theoperationalvolumeflowrate(10–20L/min)and ozonedosingrate(5–20g/h)formaximumremovalofcontaminantsingreywaterwereinvestigated.This studyfoundthattheincreaseinoperationalvolumeflowratedecreasedtheoverallperformanceofthe greywatertreatmentanddisinfectionsystem.Theoptimumoperatingvolumeflowratewasfoundtobe 10L/min,removing72.6%ofchemicaloxygendemand(COD)and42.9%(0.85-logremoval)ofEscherichia coli withoutrecirculation. Recirculationofgreywater wasintroducedto theozonationdisinfection systeminordertoimprovethedisinfectionefficiency.Itwasfoundthatallbacteriapresentinthetreated greywatereffluentwerecompletelydisinfectedwitharecirculationperiodof1h.
ã2015ElsevierLtd.Allrightsreserved.
Introduction
Greywaterisasourceofwastewatergeneratedfromshowers, handwashbasin,laundryorpreparationoffoodinthekitchen[1].
Itisconsistentlygenerateddailyandcontainslowconcentrations oforganiccompoundsandpathogenswhencomparedtodomestic wastewaterwithsewageinputs.Therefore,greywaterhasahuge potentialtobetreated,recycledandreused,especiallywhenthe availability of freshwater is a concern in many arid countries.
Treatedgreywatereffluentcanbereusedforirrigation,carwashing
andtoiletflushingtoaugmenttheavailabilityofdrinkingwaterfor otherpotablefit-for-purposeapplications.
Thoughgreywaterislightlycontaminated,thereisstillaneed fortreatmentbeforereuseasthemicroorganismcontentinthe treatedgreywatereffluentcouldpotentiallycause publichealth issuesthroughclosehumancontact[2].Greywatereffluentthatis deemedsafeforreusecannormallybeobtainedthroughseveral treatment barriers, which include: (i) pre-treatment for the removalofcoarsematerials;(ii)primaryandsecondarytreatments to remove majority of the contaminants and (iii) tertiary disinfectiontreatmenttoensuretheeffluentismicrobiologically safeforhandling.
Todate,differentprocesseshavebeenusedforthetreatment anddisinfectionofgreywatereffluent.Somepopularexamplesof theprimarygreywatertreatmentsystemsarechemicalprocesses, biologicalprocessesandphysicalandphysicochemicalprocesses [3–6]. In general, these systems are operated to reduce solids,
*Correspondingauthorat:ChemicalEngineeringDiscipline,SchoolofEngineer- ing,MonashUniversityMalaysia,JalanLagoonSelatan,BandarSunway,Selangor 47500,Malaysia.Tel.:+60355146272;fax:+60355146207.
E-mailaddress:[email protected](P.E.Poh).
http://dx.doi.org/10.1016/j.jece.2015.04.022 2213-3437/ã2015ElsevierLtd.Allrightsreserved.
ContentslistsavailableatScienceDirect
Journal of Environmental Chemical Engineering
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j ec e
organicandinorganiccontaminantsingreywatersource.Onthe other hand, chlorination, ultraviolet (UV), hydrogen peroxide, ozonation, advanced oxidation are the typical disinfection methods used for greywater [7,8] to ensure that the treated effluentismicrobiologicallysafeforreuse.
Mostpreviousstudiesonthetreatmentofgreywaterforreuse purposewerecarriedoutinlaboratory-scalesystems,mainlyfor understandingtheprinciplesofthetreatmentsystemsaswellasto evaluatetheeffectivenessofindividualunitsofprimary,secondary ortertiarydisinfectiontreatmentsystems[9–13].Todate,thereare limited references available in the open literatures on the treatmentofgreywaterinpilot-orlarge-scalecommercialsystems thatencompassdifferentstagesoftreatment.Thus,itisnecessary toevaluatethemulti-stagetreatmentanddisinfectionsystemasa whole in a pilot- or large-scale commercial system. This is to enabletheidentificationoftreatmentlimitationofacompleteand integrated greywatertreatment system and assess the suitable operatingconditions,providinginsighttourbandevelopersonthe adequacyofsuchsystemforimplementationinnewgreenfieldor retrofittedbrownfielddevelopments.
