Overview of Water TreatmentPhysical, chemical, and biological processes are used for treating water.Unit operation: physical treatment.Unit process: chemical or biological treatment.A series of unit operations and unit processes are selected by the process engineer based on influent characteristics to achieve the desired effluent quality.

Water Treatment ProblemA water treatment plant is to be designed to treatwater with the following characteristics:

High turbidityHigh bacteriological concentrationsNo carbon dioxideMedium colorLow hardness

What is the source of the water?Prepare schematic of treatment train.

Items to ConsiderSource: River variable flow and quality

High turbidity: removed by sedimentation and filtration; suggest presedimentation.

High bacteriological concentrations: removed by disinfection; some microbes removed by coagulation, flocculation and settling; suggest predisinfection.

Carbon dioxide: aerate or add lime if present.

Medium color: ozonation and chlorination will reduce, may be necessary to use activated carbon

Low hardness : would soften if moderately hard.

Screening: unit operation, removes largedebris and tree limbs.Low Lift Pumps: unit operation, providesenergy to lift water up to the treatment plantFlow Meter: unit operation, measures flow.Pre-disinfection: unit process, disinfectant added to lower bacterial and pathogen levels.Plain sedimentation: unit operation, removessuspended solids lowering turbidity.

PlainSedimentationLow Lift Pumps

Mixing: unit operation, dispersion of coagulant.Flocculation: unit process, destabilization ofcolloidal particles and promotion of floc growth.Sedimentation: unit operation, removal of suspended solids, lowers turbidity.Disinfection: unit process, addition of disinfectant to kill pathogens.Coagulant

Filtration: unit operation, removes remaining turbidity and microbial cysts.Disinfection: unit process, disinfectant added to ensure pathogens are destroyed. Clear well provides necessary contact time with disinfectant.High Service Pumps: unit operation, energy provided to pump water throughout distribution system.

Water Treatment ProblemA water treatment plant is to be designed to treatwater with the following characteristics:

Low turbidityLow bacteriological concentrationsModerate carbon dioxideLow colorHigh hardness

What is the source of the water?Prepare schematic of treatment train.

Items to ConsiderSource: Well relatively constant flow and high quality.

Low turbidity: removed by coagulation, flocculation, sedimentation and filtration; may need to add turbidity in the form of clay to provide nucleifor coagulation.

Low bacteriological concentrations: removed by disinfection; some microbes removed by coagulation, flocculation and settling; lime-soda ashtreatment followed by sedimentation and filtration should remove microbes .

Carbon dioxide: aerate or add lime if present.

Low color: ozonation and chlorination will reduce.

High hardness : soften if moderately hard using lime-soda ash; alternativetreatment would be to used membranes rather than conventional treatment.

Wells: unit operation, source of groundwater.Low Lift Pumps: unit operation, providesenergy to lift water up to the treatment plantFlow Meter: unit operation, measures flow.Pre-disinfection: unit process, disinfectant added toreduce pathogen levels and oxidize H2S, Fe & Mg.Tray Aeration: unit operation, removesCO2, H2S, and other gases.

Low Lift Pumps

Mixing: unit operation, dispersion of lime & soda-ash for hardness removal.Flocculation: unit process, destabilization ofcolloidal particles and promotion of floc growth.Sedimentation: unit operation, removal of suspended solids, lowers turbidity.Disinfection: unit process, addition of disinfectant to kill pathogens.Lime & Soda

Filtration: unit operation, removes remaining turbidity and microbial cysts.Disinfection: unit process, disinfectant added to ensure pathogens are destroyed. Clear well provides necessary contact time with disinfectant.High Service Pumps: unit operation, energy provided to pump water throughout distribution system.

Waste water TreatmentAdditional treatment to remove organic matter

Aerobic suspended growth systemsActivated Sludge Process, Oxidation PondsAerobic attached growth systemsTrickling filters, Rotating Biological ContactorsAnaerobic suspended growth systemsAnaerobic Sludge Digestors, Septic TanksAnaerobic attached growth systemsAnaerobic Filters, UASBCombination of aerobic and anaerobic systems