ENVIRONMENT
050 How It Works http://www.howitworksdaily.com
I
n countrieswherewaterisreadilyavailableto
us,wecansometimestakeit forgranted.Ithas
somanyuses,eitherpersonallyinourown
homes,aspartofmostindustrialprocessesorin
agriculturetohelpusgrowourfood.However,
oncewehaveutilisedthiswater,it becomes
contaminatedandcanbea dangertoourhealth.
Whatdowedowiththewaterthen?
Most wastewater follows the same route as it
is directed underground and into treatmentplants.Hav inglearnedfromprev iousissues
throughouthistory,weknowthatdumping
sewagebackintoriversandoceansuntreated
hasdireconsequencesforeveryone’shealth.
Sewagesystemsaretaskedwiththejobof
remov ingdebris,fromlargeplasticobjectsthat
havefoundtheirwayintodrainstosmaller
mineralparticlessuchasgritorstones.Once
contaminant-free, the water is returned to
nature to repeat the cycle.Fromthemomentyouflushthetoiletorpullthepluginthe
sink,followthejourneyofwastewater
Where does our
sewage go?
Sewage types
Whilesewageis generallyclassedunder
theoneterm,it isn’tallthesame.There
arethreetypes:domesticsewage,
industrialsewageandstormsewage.
Wastewaterleavingourhousesis the
domestictype,industrialis thewaste
productofchemicalandmanufacturing
processesandstormsewageis runoff
rainwatercollectedinpipes.
Treatingdomesticwastewatercanbe
themostdifficultastherearea wider
rangeofimpuritiespossible,makingit
muchmoreunpredictable.Meanwhile,
industrialwastehasmoreeasilydetected
chemicalcompounds,dependingonthe
industrialprocesstakingplace.
Stormsewageusuallyholdsa high
concentrationoforganicmatterasit
travelsalongtheground.Todetect
organicmaterial,thebiochemicaloxygen
demand(BOD)is tested.Thisis the
amountofoxygenmicroorganisms
needtodecomposethematter,andthe
highertheBODthehigherthevolumeof
organicsubstances.Somewastewatersystemscan’thandlethelarge
volumesofstormsewage,sothiswateroften
bypasses in large pipesThere are over 7,000
sewage treatment plants
in England and Wales© Getty© Alamy