Thus,themainaimofthisstudywastoassessthetreatment performance of a commercial pilot-scale greywater treatment system comprising of a multi-medium (sand) filter, activated carbon filterand an ozone disinfection system. Conventionally, ozonedisinfectionisconductedfortreatedeffluentretainedina tank,whereozoneisincontactwiththeeffluentforafixedperiod of time. This study examined the use of an in-line ozone disinfectionsystemtoeliminatetherequirementofanadditional disinfectiontank,thusreducingthephysicalfootprintandoverall costofthepilot-scalesystem.Thisstudyalsoevaluatedthecost-
benefitanalysisofhavinganinstalledgreywatertreatmentsystem for recycling purposeagainst thetypical Malaysianhouseholds withonlytheconventionaldual-reticulationwatersystem.
Materialsandmethods Greywater
Bathwaterfromagroupofworkersinafactorylocatedinthe coordinate(3.0692105,101.5965965)wascollectedinapolyvinyl chloride (PVC) tank and transported to Monash University Malaysia fortreatmentonaweeklybasis.Thecharacteristicsof thecollectedgreywaterareaslistedinTable1.
Pilot-scalegreywatertreatmentsystem
Fig. 1 shows the schematic of the pilot-scale greywater treatment system that was used in this study. The pilot-scale systemhasa1.3m3PVCfeedwatertank,whichisconnectedtoa multi-mediumfilterwithastainlesssteelhousinganddimension of 19.05145cm (DH) (ER-19M, BACFREE), followed by a granular activated carbon (GAC) filter (BACFREE), which has similarcapacityastheER-19Mandanozonegenerator(CTO-20, Corona Discharge Ozone Generator). The treated greywater effluentafterdisinfectionwasstoredinanother1.3m3PVCwater holdingtank(cleanwatertank).
This pilot-scale greywater treatment system was also fitted withtwocentrifugalpumpstofacilitatethetransferofgreywater sourcetothetreatmentsystem,aswellasfortherecirculationof treatedgreywatereffluenttotheozoneinjector.Thesystemwas also fitted with several sampling valves along the treatment processtoallowsamplingoftreatedgreywatereffluentatdifferent stagesofthegreywatertreatmentsystem.
Evaluatingtheperformanceofpilotgreywatertreatmentsystem
The pilot-scalegreywatertreatmentsystemwas operated in twodifferentconditionsinordertoevaluatetheperformanceof thesystemandtodeterminetheoptimumoperatingcondition:(i) withoutrecirculationoftreatedgreywater;(ii)withrecirculation oftreatedgreywater.Inthefirstcondition,disinfectedgreywater effluent was directly stored in the clean water holding tank Table1
Greywatercharacteristicforthisstudy.
Parameters Concentration(mg/L)a
pH 6.20–7.66
Turbidity 6.2–48.4
Totalsuspendedsolids(TSS) 42.6–63.3
Chemicaloxygendemand(COD) 63.5–153.0
Biochemicaloxygendemand(BOD5) 45.6–58.5
Escherichiacoli(E.coli) 0–17,900cfu/mL
Pathogenicbacteria 0–3400cfu/mL
Othercoliforms 0–2650cfu/mL
aAllunitsareinmg/LunlessspecifiedandpHwhichhasnounits.
Fig.1.Schematicdiagramofthepilot-scalegreywatertreatmentsystem;(a)greywaterfeedtank;(b)multi-mediumsandfiltrationunit;(c)GACcolumn;(d)ozonation disinfection;(e)recirculationloopwithozonation.
withoutfurtherrecirculation.Theoperatingvolumeflowrateof thegreywaterfedintothepilot-scalesystemwasvariedfrom10– 20L/min toobtaina feedflowrate thatproduces theoptimum treated greywater effluent quality from the treatment process.
Hydraulicretentiontime(HRT)ofeachtreatmentunitislistedin Table2.
