Overview of Water Treatment Physical, 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 Problem A water treatment plant is to be designed to treat water with the following characteristics: High turbidity High bacteriological concentrations No carbon dioxide Medium color Low hardness What is the source of the water? Prepare schematic of treatment train.

Items to Consider Source: 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 large debris and tree limbs. Disinfectant Screens Flow Meter Low Lift Pumps Plain Sedimentation Screening: unit operation, removes large debris and tree limbs. Low Lift Pumps: unit operation, provides energy to lift water up to the treatment plant Flow Meter: unit operation, measures flow. Pre-disinfection: unit process, disinfectant added to lower bacterial and pathogen levels. Plain sedimentation: unit operation, removes suspended solids lowering turbidity.

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

Filtration Clear Well Disinfectant High Service Pumps To Distribution System 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 Problem A water treatment plant is to be designed to treat water with the following characteristics: Low turbidity Low bacteriological concentrations Moderate carbon dioxide Low color High hardness What is the source of the water? Prepare schematic of treatment train.

Items to Consider Source: 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 nuclei for coagulation. Low bacteriological concentrations: removed by disinfection; some microbes removed by coagulation, flocculation and settling; lime-soda ash treatment 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; alternative treatment would be to used membranes rather than conventional treatment.

Wells: unit operation, source of groundwater. Low Lift Pumps Aeration Trasy Disinfectant Wells Flow Meter Wells: unit operation, source of groundwater. Low Lift Pumps: unit operation, provides energy to lift water up to the treatment plant Flow Meter: unit operation, measures flow. Pre-disinfection: unit process, disinfectant added to reduce pathogen levels and oxidize H2S, Fe & Mg. Tray Aeration: unit operation, removes CO2, H2S, and other gases.

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

Filtration Clear Well Disinfectant High Service Pumps To Distribution System 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.