Download - Water Treatment Processes Water Treatment Plant Operation

Water Treatment Water Treatment ProcessesProcesses

Water Treatment Plant Water Treatment Plant

OperationOperation

Florida Rural Water Association Water Treatment Plant Operation

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Water Treatment Water Treatment ProcessesProcesses

Section 1: Water Treatment ConcernsSection 1: Water Treatment Concerns Section 2: Well ConsiderationsSection 2: Well Considerations Section 3: Conventional Water System Section 3: Conventional Water System

ProcessesProcesses Section 4: Disinfection By-Product ControlSection 4: Disinfection By-Product Control Section 5: Corrosion ControlSection 5: Corrosion Control Section 6: Demineralization ProcessesSection 6: Demineralization Processes Section 7: Coagulation Process ControlSection 7: Coagulation Process Control Section 8: Water SofteningSection 8: Water Softening


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Section 1:Section 1:Water Treatment Water Treatment

ConcernsConcerns

Microbial Contamination ConcernsMicrobial Contamination Concerns Barriers to Contaminants Reaching Barriers to Contaminants Reaching

the Publicthe Public Where Contamination Comes FromWhere Contamination Comes From Bacterial Indicators and PathogensBacterial Indicators and Pathogens Primary Standards Primary Standards Secondary StandardsSecondary Standards


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Microbial Contamination is Microbial Contamination is Primary Concern of Water Primary Concern of Water

OperatorsOperatorsColiform bacteriaColiform bacteria Common in the environment and are generally not harmful but their presence Common in the environment and are generally not harmful but their presence

in drinking water indicates that the water may be contaminated and can cause in drinking water indicates that the water may be contaminated and can cause disease.disease.

Fecal Coliform and E coliFecal Coliform and E coli Bacteria whose presence indicates that the water may be contaminated with Bacteria whose presence indicates that the water may be contaminated with

human or animal wastes. Microbes in these wastes can cause short-term human or animal wastes. Microbes in these wastes can cause short-term

effects, such as diarrhea, cramps, nausea, headaches, or other symptoms.effects, such as diarrhea, cramps, nausea, headaches, or other symptoms. TurbidityTurbidity Has no health effects. However, turbidity can interfere with disinfection and Has no health effects. However, turbidity can interfere with disinfection and

provide a medium for organisms that include bacteria, viruses, and parasites provide a medium for organisms that include bacteria, viruses, and parasites that can cause symptoms such as nausea, cramps, diarrhea, and associated that can cause symptoms such as nausea, cramps, diarrhea, and associated headaches.headaches.


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Multiple Barrier ApproachMultiple Barrier Approach

Source: Selection and Protection

Treatment: Methods and Efficiencies

Distribution: Maintenance and Monitoring


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Where Contamination Where Contamination Comes FromComes From

ConditionCondition Test For:Test For:Reoccurring Gastro-illness*Reoccurring Gastro-illness* Coliform in Drinking WaterColiform in Drinking Water

Pipeline FailurePipeline Failure pH, Lead, and CopperpH, Lead, and Copper

Nearby AgricultureNearby Agriculture Nitrates, Pesticides and ColiformNitrates, Pesticides and Coliform

Nearby MiningNearby Mining Metals and pHMetals and pH

Nearby LandfillNearby Landfill VOCs, TDS, Chlorides, & SulfateVOCs, TDS, Chlorides, & Sulfate

Nearby Fueling Nearby Fueling VOCsVOCs

Bad Taste/OdorsBad Taste/Odors Hydrogen Sulfide and IronHydrogen Sulfide and Iron

Stains Clothes/PlumbingStains Clothes/Plumbing Hydrogen Sulfide and IronHydrogen Sulfide and Iron

Scaly ResidueScaly Residue HardnessHardness* Multiple Sources, ie. runoff, septic tanks, CAFOs


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Microbial Contaminants Microbial Contaminants found in Surface Water or found in Surface Water or

UDI SourcesUDI Sources

Cryptosporidium and GiardiaCryptosporidium and Giardia Parasites that enters lakes and rivers through Parasites that enters lakes and rivers through

sewage and animal waste. These typically sewage and animal waste. These typically cause mild gastrointestinal diseases. cause mild gastrointestinal diseases. However, the disease can be severe or fatal However, the disease can be severe or fatal for people with severely weakened immune for people with severely weakened immune systems. EPA and CDC have prepared systems. EPA and CDC have prepared advice for those with severely compromised advice for those with severely compromised immune systems who are concerned about immune systems who are concerned about these organisms.these organisms.


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Some Facts About BacteriaSome Facts About Bacteria Bacteria are widely distributed on earthBacteria are widely distributed on earth They have been found 4 miles above earth and They have been found 4 miles above earth and

3 miles below sea sediments.3 miles below sea sediments. One gram of fertile soil contains up to One gram of fertile soil contains up to

100,000,000 bacteria.100,000,000 bacteria. Bacteria are inconceivably small and measured Bacteria are inconceivably small and measured

in microns. One micron is equal to 1/1,000,000 in microns. One micron is equal to 1/1,000,000 of a meter.of a meter.

During the rapid growth phase bacteria During the rapid growth phase bacteria undergo fission (cell division) about every 20 undergo fission (cell division) about every 20 to 30 minutes.to 30 minutes.

One bacterial cell after 36 hrs of uncontrolled One bacterial cell after 36 hrs of uncontrolled growth, could fill approximately 200 dump growth, could fill approximately 200 dump truckstrucks..

Bacteria and PathogenicBacteria and PathogenicIndicators in Water Indicators in Water TreatmentTreatment

Photo: CDC. Photo: CDC. E. coliE. coli 0157:H7 0157:H711 of 140 cause gastrointestinal disease11 of 140 cause gastrointestinal disease

Total Total

ColiformColiformFermentFerment

Lactose @ Lactose @ 3535OOCC

IncludeInclude

SpeciesSpecies

of of

GeneraGenera

CitrobacterCitrobacter

EnterobacterEnterobacter

KlebsiellaKlebsiella

E. ColiE. Coli

Fecal Fecal ColiformColiform

Grow at 44Grow at 44OOCC

Produce Produce EnzymeEnzyme

E. ColiE. Coli More Specific More Specific Indicator of Indicator of ContaminationContamination

HPCHPC < 500 < 500 colonies/mlcolonies/ml


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Identifying Source of Identifying Source of ContaminantsContaminants


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Primary or Inorganic Primary or Inorganic ContaminantsContaminants

Mineral-Based Compounds Mineral-Based Compounds

These include metals, nitrates, and asbestos. These include metals, nitrates, and asbestos. These contaminants are naturally-occurring in These contaminants are naturally-occurring in some water, but can also get into water some water, but can also get into water through farming, chemical manufacturing, and through farming, chemical manufacturing, and other human activities. other human activities. Potential health Potential health effects include learning disorders, effects include learning disorders, kidney and liver damage. kidney and liver damage. EPA has set EPA has set legal limits on 15 inorganic contaminants.legal limits on 15 inorganic contaminants.


