Water Purification and Wastewater Treatment

Water Purification and Water Purification and Wastewater TreatmentWastewater Treatment

Water PurificationWater Purification

• ScreeningScreening

• Chlorination, fluoridationChlorination, fluoridation

• Chemical applicationChemical application– Aluminum sulfate (“alum”)Aluminum sulfate (“alum”)• CoagulationCoagulation

– Activated charcoalActivated charcoal• Removes objectionable tastes and odorsRemoves objectionable tastes and odors


• Mixing BasinsMixing Basins– Alum chemically reacts to form “floc”Alum chemically reacts to form “floc”• Gelatinous particles Gelatinous particles

– Water in mixing basins is stirredWater in mixing basins is stirred• Promotes collisions betwen floc particlesPromotes collisions betwen floc particles

– Floc particles grow in sizeFloc particles grow in size• Entrain bacteria and sedimentEntrain bacteria and sediment


• Settling BasinsSettling Basins– Flocculated material settles out and is Flocculated material settles out and is

piped to wastewater treatment plantpiped to wastewater treatment plant

• Sand FiltersSand Filters– Hydrated lime added to minimize Hydrated lime added to minimize

corrosioncorrosion– Polishing operationPolishing operation


• Temporary storage in clear wellsTemporary storage in clear wells

• Filtered-water reservoirFiltered-water reservoir– ChlorinationChlorination– Caustic soda to minimize corrosiveness Caustic soda to minimize corrosiveness

of polished waterof polished water– Gravity flow to pumping stationsGravity flow to pumping stations

Wastewater TreatmentWastewater Treatment

• Septic Tanks Septic Tanks – Bacteria in sewage degrade organic Bacteria in sewage degrade organic

mattermatter– Tank buried in ground to treat sewage Tank buried in ground to treat sewage

from an individual homefrom an individual home– Wastewater flows into tankWastewater flows into tank

Septic Tank SystemSeptic Tank System


• Septic Tanks Septic Tanks – Solid material (“sludge”) settles to Solid material (“sludge”) settles to

bottom of tankbottom of tank– Cleaner water flows out of tank into Cleaner water flows out of tank into

ground through subsurface drainsground through subsurface drains


• Lagoons (Stabilization Ponds)Lagoons (Stabilization Ponds)– 3-5’ deep3-5’ deep– Sunlight, algae, oxygen interact to clean Sunlight, algae, oxygen interact to clean

wastewaterwastewater


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• CollectionCollection• TreatmentTreatment


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• CollectionCollection

– SewersSewers• CombinedCombined• SeparateSeparate

Stormwater and Sanitary Sewer SystemStormwater and Sanitary Sewer System



– Combined SewersCombined Sewers• Carry stormwater and wastewaterCarry stormwater and wastewater

– Separated SewersSeparated Sewers• Sanitary SewersSanitary Sewers• Storm SewersStorm Sewers



– Household sewerHousehold sewer– Lateral sewerLateral sewer– Main sewersMain sewers– InterceptorsInterceptors– Wastewater treatment plantWastewater treatment plant



– High rainfall eventsHigh rainfall events• Some wastewater may be diverted to Some wastewater may be diverted to

receiving streamsreceiving streams


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• TreatmentTreatment

– FunctionFunction• To speed up natural processes by which To speed up natural processes by which

water purifies itselfwater purifies itself• DO is the key!DO is the key!


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• TreatmentTreatment

– ProcessesProcesses• Primary Primary • SecondarySecondary• AdvancedAdvanced

The Wastewater Treatment ProcessThe Wastewater Treatment Process


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• Primary TreatmentPrimary Treatment

– Mechanical processMechanical process• ScreeningScreening• GrindingGrinding• Grit Chamber (heavy particles - “grit”)Grit Chamber (heavy particles - “grit”)• Sedimentation Tank (suspended solids - Sedimentation Tank (suspended solids -

“sludge”) “sludge”) • Chlorination of effluentChlorination of effluent


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• Secondary TreatmentSecondary Treatment

– Biological processBiological process• Uses bacteria to removed ODW and lower Uses bacteria to removed ODW and lower

BODBOD– TypesTypes

• Trickling FilterTrickling Filter• Activated SludgeActivated Sludge


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• Secondary Treatment With Trickling Filters Secondary Treatment With Trickling Filters

– Effluent leaves sedimentation tank and flows Effluent leaves sedimentation tank and flows through through trickling filterstrickling filters• Bed of stones 3-10’ deep through which Bed of stones 3-10’ deep through which

sewage passessewage passes• Bacteria gather on stones and multiply, Bacteria gather on stones and multiply,

consuming ODWconsuming ODW• Cleaner water trickles through pipes at Cleaner water trickles through pipes at

bottom of filter for additional treatmentbottom of filter for additional treatment