Inthesecondcondition,thetreatedgreywatereffluentstoredin the clean water holding tank was continuously recirculated throughtheozoneinjectorforafixedperiodoftime(1–2h).An oxidation–reduction potential (ORP) sensor was installed to monitorthetreatedgreywatereffluentqualityinthecleanwater holdingtank.Whenthegreywatertreatmentsystemwasoperated under low dosage of ozone, bacteria present in the treated greywatereffluentcannotbecompletelydisinfected.Furthermore, thecontacttimebetweenthetreatedgreywatereffluentandozone wasveryshort.Undersuchcondition,recirculationofthetreated greywater effluent for additional contact with ozone could improvethedisinfectionefficiency.Duetothefactthatozoneis ahighlyoxidativegasthat hasharmfuleffects topublichealth whenexposedtotheenvironment,theozonedisinfectionsystem shouldbeoperatedunderthelowestpossibledosage(<20g/h) [14,15].Therefore,recirculationoftreatedgreywatereffluentisa technicallyfeasibleoptionthatisbeinginvestigatedinthisstudy.
The experimental runsconducted in this studyare listedin Table3.Therawgreywaterandtreatedgreywatereffluentsamples weretestedforpH,COD,BOD5,TSSandturbidityinaccordanceto theAmericanPublicHealthAssociation(APHA)StandardMethods (Eaton et al., 2005). Each greywater quality parameter was analysedintriplicates.Platecountmethodwasusedtodetermine theconcentrationofEscherichiacoli,coliformsandotherpatho- genicbacteriapresentinthecollectedgreywatersamples.
Resultsanddiscussion
Greywatertreatmentwithoutrecirculation
BasedonTable4,thelowestoperatingvolumeflowrateof10L/
minproduced the optimum treated greywater effluent quality fromthepilot-scaletreatmentsystemwithanoverallturbidity, TSS,CODremovalof80.38%,60.18%and72.59%,respectively.The treatmentperformanceofthepilot-scalesystemdeclineswiththe
increasinggreywaterfeedflowrate.Thisdeclinationintreatment performance is mainly attributed to the short contact time of greywater with the filtration mediaand ozone injector, which reducestheattachmentofcontaminantsontothemedia.
ThisoutcomewasfurthersupportedbythenegativeORPvalues andbacteriacontentofthetreatedgreywatereffluentintheclean waterholdingtankthatincreasewiththefeedflowrate.Negative ORPvalues indicatethatthe amountofozone inthe systemis insufficienttoeffectivelydisinfectthemicroorganismspresentin greywater [16]. Therefore, the pilot-scale greywater treatment systemshouldbeoperatedatthelowestflowrateof10L/minand the ozone concentration injected into the system should be optimizedinordertoobtainthemostsuitableandcost-effective ozone dosagethat can effectively disinfect themicroorganisms presentinthesystem.
Fromtheindividualperformanceof therespectivetreatment units in the pilot-scale greywater treatment system, the most apparent reduction of organic and inorganic contaminants occurredintheGACfilterwherethereductionofCODcanreach ashighas69%(refertoTable4).Mostofthesuspendedsolidswere also removed by the GAC filter. In addition, higher removal efficienciesintermsofCOD,BOD5andTSSwerealsoachievedfrom theuseofGACfilterduetotheadsorptionofcontaminantsonthe granulatedactivatedcarbonmedia[17].Theadhesionofbacteria coloniesonGACcontributedtotheformationofbiofilm[18].The formationofbiofilmcanalsobeattributedtotheaccumulationof nutrients on the GAC which indirectly promotes the grow of bacteria[18],especiallywhenthesystemisidle.However,Yinetal.
[18] suggested that the increase in the removal efficiency of contaminantscouldalsobeattributedtothebiofilmformationon theGACfilter, whichaltered thesurfacecharge densityof GAC filter.ModificationofthesurfacechargedensityoftheGACfilter,to a certain extent, enhanced the adsorption of contaminants especiallythepositivelychargedmatters[18].
In terms of bacteria removal, the pilot-scale greywater treatment system was unable to completely disinfect all the bacteria present in the treated greywater effluent for all the investigatedflowratesattheconstantozonedosingrateof10g/h.
