Wastewater Treatment - PDF

Wastewater Treatment Definition of Wastewater Wastewater is simply that part of the water supply to the community or to the industry which has been used for different purposes and has been mixed with solids either suspended or dissolved. Wastewater Treatment ❖Purpose: To manage water discharge...

Wastewater Treatment Definition of Wastewater Wastewater is simply that part of the water supply to the community or to the industry which has been used for different purposes and has been mixed with solids either suspended or dissolved. Wastewater Treatment ❖Purpose: To manage water discharged from homes, businesses, and industries to reduce the threat of water pollution. Why Treating Wastewater? Domestic and industrial processes use and pollute water => wastewater • Minimize effects of discharge on environment • Remove pollutants for recycling and/or reuse of water Sources of Wastewater: ➢ Domestic or Municipal Wastewater, ➢ Industrial Wastewater, ➢ Infiltration and inflow, ➢ Storm water ❖ Municipal wastewater includes wastewater discharged from: ➢ Residences, ➢ Businesses, ➢ Commercial facilities such as restaurants and shopping centers, ➢ Institutions such as hospitals and schools, ➢ Recreational facilities, ❖ Industrial Wastewater: wastewater discharged from industries. ❖ Infiltration: This includes water that eventually enters the sewer from foundation drains, leaking pipes, submerged manholes and groundwater infiltration, among others. ❖ Storm water: Rainfall runoff and snow melt. Greywater ➢ Greywater is any household wastewater with the exception of wastewater from toilets, which is known as blackwater. ➢ Typically, 50-80% of household wastewater is greywater from kitchen sinks, dishwashers, bathroom sinks, tubs and showers. ➢ Greywater is relatively cleaner than blackwater Use of Greywater With proper treatment of greywater can be put to good use. These uses include: – water for laundry, – toilet flushing, – irrigation of plants. Major Benefits of Greywater Use ➢ Reducing the need for fresh water, ➢ Saving on fresh water use can significantly reduce household water bills, but also has a broader community benefit in reducing demands on public water supply, ➢ Reducing the amount of wastewater entering sewers or on-site treatment systems. Classification of Treatment Methods 1. Physical unit processes screening, mixing, gas transfer, sedimentation, filtration 2. Chemical unit processes chemical precipitation, disinfection 3. Biological unit processes activates sludge process, trickling filter Water Criteria for Treatment Scheme selection ