VII. Water Treatment A. Treatment of wastewater and B. Treatment of drinking water.

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VII. Water Treatment VII. Water Treatment A. Treatment of A. Treatment of wastewater and wastewater and B. Treatment of B. Treatment of drinking water drinking water

Transcript of VII. Water Treatment A. Treatment of wastewater and B. Treatment of drinking water.

Page 1: VII. Water Treatment A. Treatment of wastewater and B. Treatment of drinking water.

VII. Water TreatmentVII. Water Treatment

A. Treatment of wastewater A. Treatment of wastewater andand

B. Treatment of drinking B. Treatment of drinking waterwater

Page 2: VII. Water Treatment A. Treatment of wastewater and B. Treatment of drinking water.

Objectives - students Objectives - students should:should:

List and describe treatment List and describe treatment methods for wastewater.methods for wastewater.

List and describe treatment List and describe treatment methods for drinking water.methods for drinking water.

Compare and contrast treatment Compare and contrast treatment methods and goals of wastewater methods and goals of wastewater and drinking water.and drinking water.

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Justification for Justification for wastewater treatment:wastewater treatment:

Pollution from sewage is a primary Pollution from sewage is a primary environmental health hazard environmental health hazard (wastewater effluent).(wastewater effluent).

The purpose of municipal The purpose of municipal wastewater treatment is to limit wastewater treatment is to limit pollution of the receiving pollution of the receiving watercourse.watercourse.

The receiving watercourse may also The receiving watercourse may also be a source of drinking water.be a source of drinking water.

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Goals of wastewater Goals of wastewater treatment:treatment:

Reduction of Reduction of organic loadorganic load of of the wastewater effluent to the wastewater effluent to limit eutrophication (BOD, limit eutrophication (BOD, COD limits),COD limits),

Reduction of Reduction of microbiological microbiological contaminationcontamination that may that may transmit infectious disease.transmit infectious disease.

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Municipal wastewater Municipal wastewater treatment facility and treatment facility and regulationsregulations

Municipal wastewater treatment Municipal wastewater treatment facilities, or “Publicly Owned Treatment facilities, or “Publicly Owned Treatment Works” (POTWs), or “Water Reclamation Works” (POTWs), or “Water Reclamation Districts” are designed to reduce Districts” are designed to reduce environmental health risks of untreated environmental health risks of untreated wastewater.wastewater.

Levels of treatment required are based Levels of treatment required are based on NPDES regulations.on NPDES regulations.

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Wastewater Treatment SchemeWastewater Treatment Scheme

Preliminary Secondary

WW influent

WW effluent

sludge

Primary Tertiary

Disinfectant

Sludge Treatment and Disposal

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Wastewater treatment Wastewater treatment processes:processes:

PreliminaryPreliminary treatment is a physical treatment is a physical process that removes large process that removes large contaminants.contaminants.

PrimaryPrimary treatment involves physical treatment involves physical sedimentation of particulates.sedimentation of particulates.

SecondarySecondary treatment involves treatment involves physical and biological treatment to physical and biological treatment to reduce organic load of wastewater.reduce organic load of wastewater.

TertiaryTertiary or advanced treatments. or advanced treatments.

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Nitrification-denitrification process Nitrification-denitrification process to remove N and Pto remove N and P

FiltrationFiltration Carbon AdsorptionCarbon Adsorption Constructed (Man-made] WetlandConstructed (Man-made] Wetland

Tertiary or Advanced Tertiary or Advanced TreatmentTreatment

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More than 25% of all households in the More than 25% of all households in the U.S. are served by on-site treatment U.S. are served by on-site treatment systems.systems.

About 3 billion gallons of wastewater is About 3 billion gallons of wastewater is discharged each day to on-site discharged each day to on-site wastewater treatment systems.wastewater treatment systems.

Potential disease transmission risks Potential disease transmission risks through wastewater should be limited.through wastewater should be limited.

On-site wastewater On-site wastewater treatmenttreatment

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Septic systems Septic systems typically consist of:typically consist of: A septic tankA septic tank (concrete, with inlet and (concrete, with inlet and

outlet, baffles, and removable top for outlet, baffles, and removable top for cleaning), which collects and holds waste,cleaning), which collects and holds waste,

A drain fieldA drain field oror tile field tile field (plastic or tile (plastic or tile pipe with outlets) which allows wastewater pipe with outlets) which allows wastewater effluent to infiltrate slowly into soils.effluent to infiltrate slowly into soils.

Plumbing connectionsPlumbing connections..

Typical septic system Typical septic system design:design:

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Periodic summeryPeriodic summery

Treatment of wastewater is necessary to Treatment of wastewater is necessary to protect the environment and preserve the protect the environment and preserve the quality of water for drinking.quality of water for drinking.