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Primary Standards and their Primary Standards and their Maximum Contaminant Levels (MCLs) Maximum Contaminant Levels (MCLs)

ContaminantContaminant MCL (mg/l)MCL (mg/l)ArsenicArsenic 0.010 0.010AsbestosAsbestos 7 (MFL) 7 (MFL)FluorideFluoride 4.0 4.0MercuryMercury 0.002 0.002NickelNickel 0.1 0.1NitrateNitrate 1010NitriteNitrite 1 1Total Nitrate+Nitrite 10Total Nitrate+Nitrite 10SodiumSodium 160 160


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Disinfectants and Disinfectants and Disinfection By-ProductsDisinfection By-Products

Disinfectants are water additives that Disinfectants are water additives that are used to control microbesare used to control microbes

Disinfection By-products are created Disinfection By-products are created when chlorine is added in the presence when chlorine is added in the presence of naturally occurring low levels of of naturally occurring low levels of organic materials found in drinking organic materials found in drinking waterwater

Both are regulated because of health Both are regulated because of health concernsconcerns


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Secondary Standards and Secondary Standards and ConcernsConcerns

These compounds cause aesthetic These compounds cause aesthetic concerns such as taste, odor and concerns such as taste, odor and color. color.

EPA recommends MCL limits EPA recommends MCL limits Some states such as Florida have Some states such as Florida have

set regulatory limits on these set regulatory limits on these contaminantscontaminants


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Secondary StandardSecondary StandardMaximum Contaminant LevelsMaximum Contaminant Levels

Contaminant MCL (mg/l)

Chloride 250Sulfate 250 TDS 500 Copper 1.0Fluoride 2.0Iron 0.30 Manganese 0.05Silver 0.1pH (MRCL) 6.5 to 8.5Color (MCRL) 15 cfu


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Protecting Well by Protecting Well by GroutingGrouting

Prevent movement of Prevent movement of water between water between aquifer formationsaquifer formations

Preserve quality of Preserve quality of producing zonesproducing zones

Preserve YieldPreserve Yield Prevent water Prevent water

intrusion from surfaceintrusion from surface Protect Casing Protect Casing

against Corrosion!against Corrosion!Pressure Testing of Grout Seal @

~10 psi for 1 hr. Should be Performed.


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Section 2Section 2Well ConsiderationsWell Considerations

Floridan AquiferFloridan Aquifer Well ContaminantsWell Contaminants Preventing Contamination at the Preventing Contamination at the

Well HeadWell Head


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Floridian Aquifer Across Florida


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Well Source Water Well Source Water ParametersParameters

Quality and Quantity Dictates Depth of Quality and Quantity Dictates Depth of WellWell

TDSTDS Total HardnessTotal Hardness Total Fe and MnTotal Fe and Mn Chlorides & Chlorides &

SulfatesSulfates Total AlkalinityTotal Alkalinity NitrateNitrate

pHpH CorrosivityCorrosivity COCO22

HH22SS FluorideFluoride

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Preventing Contamination Preventing Contamination at the Well Head at the Well Head

## ObservationObservation Likely PathwayLikely Pathway

11 Septic tanks, Septic tanks, broken storm or broken storm or san. pipes, pondssan. pipes, ponds

Through Surface StrataThrough Surface Strata

22 Drainage up-hillDrainage up-hill Surface water runoffSurface water runoff

33 Well subject to Well subject to floodingflooding

Surface water transport Surface water transport of contaminantsof contaminants

44 Casing Casing terminationtermination

Must be 1’ and above Must be 1’ and above 100 yr flood plane100 yr flood plane


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(continued)(continued)## ObservationObservation Likely PathwayLikely Pathway

55 Area around well Area around well is wetis wet

Corroded Casing PipeCorroded Casing Pipe

66 Possible Possible Abandoned wells Abandoned wells in areain area

Surface water intrusion Surface water intrusion from contaminated from contaminated sourcesource

77 Sanitary Sanitary condition condition unacceptableunacceptable

Contaminated water Contaminated water intrusionintrusion

88 Cracking in Well Cracking in Well SlabSlab



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99 Evidence of Evidence of Algae or Mold on Algae or Mold on SlabSlab

Birds and insects Birds and insects attracted by moist attracted by moist conditionsconditions

1010 Poor DrainagePoor Drainage Surface water intrusion Surface water intrusion from contaminated from contaminated sourcesource

1111 Seal water Seal water Draining into well Draining into well headhead

Contaminated water Contaminated water entering borehole entering borehole

1212 Well Seal Well Seal damageddamaged



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1313 Fittings pointing Fittings pointing upwardupward

Contaminated Water Contaminated Water intrusion into casingintrusion into casing

1414 Well vent not Well vent not properly installedproperly installed

Contaminated Water Contaminated Water intrusion into casingintrusion into casing

1515 Check Valve Check Valve absent or not absent or not workingworking

Contaminated water Contaminated water back-flowing into casing back-flowing into casing

1616 Cavitation or Cavitation or water hammerwater hammer

Ck. Valve damage & Ck. Valve damage & water back-flowing into water back-flowing into casingcasing


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1717 Well Site Security Well Site Security CompromisedCompromised

Contaminated Water Contaminated Water from undesirable from undesirable activitiesactivities

1818 Livestock or wild Livestock or wild animals close byanimals close by

Animal source of Animal source of ContaminationContamination

1919 Surface water Surface water evidence IDevidence ID

Indicator organisms, Indicator organisms, color, temp and TOC color, temp and TOC contributingcontributing

2020 Several wells Several wells availableavailable

One well is more likely One well is more likely to contribute than othersto contribute than others


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2121 Intermittent Well Intermittent Well OperationOperation

Contaminated occurring Contaminated occurring from long-term from long-term biological activitybiological activity

2222 Wet or extreme Wet or extreme weather eventsweather events

Contamination from run-Contamination from run-off or from higher off or from higher pumping levels.pumping levels.


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Section 3:Section 3:Conventional Water System Conventional Water System ProcessesProcesses

TOC in Source WaterTOC in Source Water Disinfection and Uses of ChlorineDisinfection and Uses of Chlorine Aeration and Aerator TypesAeration and Aerator Types Iron and Hydrogen Sulfide ControlIron and Hydrogen Sulfide Control FiltrationFiltration SedimentationSedimentation


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Organic Carbon (TOC) in Organic Carbon (TOC) in Natural Waters mg/lNatural Waters mg/l

.1 .2 .5 1.0 2 5 10 20 50 100 200 500 1000

Sea Water

Ground Water

Surface Water Swamp

Wastewater

Wastewater Effluent

Mean Surface Water 3.5


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Disinfection with Chlorine

The primary methods of disinfection is the use of The primary methods of disinfection is the use of chlorine gas, chloramines, ozone, ultraviolet light, chlorine gas, chloramines, ozone, ultraviolet light, chlorine dioxide, and hypochlorite.chlorine dioxide, and hypochlorite.

Generally Chlorine will be used by small systems and Generally Chlorine will be used by small systems and may be applied as a gas, solid or liquid.may be applied as a gas, solid or liquid.

The most common chlorine application is sodium The most common chlorine application is sodium hypochlorite or bleach.hypochlorite or bleach.

Primary Disinfectants are used to inactivate microbes Primary Disinfectants are used to inactivate microbes and Secondary Disinfectants are used to provide for a and Secondary Disinfectants are used to provide for a residual chlorine concentration that prevents microbial residual chlorine concentration that prevents microbial regrowthregrowth.


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Reactions of Chlorine with Reactions of Chlorine with Water ConstituentsWater Constituents

Reducing Compound (inorganics)Reducing Compound (inorganics) Production of ChloraminesProduction of Chloramines Production ChlororganicsProduction Chlororganics Combined ChlorineCombined Chlorine Breakpoint ChlorinationBreakpoint Chlorination Free Chlorine ResidualFree Chlorine Residual


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Breakpoint Chlorination Curve

Chloromine

Add NH3

DISINFECTION BYPRODUCTS REMAIN

Fe

Mn

H2SDichloromine

0

0.2

0

0.6


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Other Chlorine UsesOther Chlorine Uses

Chlorine is often used as an oxidant to remove Chlorine is often used as an oxidant to remove inorganic impurities such as iron and hydrogen sulfideinorganic impurities such as iron and hydrogen sulfide

When used in this manner particulate matter is formed When used in this manner particulate matter is formed that often must be removed.that often must be removed.

Chlorine is also used to prevent the growth of algae on Chlorine is also used to prevent the growth of algae on tank walls and other surfaces exposed to sunlight and tank walls and other surfaces exposed to sunlight and to prevent bacteria from growing inside filters and to prevent bacteria from growing inside filters and tankstanks

Chlorine has been used to remove color, taste and Chlorine has been used to remove color, taste and odors but will produce disinfection by-products which odors but will produce disinfection by-products which are regulatedare regulated


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AerationAeration

Aeration is generally used in small Aeration is generally used in small systems to remove naturally occurring systems to remove naturally occurring dissolved gasses from the water such as dissolved gasses from the water such as CO2 and H2S.CO2 and H2S.

Aeration may also be used to oxidize Aeration may also be used to oxidize iron which then drops out as precipitate iron which then drops out as precipitate and must be filtered.and must be filtered.

Special aerators called Packed Towers Special aerators called Packed Towers are sometimes used to remove VOCsare sometimes used to remove VOCs


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Cascade Tray AeratorCascade Tray Aerator

Even distribution of Even distribution of water over top traywater over top tray

Loading Rates of 1 to Loading Rates of 1 to 5 GPM for each sft. 5 GPM for each sft. of Tray area.of Tray area.

Trays ½” openings Trays ½” openings perforated bottomsperforated bottoms

Protection from Protection from insects with 24 mesh insects with 24 mesh screenscreen


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Forced Draft Aeration Forced Draft Aeration SystemSystem

Includes Includes weatherproof blower weatherproof blower in housingin housing

Counter air through Counter air through aerator columnaerator column

Includes 24 mesh Includes 24 mesh screened downturned screened downturned inlet/outletinlet/outlet

Discharges over 5 or Discharges over 5 or more traysmore trays


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Packed Tower Odor Packed Tower Odor Removal SystemRemoval System

Uses Henry’s Law Uses Henry’s Law constants for mass constants for mass transfertransfer

Usually requires pilot Usually requires pilot testingtesting

Used to Remove VOCs Used to Remove VOCs below MCLbelow MCL

Col to Packing >7:1 ratioCol to Packing >7:1 ratio Air to water at pk >25:1Air to water at pk >25:1 with max 80:1with max 80:1 Susceptible to Fouling Susceptible to Fouling

from CaCO3 > 40 PPMfrom CaCO3 > 40 PPM


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Iron Problems - Most Prevalent in Unconfined, Iron Problems - Most Prevalent in Unconfined, Surficial, and Biscayne AquifersSurficial, and Biscayne Aquifers

Iron dissolved by Iron dissolved by reaction with COreaction with CO22

Iron from well sources Iron from well sources will be in a dissolved will be in a dissolved statestate

When exposed to OWhen exposed to O22

precipitants form precipitants form Visible as red and brown Visible as red and brown

color color Will stain fixtures and Will stain fixtures and

clothesclothes Imparts taste and odorImparts taste and odor


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Iron, Turbidity/TOC Iron, Turbidity/TOC RelationshipsRelationships


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Dissolved Iron ProblemsDissolved Iron Problems

Soluble iron passing into the water Soluble iron passing into the water distribution systemdistribution system will encourage will encourage the growth of iron bacteriathe growth of iron bacteria

Precipitates will form in the Precipitates will form in the distribution systemdistribution system

Iron particles will stain clothes and Iron particles will stain clothes and fixtures (Red Water Complaints)fixtures (Red Water Complaints)


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Treatment of Dissolved Treatment of Dissolved IronIron

Type of TreatmentType of Treatment Removal ConsiderationsRemoval Considerations

Oxidation w/ Oxidation w/ Chlorine Chlorine

Max. 0.1 mg/l w/o Max. 0.1 mg/l w/o filtrationfiltration

Greensand FilterGreensand Filter 0 – 10 mg/l w/ pH > 6.80 – 10 mg/l w/ pH > 6.8

Ion Exchange Ion Exchange SoftenerSoftener

0 – 10 mg/l0 – 10 mg/l

Phosphate AdditionPhosphate Addition 0 – 2 mg/l0 – 2 mg/l


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FeFe++++ AerationAeration

Plot of Plot of pH vs. Time pH vs. Time

for Iron for Iron Removal at Removal at

90%90%EfficiencyEfficiency

(min 30 (min 30 minutesminutes

detention)detention)


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Filtration Requirements forFiltration Requirements forIron and ManganeseIron and Manganese

Requires bé DEP at > 1.0 mg/l FeRequires bé DEP at > 1.0 mg/l Fe Turbidity must be no more than 2 Turbidity must be no more than 2

NTUs above Source WaterNTUs above Source Water Oxidized particles must generally Oxidized particles must generally

be removed be removed Anthracite filters are frequently Anthracite filters are frequently

employed with higher iron contentemployed with higher iron content


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Hydrogen Sulfide Removal Hydrogen Sulfide Removal Techniques (DEP)Techniques (DEP)

Sulfide Sulfide (mg/l)(mg/l)

Recommended Recommended Treatment ProcessTreatment Process

Achievable Range Achievable Range of Removal of Removal

100%100%

< 0.3

Direct ChlorinationDirect Chlorination

> 0.3 Direct ChlorinationDirect Chlorination(requires filtration)(requires filtration)

100%

0.3 to 0.6 Conventional AerationConventional Aeration 50%50%

0.6 to 3.0 Forced Draft AerationForced Draft Aeration 90%90%

> 3.0 Packed Tower AerationPacked Tower Aeration > 90%> 90%


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Hydrogen Sulfide Removal Hydrogen Sulfide Removal DynamicsDynamics

SolubleGas


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ClarificationClarification

Clarifiers are often used in water Clarifiers are often used in water treatment to allow particles to settle treatment to allow particles to settle prior to filtration.prior to filtration.