Furthermore, the amount of bacteria remained in the treated greywater effluent also increased with the operating volume flowrate.Based onTable 4, negativedisinfectionefficiencywas observedespeciallyat highflowrates(e.g.,20L/min).Whenthe systemoperatesathighflowrate,thereispossibilitythatbacteria couldnot adhere onthe treatment unit (e.g.,SFand GAC) and flushedoutofthesystem.Thishasledtotheincreaseinbacteria concentration at the outlet of each treatment units. As the concentrationofbacteriaaccumulatesat theozonedisinfection system,theshortcontacttimeofozonewiththegreywaterdoes not alloweffective disinfection. Hence, leading tothe negative Table2
HRT(minutes)intreatmentcolumnswithrespecttodifferentprocessflowrate.
Sandfilter(ER-19M) Carbonfilter(GACcolumn)
10L/min 3.50 3.50
15L/min 2.33 2.33
20L/min 1.75 1.75
Table3
Experimentalrunsconductedonthepilotgreywatertreatmentsystem.
Run Fixedparameter Manipulatedparameter
1 O3dosingrate:10g/h(singlepassprocess) Q:10L/min
2 Q:15L/min
3 Q:20L/min
4 Q:10L/min(withoutrecirculation) O3dosingrate:5g/h
5 O3dosingrate:10g/h
6 O3dosingrate:15g/h
7 O3dosingrate:20g/h
8 Q:10L/min(recirculationloopflowrate:20L/min;O3dosingrate:10g/h) Duration:1h
9 Duration:2h
10 Q:10L/min(recirculationloopflowrate:20L/min;O3dosingrate:15g/h) Duration:1h
11 Duration:2h
disinfection efficiencies. Besides the short contact time, the presenceofbacteriainthecleanwaterholdingtankalsoimply that thereis a need tosystematicallyinvestigate ontheozone dosingrateinordertoobtainanoptimizeddosingratewhichis suitableforeffectivedisinfectionofgreywater.Therefore,subse- quentlythefeedflowratetothesystemwasfixedat10L/minwhile theozonedosingratewasvariedfrom5to20g/h.
BasedontheresultsfromTable5,disinfectionusingozonewas ineffectiveatlowerdosingrates(5and10g/h).Whentheozone dosingratewasincreased,however,thedisinfectionefficiencyof bacteriawas also significantly increased. It was found that the ozonedosingratesof15and20g/hcouldeffectivelydisinfectall the microbes that present in the treated greywater effluent.
Otherwise,theremovalefficiencyofcontaminantsinthesystem remainssimilartothoseinTable4.
Greywatertreatmentwithrecirculation
Thetreatedgreywatereffluentwasrecirculatedfordurationof 1–2hat low ozonedosagerates (5and 10g/h)and samplesof treated greywater effluent after recirculation were taken for analysis.Thetreatedgreywatereffluentqualityafterrecirculation ispresentedinTable6.Uponrecirculation,theORPvaluesofthe treatedgreywatereffluentincreasedfromanegativevaluetoORP valuesrangingfrom50to100mV(asshowninTable6),indicating that there is adequate amount of ozone in the system for disinfection.
Attheozone dosingrateof 5g/h,E.coliand othercoliforms werecompletelydisinfectedfromthetreatedgreywatereffluent within1hof recirculation.Meanwhile, thepathogenic bacteria coloniesdecreasedfrom500to150cfu/mLwhentherecirculation periodwasprolongedfrom1to2hatthesameozonedosingrate.
Thisshows that recirculationof the treated greywater effluent couldelevate the effectiveness of ozone disinfection. However, prolonged recirculation time will be required to completely disinfect the pathogenic bacteria prior to reuse at the ozone dosingrateof5g/h.Whentheozonedosingratewasincreasedto
10g/h,allbacteriapresentinthetreatedgreywatereffluentcanbe completelydisinfectedwitharecirculationperiodof1h.
Despite the increase in effectiveness of ozone disinfection system, the turbidity and TSS values of the treated greywater effluentwerefoundtoincreaseafterrecirculationperiodof1h.