Treatment of municipal wastewater Treatment of municipal wastewater typically includes preliminary, primary typically includes preliminary, primary treatment, secondary treatment, and treatment, secondary treatment, and tertiary treatment.tertiary treatment.

On-site wastewater treatment is facilitated On-site wastewater treatment is facilitated by septic tank systems.by septic tank systems.

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B. Drinking water B. Drinking water treatment:treatment:

ClarificationClarification - primarily a - primarily a physicalphysical process, but may be aided by process, but may be aided by addition of chemicals.addition of chemicals.

FiltrationFiltration - also primarily - also primarily physicalphysical, , but chemicals may aid the process.but chemicals may aid the process.

DisinfectionDisinfection - typically a - typically a chemicalchemical process that reduces pathogenic process that reduces pathogenic microorganisms.microorganisms.

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B1. Clarification of B1. Clarification of drinking water:drinking water:

Clarification removes particulates that Clarification removes particulates that contribute to turbidity and contribute to turbidity and contamination of water.contamination of water.

Clarification is aided by chemicals Clarification is aided by chemicals which cause particulates to aggregate, which cause particulates to aggregate, precipitate, and form sediment precipitate, and form sediment (sludge).(sludge).

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B2. Filtration:B2. Filtration:

Separate nonsettleable solids Separate nonsettleable solids from water.from water.

Combined with Combined with coagulation/clarification, filtration coagulation/clarification, filtration can remove 84%-96% turbidity, can remove 84%-96% turbidity, coliform bacteria 97-99.95%, and coliform bacteria 97-99.95%, and >99% Giardia.>99% Giardia.

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Rapid filtration Rapid filtration - uses gravity (faster - uses gravity (faster flow).flow).

Slow filtration Slow filtration - uses gravity [slower flow].- uses gravity [slower flow]. Pressure sand filtersPressure sand filters-use water pressure.-use water pressure.

• Diatomaceous earth (DE) filtrationDiatomaceous earth (DE) filtration MicrostrainingMicrostraining - 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

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Filter MediaFilter Media

Filter 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 sufficiently fine to prevent passage of suspended

solidssolids• deep enough to allow relative long filter runsdeep enough to allow relative long filter runs

Granular-medium filters (Rapid Sand Granular-medium filters (Rapid Sand Filters]Filters]• Anthracite on the very top (least dense),Anthracite on the very top (least dense),• fine sand on top of supporting coarse sand(less fine sand on top of supporting coarse sand(less

dense), which lays on top of dense), which lays on top of • gravel layer (highest density).gravel layer (highest density).

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Cleaning (backwashing) Cleaning (backwashing) filtersfilters

Determination of how often to Determination of how often to back-wash can be made on the back-wash can be made on the basis of:basis of:• Head loss (pressure loss),Head loss (pressure loss),• Loss of water quality (e.g., increased Loss of water quality (e.g., increased

turbidity), orturbidity), or• Time since last backwash.Time since last backwash.

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Backwashing processBackwashing process

Water flow is reversed through the Water flow is reversed through the filter bed.filter bed.• The The raterate of backwash is designed to of backwash is designed to

partially expand (fluidize) the filter bed.partially expand (fluidize) the filter bed.• Suspended matter is removed by Suspended matter is removed by shearshear

forces as the water moves through the forces as the water moves through the fluidized bed.fluidized bed.

• AdditionalAdditional cleaning occurs when particles cleaning occurs when particles of the bed abrade against each other.of the bed abrade against each other.

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Flow control through filtersFlow control through filters

Constant-rate filtrationConstant-rate filtration• Flow rate is controlled by limiting the Flow rate is controlled by limiting the

discharge rate, limiting the rate of discharge rate, limiting the rate of inflow by a weir, orinflow by a weir, or

• by pumping or use of influent flow-by pumping or use of influent flow-splitting weir.splitting weir.

Declining-rate filtrationDeclining-rate filtration• Rate of flow declines as the rate of Rate of flow declines as the rate of

head loss builds (influent- or effluent-head loss builds (influent- or effluent-controlled).controlled).

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Periodic Summary:Periodic Summary:

Drinking water treatment typically Drinking water treatment typically include clarification, filtration and include clarification, filtration and disinfection.disinfection.

Drinking water treatment should make Drinking water treatment should make water both potable and palatable.water both potable and palatable.

Wastewater and drinking water Wastewater and drinking water treatment processes are similar in treatment processes are similar in several ways.several ways.

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VII. Water TreatmentVII. Water Treatment

B3. Disinfection of drinking B3. Disinfection of drinking waterwater

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Objectives - students Objectives - students should:should:

Define and give examples of Define and give examples of types of disinfection techniques types of disinfection techniques for drinking water.for drinking water.