Special clarifiers called “Upflow Special clarifiers called “Upflow Clarifiers” are used in surface water Clarifiers” are used in surface water treatment plants that used coagulants treatment plants that used coagulants and in softening plants that use lime. and in softening plants that use lime. These types of clarifiers perform several These types of clarifiers perform several treatment processes in one tanktreatment processes in one tank


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Causes of Poor Clarifier Causes of Poor Clarifier PerformancePerformance

If Surface water plant flocculators If Surface water plant flocculators are not adjusted for rate of floware not adjusted for rate of flow

Sludge removal is not routineSludge removal is not routine There is no test to control sludge There is no test to control sludge

quantitiesquantities Settled water turbidities are not measured

or are not measured routinely (e.g., minimum of once per shift)


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FiltrationFiltration Filters are primarily used to remove particulate matter Filters are primarily used to remove particulate matter

and turbidity from the water.and turbidity from the water. The primary types of filters used in water treatment are The primary types of filters used in water treatment are

Rapid Sand or gravity and Pressure Filters Rapid Sand or gravity and Pressure Filters Special Membrane Filters are used for Particulate and Special Membrane Filters are used for Particulate and

Microbial removal.Microbial removal. Special Filters employ Resins and Media such as Special Filters employ Resins and Media such as

greensand and are used to remove select contaminants greensand and are used to remove select contaminants such as iron and manganese. Activated carbon filters are such as iron and manganese. Activated carbon filters are

used to remove organic compoundsused to remove organic compounds..


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Filter ApplicationsNanofiltration


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Media Configurations forMedia Configurations forGravity FiltersGravity Filters

Single media Single media (sand)(sand)

Dual Media (sand Dual Media (sand and anthracite)and anthracite)

Mixed or multi-Mixed or multi-media (sand, media (sand, anthracite and anthracite and garnet)garnet)

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Characteristics of Various Characteristics of Various FiltersFilters

FilterFilter MediaMedia Sz Sz (mm)(mm)

SpeSpecc

GraGravv

DepthDepth(in)(in)

FlowFlow Flow Flow gpm/sfgpm/sf

Slow SandSlow Sand Fine SandFine Sand 0.20.2 2.62.6 36 – 4836 – 48 GravityGravity .05 - .03.05 - .03

Rapid SandRapid Sand Course SandCourse Sand 0.35 – 0.35 – 1.01.0

2.62.6 24 – 3624 – 36 GravityGravity 2 – 42 – 4

Dual MediaDual Media Anthracite Anthracite SandSand

0.9 – 1.20.9 – 1.2

0,4 – 0,4 – 0,550,55

1.4 – 1.4 – 1.61.6

2.62.6

18 – 2418 – 24

6 – 106 – 10GravityGravity 4 – 54 – 5

Mixed Mixed MediaMedia

AnthraciteAnthracite

Sand, GarnetSand, Garnet0.9 – 1.20.9 – 1.2

0,4 – 0,4 – 0,550,55

0.20.2

1.4 – 1.4 – 1.61.6

2.62.6

4.24.2

16.516.5

99

4.54.5

GravityGravity 55

Diatom. EarthDiatom. Earth DiatomaceouDiatomaceouss

0.005 to0.005 to

0,1250,1251/16 to 1/81/16 to 1/8 PressurPressur

e or e or VacuumVacuum

0.5 – 50.5 – 5

PressurePressure All MediaAll Media ApplicatioApplicationn

PressurPressuree

2 – 42 – 4


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Calculating Filter Flow Calculating Filter Flow RateRate

1.1. Determine Surface Area of Filter Determine Surface Area of Filter 2.2. Measure Filter Rise with stopwatch and tape Measure Filter Rise with stopwatch and tape

measure (often meters are out of calibration)measure (often meters are out of calibration)

Example: 150 sft surface area, 10.7” rise in Example: 150 sft surface area, 10.7” rise in 20 seconds20 seconds (10.7 in / 12 in/ft) x 150 sft x 7.48 gal/cft = 1000 gal.(10.7 in / 12 in/ft) x 150 sft x 7.48 gal/cft = 1000 gal. (20 seconds / 60 min ) = 0.333 min(20 seconds / 60 min ) = 0.333 min

Flow Rate = Flow Rate = 1000 gal / 0.333 min1000 gal / 0.333 min = 20 gpm / sft = 20 gpm / sft 150 sf150 sf


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Causes of PoorCauses of PoorFilter PerformanceFilter Performance

Filter Problems: operational, mechanical Filter Problems: operational, mechanical equipment failure, media failureequipment failure, media failure

Turbidity Errors: calibration, air bubbles, Turbidity Errors: calibration, air bubbles, debrisdebris

Chemical Feed Failures: coagulant, Chemical Feed Failures: coagulant, coagulant aid, filter aidcoagulant aid, filter aid

Poor Water Quality: increased turbidity, Poor Water Quality: increased turbidity, algaealgae

Operating Plant intermittently Operating Plant intermittently exceeding peak loading capacityexceeding peak loading capacity


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Common Filter Operation Common Filter Operation DeficienciesDeficiencies

Filters are started dirty (i.e., without

backwashing

Increases in plant flow rate made with no

consideration of filtered water quality

Filter to waste capability is not being

used or not monitored if utilized

Filters removed from service without

reducing plant flow, resulting in overload

Operations staff backwash the filters

without regard for filter effluent turbidity

Backwash rate too low for longer period or

stopped early to conserve water

No testing of filters resulting in media loss, underdrain or support

gravel damage

Significant build up of mudballs in filter media

Individual filtered water quality is different and

quality is not monitored

Performance following backwash is not

monitored or recorded.

There are no records available which

document performance

Calibration procedures are not practiced


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Filter Integrity TestingFilter Integrity Testing Evaluates filter media, support gravel Evaluates filter media, support gravel

and underdrainsand underdrains Check for filter depth, surface cracking, Check for filter depth, surface cracking,

mudball and segregationmudball and segregation Media is checked by excavationMedia is checked by excavation Steel rod is used to probe support gravel Steel rod is used to probe support gravel

location and uniformity (should vary < location and uniformity (should vary < 2”)2”)

Observe clearwell for evidence of mediaObserve clearwell for evidence of media Check for uneven flow splitting to filtersCheck for uneven flow splitting to filters


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Backwash ParametersBackwash Parameters

Typically at about 24 hour intervalsTypically at about 24 hour intervals Rate: 15 gpm/sft – 20 gpm/sftRate: 15 gpm/sft – 20 gpm/sft Expand at min. 25%Expand at min. 25% Backwashing Duration: 5 - 10 min.Backwashing Duration: 5 - 10 min. Filter to waste for 3 - 5 min.Filter to waste for 3 - 5 min. Water used for backwashing: 2% - 4% per filter ofWater used for backwashing: 2% - 4% per filter of

total water producedtotal water produced


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15 to 20 gpm/sft

Min. Expansion 25%

Sand Filter ~40%

Multimedia ~25%

Deep Bed ~50%


56

Determining Backwash Determining Backwash Expansion in PlantExpansion in Plant

Can be made with tin can lid


57

Visual Identification of Visual Identification of Filter ProblemsFilter Problems

Mudballs – Formed by chemical deposits of Mudballs – Formed by chemical deposits of solids during backwashing (leads to coating solids during backwashing (leads to coating of media surfaces)of media surfaces)

