VII. Water TreatmentVII. Water TreatmentA. Treatment of wastewater andA. Treatment of wastewater andB. Treatment of drinking waterB. Treatment of drinking water
Objectives - students should:Objectives - students should:List and describe treatment methods forList and describe treatment methods forwastewater.wastewater.List and describe treatment methods forList and describe treatment methods fordrinking water.drinking water.Compare and contrast treatment methodsCompare and contrast treatment methodsand goals of wastewater and drinkingand goals of wastewater and drinkingwater.water.
Justification for wastewaterJustification for wastewatertreatment:treatment:Pollution from sewage is a primaryPollution from sewage is a primaryenvironmental health hazardenvironmental health hazard(wastewater effluent).(wastewater effluent).The purpose of municipal wastewaterThe purpose of municipal wastewatertreatment is to limit pollution of thetreatment is to limit pollution of thereceiving watercourse.receiving watercourse.The receiving watercourse may also beThe receiving watercourse may also bea source of drinking water.a source of drinking water.
Goals of wastewater treatment:Goals of wastewater treatment:Reduction ofReduction of organic loadorganic load of theof thewastewater effluent to limitwastewater effluent to limiteutrophication (BOD, COD limits),eutrophication (BOD, COD limits),Reduction ofReduction of microbiologicalmicrobiologicalcontaminationcontamination that may transmitthat may transmitinfectious disease.infectious disease.
Municipal wastewater treatmentMunicipal wastewater treatmentfacility and regulationsfacility and regulationsMunicipal wastewater treatment facilities, orMunicipal wastewater treatment facilities, or“Publicly Owned Treatment Works” (POTWs), or“Publicly Owned Treatment Works” (POTWs), or“Water Reclamation Districts” are designed to“Water Reclamation Districts” are designed toreduce environmental health risks of untreatedreduce environmental health risks of untreatedwastewater.wastewater.Levels of treatment required are based on NPDESLevels of treatment required are based on NPDESregulations.regulations.
Wastewater treatmentWastewater treatmentprocesses:processes:PreliminaryPreliminary treatment is a physicaltreatment is a physicalprocess that removes large contaminants.process that removes large contaminants.PrimaryPrimary treatment involves physicaltreatment involves physicalsedimentation of particulates.sedimentation of particulates.SecondarySecondary treatment involves physical andtreatment involves physical andbiological treatment to reduce organicbiological treatment to reduce organicload of wastewater.load of wastewater.TertiaryTertiary or advanced treatments.or advanced treatments.
Nitrification-denitrification process toNitrification-denitrification process toremove N and Premove N and PFiltrationFiltrationCarbon AdsorptionCarbon AdsorptionConstructed (Man-made] WetlandConstructed (Man-made] WetlandTertiary or Advanced TreatmentTertiary or Advanced Treatment
More than 25% of all households in the U.S. areMore than 25% of all households in the U.S. areserved by on-site treatment systems.served by on-site treatment systems.About 3 billion gallons of wastewater isAbout 3 billion gallons of wastewater isdischarged each day to on-site wastewaterdischarged each day to on-site wastewatertreatment systems.treatment systems.Potential disease transmission risks throughPotential disease transmission risks throughwastewater should be limited.wastewater should be limited.On-site wastewaterOn-site wastewatertreatmenttreatment
Septic systemsSeptic systems typically consist of:typically consist of:A septic tankA septic tank (concrete, with inlet and outlet,(concrete, with inlet and outlet,baffles, and removable top for cleaning),baffles, and removable top for cleaning),which collects and holds waste,which collects and holds waste,A drain fieldA drain field oror tile fieldtile field (plastic or tile pipe(plastic or tile pipewith outlets) which allows wastewater effluentwith outlets) which allows wastewater effluentto infiltrate slowly into soils.to infiltrate slowly into soils.Plumbing connectionsPlumbing connections..Typical septic system design:Typical septic system design:
Periodic summeryPeriodic summeryTreatment of wastewater is necessary to protectTreatment of wastewater is necessary to protectthe environment and preserve the quality of waterthe environment and preserve the quality of waterfor drinking.for drinking.Treatment of municipal wastewater typicallyTreatment of municipal wastewater typicallyincludes preliminary, primary treatment,includes preliminary, primary treatment,secondary treatment, and tertiary treatment.secondary treatment, and tertiary treatment.On-site wastewater treatment is facilitated byOn-site wastewater treatment is facilitated byseptic tank systems.septic tank systems.
B. Drinking water treatment:B. Drinking water treatment:ClarificationClarification - primarily a- primarily a physicalphysicalprocess, but may be aided by addition ofprocess, but may be aided by addition ofchemicals.chemicals.FiltrationFiltration - also primarily- also primarily physicalphysical, but, butchemicals may aid the process.chemicals may aid the process.DisinfectionDisinfection - typically a- typically a chemicalchemicalprocess that reduces pathogenicprocess that reduces pathogenicmicroorganisms.microorganisms.
