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1、 Somewatersourcescontaindisease-causingorganismswhichneedtoberemovedorkilledbeforethewaterissafetodrink.Ifcarefullyundertakenandmonitored,disinfectionisaneffectivemeansofremovingsuchorganisms.Chlorineisthemostwidelyuseddisinfectant,andonewhichisoftenthe
2、mostreadilyavailable.Thistechnicalbriefdescribesamethodofcalculatingthedoseofchlorinerequiredtodisinfectsmallcommunitywatersupplies.Whydisinfect?ChlorinedemandandresidualWatertreatmentprocessessuchasstorage,sedimenta-Whenchlorineisaddedtoawatersource,itpurifiesth
3、etion,andsandfiltrationwillreducethecontentofdisease-waterbydamagingthecellstructureofbacterialpollut-causingorganismsinwater,butwillnotleaveitcom-ants,therebydestroyingthem.Theamountofchlorinepletelyfreeofsuchorganisms.Disinfection,whenap-neededtodothisiscalledt
4、hechlorinedemandofthepliedandcontrolledproperly,isthemostpracticalandwater.Thechlorinedemandvarieswiththeamountofeffectivemeansofremovingsuchorganisms.impuritiesinthewater.ItisimportanttorealisethatthechlorinedemandofawatersourcewillvaryasthequalityMethodsofdisin
5、fectionofthewatervaries.Boilingwatermaybeeffectiveasamethodofdisinfection,Theaimofchlorinationistosatisfythechlorinedemandbutitisnotpracticableforlargequantities.Sunlightcanalsoofthewatersource.Oncethedemandhasbeensatisfied,actasanaturalmethodofdisinfection,butit
6、isdifficulttoanyexcesschlorineabovethelevelneededtosatisfythecontrolandmanage.Forthesereasons,chemicaldisinfect-demandremainsasaresidualofchlorine(chlorineants(especiallychlorineandchlorinecompounds)areresidual)inthesupply.used.Iodinemayalsobeusedasadisinfectant,
7、butitisIfasupplyistobeadequatelydisinfected,therefore,usuallymoreexpensivethanchlorinecompounds.thereshouldbeachlorineresidualinthesupply,sothatChlorinecompoundswilldestroydisease-causingorgan-thereisthecapacitytocopewithanysubsequentbacte-ismsquickly—usuallyafte
8、r30minutes.Theyarewidelyrialcontamination.Thechlorineresidualshouldgenerallyusedandarerelativelyinexpensive.Ifcarefullyapplied,beintherange0.3to0.5mgofchlorine