Surface Cracking – Caused by compressible Surface Cracking – Caused by compressible matter around media at surfacematter around media at surface

Media Boils – Caused by too rapid of Media Boils – Caused by too rapid of backwash and displaces gravel support backwash and displaces gravel support belowbelow

Air Binding – Caused by excessive headloss Air Binding – Caused by excessive headloss (infrequent backwashing) allowing air to (infrequent backwashing) allowing air to enter media from belowenter media from below


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Section 4 Section 4 Disinfection By-Product Disinfection By-Product ControlControl

Disinfection By-Product FormationDisinfection By-Product Formation Factors Affecting By-Product Factors Affecting By-Product

FormationFormation Locating THM and HAA5 AreasLocating THM and HAA5 Areas Formation of THMs and HAA5sFormation of THMs and HAA5s Controlling Disinfection By-ProductsControlling Disinfection By-Products Importance of Water AgeImportance of Water Age Flushing Methods and BenefitsFlushing Methods and Benefits


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Disinfection By-Product (DBP) Disinfection By-Product (DBP) FormationFormation

Disinfection Byproducts (DBP) are produced by the Disinfection Byproducts (DBP) are produced by the reaction of free chlorine with organic material found in reaction of free chlorine with organic material found in natural waters.natural waters.

The amount of organic materials in a natural water called The amount of organic materials in a natural water called NOM can be approximated by the amount of Total NOM can be approximated by the amount of Total Organic Carbon (TOC) present in the water source.Organic Carbon (TOC) present in the water source.

NOM consists of various chemical compounds NOM consists of various chemical compounds containing carbon, originating from decayed natural containing carbon, originating from decayed natural vegetative matter found in water. vegetative matter found in water.


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Factors Affecting Disinfection Factors Affecting Disinfection By-Product ProductionBy-Product Production

Turbidity and the type of NOM presentTurbidity and the type of NOM present Concentration of Chlorine addedConcentration of Chlorine added pH of waterpH of water Bromide Ion ConcentrationBromide Ion Concentration TemperatureTemperature Contact TimeContact Time


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Locating TTHM AreasLocating TTHM Areas

High Water Age High Water Age

Storage Tanks do not fluctuateStorage Tanks do not fluctuate

No / Few Customer AreasNo / Few Customer Areas

Stagnant AreasStagnant Areas

Dead EndsDead Ends

Bad PipeBad Pipe

Regrowth AreasRegrowth Areas

Pipe Tuberculation with Bacterial Growth producing Organic Precursors


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Locating HAA5 AreasLocating HAA5 Areas

Low Demand Areas

Toward Middle System Areas w/ Stagnant / Low

Water Age

Areas with No / Little Regrowth

– Eliminate Biodegradation Locations

– Free Chlorine Residuals < 0.2 mg/L

– HPC Data

No Dead Ends

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Formation of DBP in a Water Formation of DBP in a Water SystemSystem

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Disinfectant and DBP Production in a Disinfectant and DBP Production in a Typical Water SystemTypical Water System


65

DBP Reduction Techniques in a DBP Reduction Techniques in a Water Distribution SystemWater Distribution System

Reducing detention time in storage Reducing detention time in storage tanks, tanks,

Ensuring turnover in distribution system Ensuring turnover in distribution system Flushing dead-end lines.Flushing dead-end lines.


66

Typical Distribution System Typical Distribution System Water Age (Days) in PipelinesWater Age (Days) in Pipelines

PopulationPopulation Miles of WMMiles of WM Water AgeWater Age

> 750,000> 750,000 > 1,000> 1,000 1 – 7 days1 – 7 days

< 100,000< 100,000 < 400< 400 > 16 days> 16 days

< 25,000< 25,000 < 100< 100 12 – 24 12 – 24 days days

AWWA: Water Age for Ave and Dead End Conditions

67

There are Two Types of Flushing There are Two Types of Flushing Used by Water Distribution Used by Water Distribution

SystemsSystems

Unidirectional Flushing

> 2.5 fps velocity that removes solid deposits and biofilm from

pipelines

Conventional Flushing

< 2.5 fps velocity that reduces water age, raises disinfectant residual removes coloration

&


68

How Often to FlushHow Often to Flush

• Dead-end mains at least monthly Dead-end mains at least monthly • Other flushing points at least twice annually Other flushing points at least twice annually

(DEP requires quarterly flushing) (DEP requires quarterly flushing) • At intervals necessary to maintain consistent At intervals necessary to maintain consistent

water quality throughout the distribution system water quality throughout the distribution system • Often enough to maintain adequate disinfection Often enough to maintain adequate disinfection

residuals throughout the distribution system residuals throughout the distribution system • Whenever Customer complaints of bad taste, Whenever Customer complaints of bad taste,

odor, clarity or turbidity are received (DEP odor, clarity or turbidity are received (DEP requirement)requirement)


69

Flushing Benefits Flushing Benefits SummarizedSummarized

• Restores disinfectant residual Restores disinfectant residual • Maintains or improves water quality Maintains or improves water quality

a. Reduces bacterial growth a. Reduces bacterial growth b. Reduces customer complaints b. Reduces customer complaints

• Restores flow and pressure in the distribution system Restores flow and pressure in the distribution system a. Reduces sediment a. Reduces sediment b. Reduces corrosion and tuberculation in mains b. Reduces corrosion and tuberculation in mains

• Reduces DBP problems and lowers disinfection costs Reduces DBP problems and lowers disinfection costs • Reduces pipeline maintenance costs Reduces pipeline maintenance costs • Increases life expectancy of the distribution system Increases life expectancy of the distribution system • Typically results in a fire hydrant maintenance programTypically results in a fire hydrant maintenance program


70

Section 5 Section 5 Corrosion ControlCorrosion Control

Corrosion Control MethodsCorrosion Control Methods Factors Affecting CorrosionFactors Affecting Corrosion Corrosion Tuberculation ExampleCorrosion Tuberculation Example pH and Alkalinity RelationshipspH and Alkalinity Relationships Langerlier IndexLangerlier Index Troubleshooting Corrosion ComplaintsTroubleshooting Corrosion Complaints Basics of SequesteringBasics of Sequestering


71

Corrosion and Chemical Corrosion and Chemical ActivityActivity

Most all forms of corrosion are chemical Most all forms of corrosion are chemical reactions (erosion is the exception) reactions (erosion is the exception) that require three things:that require three things:

1.1. A carrier such as Water that allows the movement of A carrier such as Water that allows the movement of positively charged ions (from Anode+ to Cathode-)positively charged ions (from Anode+ to Cathode-)

2.2. A condition (water metal contact) that allows metals to A condition (water metal contact) that allows metals to disassociate (ionize) and allows electrons to flowdisassociate (ionize) and allows electrons to flow

3.3. An imbalance that favors the transport of metals or An imbalance that favors the transport of metals or ions to achieve a chemical balance in a water solution.ions to achieve a chemical balance in a water solution.