B1. Clarification of drinkingB1. Clarification of drinkingwater:water:Clarification removes particulates thatClarification removes particulates thatcontribute to turbidity and contaminationcontribute to turbidity and contaminationof water.of water.Clarification is aided by chemicals whichClarification is aided by chemicals whichcause particulates to aggregate,cause particulates to aggregate,precipitate, and form sediment (sludge).precipitate, and form sediment (sludge).
B2. Filtration:B2. Filtration:Separate nonsettleable solids from water.Separate nonsettleable solids from water.Combined with coagulation/clarification,Combined with coagulation/clarification,filtration can remove 84%-96% turbidity,filtration can remove 84%-96% turbidity,coliform bacteria 97-99.95%, and >99%coliform bacteria 97-99.95%, and >99%Giardia.Giardia.
Rapid filtrationRapid filtration - uses gravity (faster- uses gravity (fasterflow).flow).Slow filtrationSlow filtration - uses gravity [slower- uses gravity [slowerflow].flow].Pressure sand filtersPressure sand filters -use water-use waterpressure.pressure.• Diatomaceous earth (DE) filtrationDiatomaceous earth (DE) filtrationMicrostrainingMicrostraining - uses fine steel fabric- uses fine steel fabric(sometimes used prior to other filtrations).(sometimes used prior to other filtrations).Type of FiltrationType of Filtration
Filter MediaFilter MediaFilter media should be:Filter media should be:• coarse enough to retain large quantities of floccoarse enough to retain large quantities of floc• sufficiently fine to prevent passage of suspended solidssufficiently fine to prevent passage of suspended solids• deep enough to allow relative long filter runsdeep enough to allow relative long filter runsGranular-medium filters (Rapid Sand Filters]Granular-medium filters (Rapid Sand Filters]• Anthracite on the very top (least dense),Anthracite on the very top (least dense),• fine sand on top of supporting coarse sand(less dense),fine sand on top of supporting coarse sand(less dense),which lays on top ofwhich lays on top of• gravel layer (highest density).gravel layer (highest density).
Cleaning (backwashing) filtersCleaning (backwashing) filtersDetermination of how often to back-washDetermination of how often to back-washcan be made on the basis of:can be made on the basis of:• Head loss (pressure loss),Head loss (pressure loss),• Loss of water quality (e.g., increased turbidity),Loss of water quality (e.g., increased turbidity),oror• Time since last backwash.Time since last backwash.
Backwashing processBackwashing processWater flow is reversed through the filterWater flow is reversed through the filterbed.bed.• TheThe raterate of backwash is designed to partiallyof backwash is designed to partiallyexpand (fluidize) the filter bed.expand (fluidize) the filter bed.• Suspended matter is removed bySuspended matter is removed by shearshear forcesforcesas the water moves through the fluidized bed.as the water moves through the fluidized bed.• AdditionalAdditional cleaning occurs when particles ofcleaning occurs when particles ofthe bed abrade against each other.the bed abrade against each other.
Flow control through filtersFlow control through filtersConstant-rate filtrationConstant-rate filtration• Flow rate is controlled by limiting theFlow rate is controlled by limiting thedischarge rate, limiting the rate of inflow by adischarge rate, limiting the rate of inflow by aweir, orweir, or• by pumping or use of influent flow-splittingby pumping or use of influent flow-splittingweir.weir.Declining-rate filtrationDeclining-rate filtration• Rate of flow declines as the rate of head lossRate of flow declines as the rate of head lossbuilds (influent- or effluent-controlled).builds (influent- or effluent-controlled).
Periodic Summary:Periodic Summary:Drinking water treatment typicallyDrinking water treatment typicallyinclude clarification, filtration andinclude clarification, filtration anddisinfection.disinfection.Drinking water treatment should makeDrinking water treatment should makewater both potable and palatable.water both potable and palatable.Wastewater and drinking waterWastewater and drinking watertreatment processes are similar intreatment processes are similar inseveral ways.several ways.
VII. Water TreatmentVII. Water TreatmentB3. Disinfection of drinkingB3. Disinfection of drinkingwaterwater
Objectives - students should:Objectives - students should:Define and give examples of types ofDefine and give examples of types ofdisinfection techniques for drinkingdisinfection techniques for drinkingwater.water.Distinguish between physical andDistinguish between physical andchemical disinfection techniques.chemical disinfection techniques.Evaluate the safety, cost, effectiveness,Evaluate the safety, cost, effectiveness,and popularity of various disinfectionand popularity of various disinfectiontechniques.techniques.