TheincreaseinturbidityandTSSvaluesofthetreatedgreywater effluentafterrecirculationwasunforeseeablebecausethemulti- medium and GAC filtrationunit works to reduceturbidity and suspendedsolids.ThehigherturbidityandTSSconcentrationin thetreatedgreywatereffluentafterrecirculationwasfoundtobe mainlycontributedbythepittingofPVCtank.
Pitting of the PVC tank did not occur when the pilot-scale greywatertreatmentsystemwasoperatedwithouttherecircula- tionline.Thisisduetothefactthatozonequicklydisintegrates upongenerationandsincedisinfectiononlyoccursduringthein- lineinjectionpipeline,the residualozone in thePVCtankwas minimal.ThisisalsothepredominantreasonwhytheORPvalues inthesinglepassstudywereofnegativevalues.Whenthepilot- scale greywater treatment system was operated under the recirculationmode,thetreatedgreywatereffluentwas continu- ouslyrecirculatedthroughthein-lineinjectionpipeline,carrying moreresidualozonetothePVCtank.Thisisevidentbasedonthe positive ORP values 1–2h after recirculation of the treated greywatereffluent.Aftertheexperimentalrunsonrecirculation werecompleted,holesonthecoverandthesidePVCtankwere spotted.Thereactiveradicalsgeneratedthroughthedegradationof Table4
Overallandindividualunit’sgreywatertreatmentefficiencyatdifferentflowrates.
Flowrates(L/min)
Unitoperation Parameter 10 15 20
Sandfilter,ER-19M Turbidity(%) 47.900.49 25.001.43 13.601.13
TSS(%) 41.600.90 21.202.39 15.121.31
COD(%) 16.301.58 20.000.42 22.203.49
E.coli(%)/LRVa 61.9035.36/ 0.21-log0.08-log 28.6010.61/0.15-log0.07-log 57.1015.91/ 0.20-log0.05-log Totalcoliform(%)/LRVa 8.008.34/ 0.03-log0.03-log 27.6024.08/ 0.1-log0.08-log 12.9029.51/ 0.05-log0.11-log
Carbonfilter,GAC Turbidity(%) 62.000.39 51.000.92 45.000.15
TSS(%) 31.800.00 32.601.33 26.001.80
COD(%) 69.001.64 60.200.27 49.502.03
E.coli(%)/LRVa 11.8041.84/0.05-log0.18-log 33.3058.93/0.18-log0.55-log 87.901.94/0.92-log0.07-log Totalcoliform(%)/LRVa 52.1013.06/0.28-log0.11-log 29.7011.19/0.15-log0.07-log 15.504.00/0.07-log0.02-log
Ozonation,CTO-20 Turbidity(%) 0.900.00 1.291.47 8.760.4
TSS(%) 0.000.00 0.000.00 2.822.4
COD(%) 5.715.88 34.882.14 9.437.75
E.coli(%)/LRVa 60.0040.31/0.4-log0.65-log 0.0029.46/0.00-log0.14-log 25.0023.6/ 0.1-log0.09-log Totalcoliform(%)/LRVa 13.0628.81/0.06-log0.15-log 50.512.03/0.31-log0.02-log 29.1523.8/ 0.11-log0.08-log
Overall Turbidity(%) 80.380.02 63.670.28 56.662.76
TSS(%) 60.180.62 46.900.82 38.940.94
COD(%) 72.590.19 57.040.74 57.042.84
E.coli(%)/LRVa 42.8634.47/0.85-log0.38-log 52.3811.49/0.32-log0.10-log 76.193.54/0.62-log0.07-log Totalcoliform(%)/LRVa 54.9923.72/0.35-log0.23-log 55.610.62/0.35-log0.00-log 23.203.27/ 0.09-log0.01-log n.a:notavailable.
aLRV=logremovalvalue.
Table5
Effluentqualityundervariousozonedosingrate(feedflowrate:10L/min).