72

Corrosion Control MethodsCorrosion Control Methods

Corrosion Control is employed in water treatment Corrosion Control is employed in water treatment to protect pipeline materials, appurtenances and to protect pipeline materials, appurtenances and fittings from leaching problematic (iron) and/or fittings from leaching problematic (iron) and/or dangerous inorganic chemicals (lead and copper).dangerous inorganic chemicals (lead and copper).

Three types of treatment are generally used: 1.) Three types of treatment are generally used: 1.) Chemical Adjustment, Water Treatment and Chemical Adjustment, Water Treatment and SequesteringSequestering

Protection Measures in water system include the Protection Measures in water system include the use of sacrificial metals and electronic cathodic use of sacrificial metals and electronic cathodic protection.protection.


73

Factors Affecting Factors Affecting CorrosionCorrosion

Water’s pHsWater’s pHs Water alkalinityWater alkalinity Solids contentSolids content TemperatureTemperature Materials Used for pipes and other Materials Used for pipes and other

fittings.fittings.

74

Cathodic Action Resulting inCathodic Action Resulting inTuberculation in Water PipelinesTuberculation in Water Pipelines

Inside Pipe Wall

1.5”


75

Effects of pH on the Rate of Corrosion of Iron in Water


76

Relationships between Relationships between Alkalinity, pH Alkalinity, pH

A Water can be Corrosive or Depositing

based upon it’s pH and

Alkalinity.


77

Affects of Raising or Lowering Affects of Raising or Lowering Alkalinity and COAlkalinity and CO22 by Chemical by Chemical

AdditionAddition


78

Determining pH of WaterDetermining pH of Water

pH = log pH = log {{2.2 x 102.2 x 1066 X X (Alkalinity in mg/l as (Alkalinity in mg/l as

CaCO3CaCO3))} }

(CO(CO

22 in mg/l) in mg/l)

Measured Alkalinity Measured Alkalinity

60 mg/l as CaCO60 mg/l as CaCO33

Measured COMeasured CO22

= 7.4 mg/l= 7.4 mg/l

pH = log pH = log {{2.2 x 102.2 x 1066 X 60/7.4 X 60/7.4 } } = 7.25= 7.25Approximate pH between 7.0 to 8.0


79

Use of the Langerlier Index Use of the Langerlier Index for Determining Water for Determining Water

StabilityStability

Every water has a particular pH value Every water has a particular pH value where the water will neither deposit where the water will neither deposit scale nor cause corrosion. scale nor cause corrosion.

A stable condition is termed saturation. A stable condition is termed saturation. Saturation (pHs), varies depending on Saturation (pHs), varies depending on

calcium hardness, alkalinity, TDS, and calcium hardness, alkalinity, TDS, and temperature. temperature.

The Langerlier Index = pH – pHsThe Langerlier Index = pH – pHs Corrosive < LI = 0 > Scale FormingCorrosive < LI = 0 > Scale Forming


80

Recommended Treatment for Recommended Treatment for Corrosive and Scaling Water based Corrosive and Scaling Water based

on LIon LI

Saturation IndexSaturation Index DescriptionDescription General RecommendationGeneral Recommendation

- 5 Severe Corrosion Treatment Recommended

- 4 Severe Corrosion Treatment Recommended

- 3 Moderate Corrosion Treatment Recommended

- 2 Moderate Corrosion Treatment May Be Needed

-1 Mild Corrosion Treatment May Be Needed

-0.5 None- Mild Corrosion Probably No Treatment

0 Near Balanced No Treatment

0.5 Some Faint Coating Probably No Treatment

1 Mild Scale Coating Treatment May Be Needed

2 Mild to Moderate Coatings Treatment May Be Needed

3 Moderate Scale Forming Treatment Advisable

4 Severe Scale Forming Treatment Advisable


81

Troubleshooting Customer Troubleshooting Customer Complaints caused by CorrosionComplaints caused by Corrosion

Water CharacteristicWater Characteristic Likely Cause Likely Cause

Red/reddish-brown WaterRed/reddish-brown Water Distribution Pipe Corrosion Distribution Pipe Corrosion

Blueish Stains on fixturesBlueish Stains on fixtures Copper Line Corrosion Copper Line Corrosion

Black WaterBlack Water Sulfide Corrosion of Iron Sulfide Corrosion of Iron

Foul Tastes and OdorsFoul Tastes and Odors By-Products of Bacteria By-Products of Bacteria

Loss of PressureLoss of Pressure Tuberculation Tuberculation

Lack of Hot WaterLack of Hot Water Scaling Scaling

Reduced Life of Plumbing Reduced Life of Plumbing Pitting from Corrosion Pitting from Corrosion

Tastes Like Garden HoseTastes Like Garden Hose Backflow From Hose Backflow From Hose


82

Sequestering Action ofSequestering Action ofPoly and Ortho PhosphatesPoly and Ortho Phosphates


83

Polyphosphates for Sequestering Polyphosphates for Sequestering Soluble Iron and Manganese after Soluble Iron and Manganese after

TreatmentTreatment

The Polyphosphate, Hexametaphosphate is The Polyphosphate, Hexametaphosphate is commonly used for Sequestering Soluble Iron commonly used for Sequestering Soluble Iron and Manganeseand Manganese

Sequestering is used when soluble Iron and Sequestering is used when soluble Iron and Manganese exists after treatment; The Agent Manganese exists after treatment; The Agent is added after sedimentationis added after sedimentation

Large doses (>5 mg/l) will soften rust Large doses (>5 mg/l) will soften rust deposits in pipelines which are transported deposits in pipelines which are transported into homesinto homes

Proper dose is to keep soluble iron and/or Proper dose is to keep soluble iron and/or manganese tied up for 4 daysmanganese tied up for 4 days


84

Use of Orthophosphates Use of Orthophosphates for Sequesteringfor Sequestering

Orthophosphate is used to sequester Orthophosphate is used to sequester iron ions at pipe surfacesiron ions at pipe surfaces

The Sequestering forms a protective The Sequestering forms a protective coating that prevents further iron coating that prevents further iron migrationmigration

Ortho/Poly Blends provide both Ortho/Poly Blends provide both sequestering of soluble iron and iron sequestering of soluble iron and iron movement from pipelines under movement from pipelines under corrosive conditionscorrosive conditions


85

Section 6:Section 6:Demineralization Demineralization ProcessesProcesses

Basic Demineralization SystemsBasic Demineralization Systems RO Operating ConsiderationsRO Operating Considerations Pretreatment; Fouling and Scaling Pretreatment; Fouling and Scaling

IssuesIssues Ion Exchange ConsiderationsIon Exchange Considerations Sodium/Calcium ExchangeSodium/Calcium Exchange


86

Ion Exchange, Membrane Ion Exchange, Membrane Filtration and Filtration and ElectrodialysisElectrodialysis

Several special treatment processes are used to Several special treatment processes are used to remove selected mineral contaminants from the remove selected mineral contaminants from the water. These include Ion Exchange, Membrane water. These include Ion Exchange, Membrane Filtration and Electrodialysis. Filtration and Electrodialysis.