Types of disinfection:Types of disinfection:Physical disinfection techniques includePhysical disinfection techniques includeboiling and irradiation with ultravioletboiling and irradiation with ultravioletlight.light.Chemical disinfection techniques includeChemical disinfection techniques includeadding chlorine, bromine, iodine, and ozoneadding chlorine, bromine, iodine, and ozoneto water.to water.
Physical disinfection (boiling):Physical disinfection (boiling):Boiling kills vegetative bacterial cells, butBoiling kills vegetative bacterial cells, butspores, viruses, and some protozoa mayspores, viruses, and some protozoa maysurvive long periods of boiling.survive long periods of boiling.Boiling may also volatilize VOC’s.Boiling may also volatilize VOC’s.Boiling is an effective method for smallBoiling is an effective method for smallbatches of water during water emergencies.batches of water during water emergencies.Boiling is prohibitivelyBoiling is prohibitively expensiveexpensive for largefor largequantities of water.quantities of water.
Physical disinfectionPhysical disinfection(UV radiation):(UV radiation):Ultraviolet radiation is an effective andUltraviolet radiation is an effective andrelatively safe disinfection method, but isrelatively safe disinfection method, but isrelatively expensive and not widely used.relatively expensive and not widely used.UV light disrupts DNA of microbial cells,UV light disrupts DNA of microbial cells,preventing reproduction.preventing reproduction.Specific wavelengths, intensities,Specific wavelengths, intensities,distances, flow rates, and retention timesdistances, flow rates, and retention timesare required.are required.
Chemical disinfection:Chemical disinfection:Chemicals added to water for disinfectionChemicals added to water for disinfectioninclude chlorine, bromine, and iodine.include chlorine, bromine, and iodine.Bromine is not recommended for drinkingBromine is not recommended for drinkingwater disinfection, but may be used forwater disinfection, but may be used forpool water.pool water.Iodine is sometimes used for drinkingIodine is sometimes used for drinkingwater disinfection, but causes a badwater disinfection, but causes a badaftertaste.aftertaste.
Chlorine disinfection:Chlorine disinfection:Chlorination is a cheap, effective, relativelyChlorination is a cheap, effective, relativelyharmless (and therefore most popular)harmless (and therefore most popular)disinfection method.disinfection method.Chlorine is added as a gas or hypochloriteChlorine is added as a gas or hypochloritesolution.solution.Hypochlorous acid and hypochlorite ionsHypochlorous acid and hypochlorite ionsform in solution, which are strong chemicalform in solution, which are strong chemicaloxidants, and kill microbes.oxidants, and kill microbes.
Chlorine disinfection (cont.):Chlorine disinfection (cont.):Combined chlorine is the proportion thatCombined chlorine is the proportion thatcombines with organic matter.combines with organic matter.Free chlorine is the amount thatFree chlorine is the amount that remainsremainsto kill microbes in the distribution systemto kill microbes in the distribution system(0.5 ppm, 10 min.)(0.5 ppm, 10 min.)Total chlorine is the combined concen-Total chlorine is the combined concen-tration of combined and free chlorine.tration of combined and free chlorine.
Disinfection By-Products (DBPs)Disinfection By-Products (DBPs)Chlorine (or bromine or iodine) + “precursors”Chlorine (or bromine or iodine) + “precursors”(organic compounds) = THM(Trihalomethanes)(organic compounds) = THM(Trihalomethanes)• eg. Chloroform (CHCleg. Chloroform (CHCl33), Bromoform (CHBr), Bromoform (CHBr33), Iodoform), Iodoform(CHI(CHI33), chlorobromoform (CHBrCl), chlorobromoform (CHBrCl22), Bromochloroform), Bromochloroform(CHBr(CHBr22Cl), Bromoidodform (CHBrCl), Bromoidodform (CHBr22I), etc.I), etc.THMs are carcinogenicTHMs are carcinogenicChoroamine disinfection reduce THMs productionChoroamine disinfection reduce THMs productiondue to preferential reaction of chlorine withdue to preferential reaction of chlorine withammoniaammonia
Ozonation:Ozonation:Ozone (OOzone (O33) is an effective, relatively) is an effective, relativelyharmless disinfection method, but isharmless disinfection method, but isexpensive (and therefore less popular thanexpensive (and therefore less popular thanchlorine).chlorine).Ozone is a strong oxidant, that producesOzone is a strong oxidant, that produceshydroxyl free radicals that react withhydroxyl free radicals that react withorganic and inorganic molecules in waterorganic and inorganic molecules in waterto kill microbes.to kill microbes.
Summary:Summary:Disinfection is the destruction ofDisinfection is the destruction ofmicroorganisms in drinking water to safemicroorganisms in drinking water to safelevels.levels.Disinfection techniques include physicalDisinfection techniques include physical(boiling, ultraviolet light) and chemical(boiling, ultraviolet light) and chemicalmethods (chlorine, bromine, iodine, andmethods (chlorine, bromine, iodine, andozone).ozone).