Ozonedosing(g/h)
Parameter 5 10 15 20
pH 7.0 7.0 6.9 6.9
Turbidity(NTU) 17.4 20.0 23.8 21.7
TSS(mg/L) 21.0 15.8 43.0 40.3
COD(mg/L) 18.5 22.5 37.0 35.5
E.coli(cfu/mL) 500.0 2000.0 0.0 0.0
Totalcoliform(cfu/mL) 2900.0 1400.0 0.0 0.0
Pathogenicbacteria(cfu/mL) 3400.0 1850.0 0.0 0.0
ozone would attack the PVC material, causing it to pit, thus contributingtohigherturbidityandTSSvalues.
However,theincreaseofBOD5valueswasexpectedasozoneis able to oxidize recalcitrant compounds, contributing to the increasebiodegradabilityofthetreatedgreywatereffluent[19].
SincepittingofthePVCtankwasobservedafterrecirculation,this wouldhavemostlikelycontributedtotheincreaseinCODvalues aftertreatment.
Cost-benefitanalysisofthepilot-scalegreywatertreatmentsystem
In overview, it was documented that Malaysians consume freshwaterofapproximately226L/capita/daywhereatleast41%of it ends up as greywater [20]. When this pilot-scale greywater treatmentsystemisoperatedataflowrateof10L/mincontinu- ously,it is capable of treating 14.4m3 of greywater daily. This impliesthatthepilot-scalesystemhasthepotentialtoconserve drinking water for at least 140 person (28 households with 5 personin a family)for other potableactivities,from usingthe treatedanddisinfectedgreywatereffluent.Theamountofdrinking water that can be conserved using this greywater treatment systemwillbesignificantifthispilot-scalesystemisfurtherbeing scaled-up.
However, it is also of great importance to evaluate the treatment cost to ensure the competitiveness and long-term sustainabilityofthegreywatertreatmentsystem.Table7shows thecoststhatareinvolvedintheadoptionandoperationofthe greywatertreatmentsystemevaluatedinthisstudy.Therearetwo schemeswhich are beingconsideredin thecostevaluation: (i) singlepasstreatmentanddisinfectionataflowrateof10L/hand ozone dosage of 15g/h and (ii) greywater treatment with 1h recirculationatafeedflowrateof10L/h,recirculationflowrateof 20L/h and ozone dosing rate of 10g/h. Since the greywater treatment system is targeted for installation in future green buildings,thewatertarifftakenasabenchmarkforcomparisonof
treatmentcostandelectricitytariffforevaluationofoperational costarebasedonthedomesticbuildingtariffinMalaysia.
The operational cost of the pilot-scale greywater treatment systemtakesintoaccountofthecosttooperatethefeedpump, recirculationpumpaswellasozonegeneration.Theoperational costwasevaluatedbasedonanaverageoperationaltimeof324 dayswith1 month ofdowntimefor maintenance andcleaning annually.Sincethisisasemi-continuoussystemduetointermit- tentsupplyofgreywater,thetotaloperationalhoursis10h/dayfor a singlepass systemand 16h/dayfora recirculationsystem to process6.0m3ofgreywaterdaily(i.e.,10hoftreatmentand6hof recirculation).
Based onTable7,theoperationofthis pilot-scalegreywater treatment system using Scheme i couldpotentially save up to USD464.64/year.Thesavingsofutilitybillswouldbegreaterwith theincreaseintreatmentcapacity.Itwasfoundthatoperatingthe pilot-scalegreywatertreatmentsystemwouldenableconsumers to have greater savings if the system was operated under Scheme(i).Thisisduetothefactthattheperiodofoperationis shorter(i.e.,fasterturnover)forsuchsystemwithoutrecirculation.
However,operationunderScheme(ii)canbeadvantageoustocope withsuddenspikeintheamountofbacteriaintothesystem.The recirculationoftreatedgreywatereffluentcanensurethatbacteria arecompletelydisinfectedpriortoreuse.