These systems remove selected salts such as These systems remove selected salts such as sodium, hardness consisting of Calcium and sodium, hardness consisting of Calcium and Magnesium and removal of selected contaminants Magnesium and removal of selected contaminants such as Nitrate or Arsenicsuch as Nitrate or Arsenic


87

Reverse Osmosis (RO)Reverse Osmosis (RO)Treatment ConsiderationsTreatment Considerations

Used to Remove Highly Used to Remove Highly Concentrated Salts (TDS) Concentrated Salts (TDS)

Operating pressure < 400 psi Operating pressure < 400 psi Salt Rejection Rates of < 95%Salt Rejection Rates of < 95% Turbidity <1 NTUTurbidity <1 NTU Flux Range 15 – 32 GFD (gallons Flux Range 15 – 32 GFD (gallons

Flux per day per sq. ft. membrane Flux per day per sq. ft. membrane surface)surface)


88

Pretreatment Requirements for Reverse Osmosis Systems

Suspended ParticulatesSuspended Particulates

Colloidal materialsColloidal materials

Microbiological MatterMicrobiological Matter

ChlorineChlorine

CarbonatesCarbonates

SulfateSulfate

SilicaSilica

IronIron

Hydrogen SulfideHydrogen Sulfide

Blockage FiltrationBlockage Filtration

Fouling Coagulation/FiltrationFouling Coagulation/Filtration

Fouling ChlorineFouling Chlorine

Failure GAC or DechlorinationFailure GAC or Dechlorination

Scaling pH adjust or SofteningScaling pH adjust or Softening

Scaling Inhibitor or Cation Rem.Scaling Inhibitor or Cation Rem.

Scaling SofteningScaling Softening

Scale/Foul Greensand (no Scale/Foul Greensand (no aeration)aeration)

Scale/Foul Degasification Scale/Foul Degasification


89

Operating ConsiderationsOperating ConsiderationsIon Exchange SofteningIon Exchange Softening

Iron and ManganeseIron and Manganese Corrosiveness of Brine SolutionCorrosiveness of Brine Solution Pump StrainerPump Strainer Fouling of Resin Fouling of Resin


90

Optimal Water Optimal Water Characteristics for Ion Characteristics for Ion

ExchangeExchange

pHpH 6.5 – 9.0 6.5 – 9.0

NONO33 < 5 mg/l< 5 mg/l

SOSO44 < 50 mg/l< 50 mg/l

TDSTDS < 500 mg/l< 500 mg/l

TurbidityTurbidity < 0.3 NTU< 0.3 NTU

Selectivity Considerations

S04-2 > NO3-2 > CO3-2 > NO2-2 > CL-1


91

Sodium Exchange Sodium Exchange MCL Considerations MCL Considerations

Sodium provides Sodium provides 100% exchange100% exchange for Ca for Ca++++ and Mg and Mg++ ++

NaZeolite + CaNaZeolite + Ca++++ --> CaZeolite + Na --> CaZeolite + Na++ and and NaZeolite + MgNaZeolite + Mg++++ --> MgZeolite + Na --> MgZeolite + Na++

For every grain (17.1 grains = 1 mg/l) of hardness removed For every grain (17.1 grains = 1 mg/l) of hardness removed from water, about 8.6 mg/1 of sodium is added.from water, about 8.6 mg/1 of sodium is added.

Sodium MCL = 160 mg/l - Initial Na water concentration + NaOClSodium MCL = 160 mg/l - Initial Na water concentration + NaOCl 5 grains needed for corrosion control (86 mg/l) thus: 5 grains needed for corrosion control (86 mg/l) thus:

source water hardness limit ~ source water hardness limit ~ 350 mg/l hardness350 mg/l hardness (~20 grains) (~20 grains)

ie. ie. 100% x 5 grains100% x 5 grains, or 15 grains removed x 8 = 134 mg/l Na or 15 grains removed x 8 = 134 mg/l Na 20 grains 20 grains Provides Provides 134 mg/l Na134 mg/l Na and and 5 grains or 86 mg/l Hardness5 grains or 86 mg/l Hardness


92

Section 7Section 7Coagulation Processes Coagulation Processes ControlControl

Metal Charges and Electron AttractionMetal Charges and Electron Attraction Elemental Weights and Chemical Elemental Weights and Chemical

FormulasFormulas Particle Chemistry and Colloidal Particle Chemistry and Colloidal

ParticlesParticles The Floc Building ProcessThe Floc Building Process Optimizing the Coagulation ProcessOptimizing the Coagulation Process Use of a Jar TestUse of a Jar Test

93

Periodic Table of the Periodic Table of the ElementsElements

Valances are shown at the top of the Periodic Table, Valances are shown at the top of the Periodic Table,

F is one electron short and Mg has two extra electronsF is one electron short and Mg has two extra electrons

94

The Periodic ChartThe Periodic Chartalso Provide the Atomic Weight also Provide the Atomic Weight

of an Elementof an Element

8

O Oxygen

15.99

Atomic Number

Symbol

Name

Atomic Weight

Includes Isotopes

Use 16


95

Solids and Colloidal Solids and Colloidal MaterialMaterial

Suspended Suspended SolidsSolids

Suspended in the Water and can Suspended in the Water and can be Removed by Conventional be Removed by Conventional FiltrationFiltration

ColloidsColloids Finely Charged Particles that do Finely Charged Particles that do not Dissolvednot Dissolved

Turbidity Turbidity The Cloudy Appearance of Water The Cloudy Appearance of Water caused by Suspended Matter and caused by Suspended Matter and ColloidsColloids

Zeta Zeta PotentialPotential

Electrical Charge of a suspended Electrical Charge of a suspended particleparticle


96

Primary CoagulantsPrimary Coagulants

Primary coagulants are lime, Primary coagulants are lime, aluminum sulfate (alum), ferrous aluminum sulfate (alum), ferrous sulfate, ferric sulfate and ferric sulfate, ferric sulfate and ferric chloride.chloride.

These inorganic salts will react These inorganic salts will react with the alkalinity in the water to with the alkalinity in the water to form insoluble flocs which will trap form insoluble flocs which will trap the suspended matter in them.the suspended matter in them.