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• Secondary Treatment With Activated Secondary Treatment With Activated

SludgeSludge– Effluent leaves sedimentation tank and is Effluent leaves sedimentation tank and is

pumped to an pumped to an aeration tank aeration tank – Effluent is mixed with air and sludge loaded with Effluent is mixed with air and sludge loaded with

bacteria (bacteria (“activated sludge”“activated sludge”))– Sludge contacts with raw sewage, and bacteria in Sludge contacts with raw sewage, and bacteria in

the sludge then decompose the raw sewage, the sludge then decompose the raw sewage, lowering ODW and BODlowering ODW and BOD


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses

• Secondary Treatment With Activated SludgeSecondary Treatment With Activated Sludge– Activated sludge-sewage mixture is called Activated sludge-sewage mixture is called mixed mixed

liquorliquor– Mixed liquor leaves aeration tank and flows to Mixed liquor leaves aeration tank and flows to

another sedimentation tank where suspended another sedimentation tank where suspended solids settle out for reuse as activated sludgesolids settle out for reuse as activated sludge

– Effluent is chlorinatedEffluent is chlorinated– Activated sludge in sedimentation tank is reusedActivated sludge in sedimentation tank is reused


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• Advanced (Tertiary) Wastewater TreatmentAdvanced (Tertiary) Wastewater Treatment

– Physical and chemical processes that specific Physical and chemical processes that specific pollutants left in wastewater after primary and pollutants left in wastewater after primary and secondary treatmentsecondary treatment

– Extremely costly! Extremely costly! • It cost twice as much to build a tertiary It cost twice as much to build a tertiary

treatment plant compared to a secondary treatment plant compared to a secondary treatment planttreatment plant


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• Advanced (Tertiary) Wastewater TreatmentAdvanced (Tertiary) Wastewater Treatment

– ProcessesProcesses• Bleaching to remove colorationBleaching to remove coloration• Disinfection to kill pathogensDisinfection to kill pathogens• Coagulation-sedimentation with alumCoagulation-sedimentation with alum• Adsorption using activated charcoalAdsorption using activated charcoal• Electrodialysis for salt removalElectrodialysis for salt removal


• Conventional Sewage TreatmentConventional Sewage Treatment– ProcessesProcesses• Sludge DisposalSludge Disposal

– LandfillsLandfills– IncinerationIncineration– Land applicationLand application– Anaerobic digestion Anaerobic digestion


• Water Quality ProtectionWater Quality Protection– Federal LawsFederal Laws• Clean Water Act (1977)Clean Water Act (1977)• Water Quality Act (1987)Water Quality Act (1987)• U.S. Safe Drinking Water Act (1974)U.S. Safe Drinking Water Act (1974)


• Water Quality ProtectionWater Quality Protection– Clean Water ActClean Water Act• To restore and/or maintain the chemical, To restore and/or maintain the chemical,

physical, and biological integrity of the physical, and biological integrity of the nation’s surface watersnation’s surface waters


• Water Quality ProtectionWater Quality Protection– Safe Drinking Water ActSafe Drinking Water Act• Required USEPA to establish drinking water Required USEPA to establish drinking water

standards (“Maximum Contaminant Levels”) standards (“Maximum Contaminant Levels”) for any pollutant that MAY have adverse for any pollutant that MAY have adverse effects on human healtheffects on human health

• No MCLs established for some SOCs, No MCLs established for some SOCs, radioactive materials, toxic metals, and radioactive materials, toxic metals, and ptahogensptahogens


• Water Quality ProtectionWater Quality Protection– Natural Resources Defense Council Natural Resources Defense Council

StudyStudy• Drinking water of > 50 million Americans Drinking water of > 50 million Americans

exceeds one or more MCL standardsexceeds one or more MCL standards

• Most people have not been notified when Most people have not been notified when their drinking water was contaminatedtheir drinking water was contaminated

• Contaminated drinking water is responsible Contaminated drinking water is responsible for > 7 million ilnesses and 1200 deaths per for > 7 million ilnesses and 1200 deaths per yearyear


• U.S. Water Quality FactsU.S. Water Quality Facts– 44% of lakes, 37% rivers, 32% estuaries 44% of lakes, 37% rivers, 32% estuaries

still unsafe for fishing, swimming, other still unsafe for fishing, swimming, other recreational usesrecreational uses

Documents

Water Purification and Wastewater Treatment