Usinggreywatertoflushtoiletssaveswaterbutsolidbuild-upcouldharmthepipes,especiallyduringtimesofdroughtwhenhouseholdersflushlessoften.
AnewpaperintheJournalofWaterProcessEngineeringbyUniversityofCapeTown(UCT)researchersWaseefaEbrahimandDrDyllonRandallofferssomepracticalsolutionsforwatersaverstoavoiddamagingtheirsanitationinfrastructure.
Theseguidelinesareapplicableforwater-consciousCapetonianswhoflushwithgreywaterfromhandwashing(tapwaterwithsoap)orfromshowering(tapwaterwithsoapandshampoo).
Thepaperisinresponsetothedevastating2015–2018droughtanditsaftermathwhencitizensgotbehindcity-widewatersavingsinitiativesandadoptedthecatchphrase“Ifit’syellowletitmellow”,flushinglessandusinggreywatertodoso.
Theresultwasamorethan50%reductioninwaterusagecomparedwithpre-droughtconditions.Waterdemanddroppedfrom1200MLadayinFebruary2015to500MLadayinFebruary2018,asignificantachievementforacityof4.1millionpeople,saidtheauthors.
“Buttheimmediatetoiletinfrastructure,suchasthetrap,siphonandpipingconnectiontothesewernetwork,couldbecomeclogged.”
EbrahimandRandallcalculatedthatthecity’swaste-watertreatmentplantscouldcopewiththeadditionalestimated893tonsofsolidsaddedtothesystemfromgrey-waterflushingandallowingurinetostagnateintoiletbowls.
Buttheimmediatetoiletinfrastructure,suchasthetrap,siphonandpipingconnectiontothesewernetwork,couldbecomecloggedbysolidsbecauseofprecipitationduringreducedflushingperiods.
Labtests
IntheirlabteststheyusedcleaningproductstypicallyfoundinSouthAfricanhouseholdstoprovidearealisticproductrepresentationforthesyntheticgreywater,andincludedsoap,shampoo,vinegarandbleach.Bytestingthesolutionsbeforeandafterflushing,theyrecordedthemostsignificantcompositionalchangesforanalysis.
Theyfoundthatsomesolidsthathadformedduringtheirexperimentscouldnotberemovedfromequipmentsimplybyrinsingwithwater.Instead,equipmenthadtobecleanedusingaweakacidsolution.
“Thissuggeststhatsolidscouldserveasnucleionwhichnewsolidsgrow,”theynoted.
“Thiscouldleadtosolidbuild-upinthepipes,reducingtheircapacityandlifespan.”
Thekeyparameterthatinfluencesthebuild-upofsolidsisthepHofthesolution,saidRandall.Conventionally,flushingatoiletbowlwithtapwateraftereachtoiletusewilldecreasethepHandthuslimitsolidbuild-up.
“However,limitedtoiletflushingandflushingwithgreywater,whichinherentlyhasahighpH,willincreasethepHofthesolution.ItisthisincreaseinsolutionpHthatresultsinsolidformationfromthestagnatingurine.”
EbrahimandRandallfoundthatthemaximumpHofthesolutioninthetoiletbowlwasreachedinjusttwodayswhenusinggreywatertoflush,whichresultedinexcessivesolidformation.
Theysayfurtherresearchisurgentifcostlypipingandinfrastructurereplacementistobeavoided.
Guidelinesforwatersavers
Intheirpaper,theresearchershavelistedfiverecommendations:
Randall,whoisalsopartofUCT’sFutureWaterInstitute,hopesthatfuturehouseholdswillhavewaterlessurinals,alsodesignedtorecovernutrientsfromurine.
“Thiswouldlimitissuesassociatedwithstagnatingurineintoiletbowlsduringtimesofreducedtoiletflushingwhilealsosavingwaterandrecoveringvaluableresources.”
Headded:“Thesocialacceptanceandtechnicalfeasibilityatahouseholdlevelwouldhavetoalsobeassessedthoughforthismethodtobeadopted.”
Lookingahead,Ebrahimsaidsocietyismovingtowardsclosingthelooponthewatercyclebyreusinggreywaterandreducingwasteingeneral.
“It[thiswork]wasinspiredbytheCapeTown[water]crisisbutultimatelywe’relookingtowardswhatthesanitationofthefuturewilllooklike.”
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