In addition, the specific energy of this system is 1.09 and 1.68kWh/m3forSchemes(i)and(ii),respectively.Itisinteresting to note that the specific energy of these two schemes were comparabletothoseofacentralizedwastewatertreatmentplant (Pimpama-Coomera, Gold Coast), with a specific energy of 1.80kWh/m3[21].Thisshowsthatthereisdefinitelyaprospect to implement such system in high-density residential units at betterenergeticcost.Theimplementationofdecentralizedgrey- watertreatmentsystemcouldalsohelptoreducetheincreasing burden ofcentralizedsewage treatmentplantsdue toinfluxof populationinurbanareas.
Table7
Operationalandtreatmentcostofpilotgreywatertreatmentsystem.
Parameters
Maximumsystemcapacity(continuoussystem) 14.4m3/day
TreatmentcapacityofSchemes(i)and(ii) 6.0m3/day
Watertariff(domestic–condominium/Apartments) USD0.28a/m3(SYABAS,2014)
Averageelectricitytariff(Domestic) USD0.09a/kWh(TenagaNasional,2014)
Electricityconsumption(Scheme(i)) 6.55kWh/day
Electricityconsumption(Scheme(ii)) 10.09kWh/day
Operationalcost(electricitytooperatepumpsandozonegenerator) Scheme(i):USD0.58a/day Scheme(ii):USD0.90a/day
Maintenanceandcleaning Scheme(i)and(ii):USD112.30a/year
Totaltreatmentcost(operational+maintenanceandcleaningcost) Scheme(i):USD0.15a/m3 Scheme(ii):USD0.21a/m3
Savings(watertariff totaltreatmentcost) Scheme(i):USD0.23a/m3
Scheme(ii):USD0.18a/m3
aExchangerateofRM1toUSD0.28applied(retrievedon:11am,12January2015).
Table6
Effluentqualityundervariousozonedosingrateandrecirculationduration.
Parameter Ozonedosing(g/h)(recirculationduration)/ORP(mV)
5(1h)/50 5(2h)/92 10(1h)/64 10(2h)/100
pH 7.11 7.19 6.96 6.93
Turbidity(NTU) 10.10 9.38 16.90 16.80
TSS(mg/L) 15.00 15.00 27.30 26.30
COD(mg/L) 20.00 20.30 26.00 50.00
BOD5(mg/L) 3.00 0.75 4.50 0.00
E.coli(cfu/mL) 0.00 0.00 0.00 0.00
Totalcoliform(cfu/mL) 0.00 0.00 10100.00 450.00
Pathogenicbacteria(cfu/mL) 500.00 150.00 0.00 0.00
The outcome of this cost-benefit analysis showed that the implementationofgreywater treatmentsystem in high-density residentialunitscanbebeneficialduetothehigherwatertariffs imposedcomparedtodomesticwaterusageindetachedhouses and more efficient energy consumption. A simple greywater treatmentsystem proposedinthis studycouldproducetreated greywatereffluentthatmeetsthestandardfornon-potableusage, reduce freshwater consumption as well as reduce utility cost withinthebuildingpremise.
Conclusion
Inconclusion,theimplementationofthisgreywaterreclama- tionsystemcanmitigatewatershortageandreliefwaterstress.
Reclaimedgreywatercanreducelargeamountoffreshwaterused innon-potableactivitiessuchastoiletflushing,gardenwatering andoutdoorwashing.Subsequently,thetreatmentperformanceof this pilot-scale greywater treatment system was successfully assessed.It wasfoundthat atleast15g/hof ozonedosagewas required to completely disinfect the bacteria present in the greywaterwithoutrecirculation.Meanwhile,theozonedosingrate can be further reduced to 10g/h for complete disinfection by recirculatingtreatedgreywaterfor1h. Calculationshaveshown thatinstallationofgreywatertreatmentsystemcouldpotentially reduce the utility costs borne by the consumers staying in domestichigh-risebuildings.
Acknowledgements
TheauthorswouldliketoextendtheirgratitudetoBacteriaFree Water Engineering (M) Sdn. Bhd. for the pilot-scalegreywater treatmentsystem usedin thisstudyand themonetarysupport providedbythiscompanythroughoutthisproject.Also,wewould liketoacknowledgetheAdvancedEngineeringPlatformofMonash University,Malaysiaforthefinancialsupportinthisproject.
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