Distinguish between physical and Distinguish between physical and chemical disinfection techniques.chemical disinfection techniques.

Evaluate the safety, cost, Evaluate the safety, cost, effectiveness, and popularity of effectiveness, and popularity of various disinfection techniques.various disinfection techniques.

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Types of disinfection:Types of disinfection:

Physical disinfection techniques Physical disinfection techniques include boiling and irradiation with include boiling and irradiation with ultraviolet light.ultraviolet light.

Chemical disinfection techniques Chemical disinfection techniques include adding chlorine, bromine, include adding chlorine, bromine, iodine, and ozone to water.iodine, and ozone to water.

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Physical disinfection Physical disinfection (boiling):(boiling):

Boiling kills vegetative bacterial cells, Boiling kills vegetative bacterial cells, but spores, viruses, and some protozoa but spores, viruses, and some protozoa may survive long periods of boiling.may survive long periods of boiling.

Boiling may also volatilize VOC’s.Boiling may also volatilize VOC’s. Boiling is an effective method for small Boiling is an effective method for small

batches of water during water batches of water during water emergencies.emergencies.

Boiling is prohibitively Boiling is prohibitively expensiveexpensive for for large quantities of water.large quantities of water.

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Physical disinfection Physical disinfection (UV radiation):(UV radiation):

Ultraviolet radiation is an effective and Ultraviolet radiation is an effective and relatively safe disinfection method, but relatively safe disinfection method, but is relatively expensive and not widely is relatively expensive and not widely used.used.

UV light disrupts DNA of microbial UV light disrupts DNA of microbial cells, preventing reproduction.cells, preventing reproduction.

Specific wavelengths, intensities, Specific wavelengths, intensities, distances, flow rates, and retention distances, flow rates, and retention times are required. times are required.

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Chemical disinfection:Chemical disinfection:

Chemicals added to water for Chemicals added to water for disinfection include chlorine, disinfection include chlorine, bromine, and iodine.bromine, and iodine.

Bromine is not recommended for Bromine is not recommended for drinking water disinfection, but drinking water disinfection, but may be used for pool water.may be used for pool water.

Iodine is sometimes used for Iodine is sometimes used for drinking water disinfection, but drinking water disinfection, but causes a bad aftertaste.causes a bad aftertaste.

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Chlorine disinfection:Chlorine disinfection:

Chlorination is a cheap, effective, Chlorination is a cheap, effective, relatively harmless (and therefore relatively harmless (and therefore most popular) disinfection method.most popular) disinfection method.

Chlorine is added as a gas or Chlorine is added as a gas or hypochlorite solution.hypochlorite solution.

Hypochlorous acid and hypochlorite Hypochlorous acid and hypochlorite ions form in solution, which are strong ions form in solution, which are strong chemical oxidants, and kill microbes.chemical oxidants, and kill microbes.

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Chlorine disinfection Chlorine disinfection (cont.):(cont.):

Combined chlorine is the proportion Combined chlorine is the proportion that combines with organic matter.that combines with organic matter.

Free chlorine is the amount that Free chlorine is the amount that remainsremains to kill microbes in the to kill microbes in the distribution system (0.5 ppm, 10 min.)distribution system (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.

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Disinfection By-Products Disinfection By-Products (DBPs)(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 (CHIIodoform (CHI33), chlorobromoform (CHBrCl), chlorobromoform (CHBrCl22), ), Bromochloroform (CHBrBromochloroform (CHBr22Cl), Bromoidodform Cl), Bromoidodform (CHBr(CHBr22I), etc.I), etc.

THMs are carcinogenicTHMs are carcinogenic Choroamine disinfection reduce THMs Choroamine disinfection reduce THMs

production due to preferential reaction of production due to preferential reaction of chlorine with ammoniachlorine with ammonia

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Ozonation:Ozonation:

Ozone (OOzone (O33) is an effective, relatively ) is an effective, relatively harmless disinfection method, but harmless disinfection method, but is expensive (and therefore less is expensive (and therefore less popular than chlorine).popular than chlorine).

Ozone is a strong oxidant, that Ozone is a strong oxidant, that produces hydroxyl free radicals that produces hydroxyl free radicals that react with organic and inorganic react with organic and inorganic molecules in water to kill microbes.molecules in water to kill microbes.

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Summary:Summary:

Disinfection is the destruction of Disinfection is the destruction of microorganisms in drinking water microorganisms in drinking water to safe levels.to safe levels.

Disinfection techniques include Disinfection techniques include physical (boiling, ultraviolet light) physical (boiling, ultraviolet light) and chemical methods (chlorine, and chemical methods (chlorine, bromine, iodine, and ozone).bromine, iodine, and ozone).