97

Removal of Colloidal Removal of Colloidal Particles by Coagulation & Particles by Coagulation &

FlocculationFlocculation

Floc Building Process : Floc Building Process :

Neutralization of repulsive chargesNeutralization of repulsive charges Precipitation with sticky flocsPrecipitation with sticky flocs Bridging of suspended matterBridging of suspended matter Providing “agglomeration sites” for Providing “agglomeration sites” for

larger floclarger floc Weighting down of floc particlesWeighting down of floc particles


98

Polymers and Ionic Polymers and Ionic ChargesCharges

Cationic + Cationic + *Anionic - *Anionic - NonionicNonionic

Bridging Action of Cationic Bridging Action of Cationic Polymer with Colloidal Polymer with Colloidal

ParticlesParticles

* Used with Metal Coagulants in water treatment


99

Factors Affecting the Factors Affecting the Coagulation ProcessCoagulation Process

pH (pH Range: Al, 5 – 7 ; Fe, 5 – 8)pH (pH Range: Al, 5 – 7 ; Fe, 5 – 8) Alkalinity of water (> 30 PPM residual)Alkalinity of water (> 30 PPM residual) Concentration of Salts (affect efficiency)Concentration of Salts (affect efficiency) Turbidity (constituents and concentration)Turbidity (constituents and concentration) Type of Coagulant used (Al and Fe salts)Type of Coagulant used (Al and Fe salts) Temperature (colder requires more mixing)Temperature (colder requires more mixing) Adequacy of mixing (dispersion of chemical)Adequacy of mixing (dispersion of chemical)


100

Jar Test Plot for Low Jar Test Plot for Low Alkalinity or Low Turbidity Alkalinity or Low Turbidity

WaterWater

Alum initially reacts Alum initially reacts with low alkalinitywith low alkalinity

With Ferric Chloride With Ferric Chloride requires chemical requires chemical to reach optimal pH to reach optimal pH before reactingbefore reacting

Adding too much Adding too much coagulant coagulant increases turbidity increases turbidity


101

Section 8:Section 8:Hardness and Water Hardness and Water SofteningSoftening

Hardness Removal by SofteningHardness Removal by Softening Treatment Methods Used to Remove Treatment Methods Used to Remove

HardnessHardness Alkalinity DefinitionsAlkalinity Definitions Alkalinity/Acidity RelationshipsAlkalinity/Acidity Relationships pH and Lime TreatmentpH and Lime Treatment Removal of Color and OrganicsRemoval of Color and Organics Importance of RecarbonationImportance of Recarbonation


102

Water Hardness Water Hardness Hardness in Water causes scaling, causes fibers Hardness in Water causes scaling, causes fibers

in clothes to become brittle and increases the in clothes to become brittle and increases the amount of soap that must be used for washingamount of soap that must be used for washing

Hardness in water is caused by the water’s Hardness in water is caused by the water’s Calcium and Magnesium ContentCalcium and Magnesium Content

Water is considered hard when it has a Water is considered hard when it has a hardness concentration of > 100 mg/l expressed hardness concentration of > 100 mg/l expressed as calcium carbonate equivalentas calcium carbonate equivalent

Water that hardness < 100 mg/l expressed as Water that hardness < 100 mg/l expressed as CaCO3 is considered softCaCO3 is considered soft

Hardness can either be removed by water Hardness can either be removed by water treatment or sequestered using phosphatestreatment or sequestered using phosphates


103

Methods of Removing Methods of Removing HardnessHardness

Treatment MethodTreatment Method Hardness Levels Hardness Levels RetainedRetained

Lime SofteningLime Softening

(Chemical (Chemical Precipitation)Precipitation)

Solubility Level of Solubility Level of about 35 mg/l about 35 mg/l (CaCO3)

RO (Nanofiltration)RO (Nanofiltration)

(Membrane (Membrane Filtration)Filtration)

85 – 90% removal85 – 90% removal

Ion ExchangeIon Exchange

(Chemical (Chemical Exchange)Exchange)

Basically ZeroBasically Zero

Water must be Water must be blendedblended


104

Alkalinity DefinitionsAlkalinity Definitions

The capacity of water to neutralize acids.The capacity of water to neutralize acids. The measure of how much acid must be added to a The measure of how much acid must be added to a

liquid to lower the pH to 4.5liquid to lower the pH to 4.5 It is caused by the water’s content of carbonate, It is caused by the water’s content of carbonate,

bicarbonate, hydroxide, and occasionally borate, bicarbonate, hydroxide, and occasionally borate, silicate, and phosphate.silicate, and phosphate.

In natural waters, Alkalinity = Bicarbonate In natural waters, Alkalinity = Bicarbonate Hardness = Total Carbonate HardnessHardness = Total Carbonate Hardness


105

Relationships among pH, Relationships among pH, Alkalinity and IndicatorsAlkalinity and Indicators

Bicarbonate and CarbonateBicarbonate

CO2

P=0

100%0%

pH

T=0

100%

T Alkalinity

P Alkalinity

9.4 10.610.2

Carbonate and Hydroxide

CaCO3 Mg(OH)2


106

Types of Alkalinity that Types of Alkalinity that can be Present at pH can be Present at pH

ValuesValues Below 4.5 only COBelow 4.5 only CO22 present, no Alkalinity present, no Alkalinity Between 4.5 to 8.3 only Bicarbonate presentBetween 4.5 to 8.3 only Bicarbonate present Between 8.3 to 10.2 Bicarbonate & Carbonate. Between 8.3 to 10.2 Bicarbonate & Carbonate. Between 10.2 to 11.3 Carbonate & HydroxideBetween 10.2 to 11.3 Carbonate & Hydroxide

At 9.4 Calcium Carbonate becomes insoluble At 9.4 Calcium Carbonate becomes insoluble and precipitatesand precipitates

At 10.6 Magnesium Hydroxide becomes At 10.6 Magnesium Hydroxide becomes insoluble and precipitatesinsoluble and precipitates


107

Removal of Organics Removal of Organics by Lime Softening by Lime Softening

PrecipitationPrecipitation

Calcium Carbonate 10% to 30% of Calcium Carbonate 10% to 30% of Color, TOC & DBP Color, TOC & DBP

Magnesium Hydroxide 30% to 60% of Magnesium Hydroxide 30% to 60% of TOC & DBP andTOC & DBP and 80% of Color80% of ColorAddition of Alum/Ferric +5% to +15% of Addition of Alum/Ferric +5% to +15% of Color, TOC & DBP Color, TOC & DBP Sequential Treatment Additional RemovalSequential Treatment Additional Removal Color, TOC and DBPColor, TOC and DBP


108

Recarbonation in Lime Recarbonation in Lime SofteningSoftening

Because water has unused lime (calcium Because water has unused lime (calcium hydroxide) and magnesium hydroxide in hydroxide) and magnesium hydroxide in solution at high pH (pH 11), these must be solution at high pH (pH 11), these must be converted to a stable forms.converted to a stable forms.

COCO22 is added to reduce Ca(OH) is added to reduce Ca(OH)22 to CaCO to CaCO33 which precipitates at about pH 10; additional which precipitates at about pH 10; additional COCO22 is added to convert Mg(OH) is added to convert Mg(OH)2 2 to soluble to soluble Mg(HCOMg(HCO33))2 2 which occurs at a pH of 8.4.which occurs at a pH of 8.4.

Reaction must be completed before filtration Reaction must be completed before filtration so that calcium carbonate will not precipitate so that calcium carbonate will not precipitate in the filters or carry into distribution system.in the filters or carry into distribution system.


109

Water Treatment Water Treatment SummarySummary

Effective Water Treatment Requires the Effective Water Treatment Requires the application of accepted principlesapplication of accepted principles

Most Process Problems in Water Treatment Most Process Problems in Water Treatment are the result of failure to recognize the are the result of failure to recognize the symptoms that result from improper symptoms that result from improper application or adherence to these factorsapplication or adherence to these factors

Most treatment plant problems can be Most treatment plant problems can be resolved by application of the techniques resolved by application of the techniques presented presented

Download - Water Treatment Processes Water Treatment Plant Operation

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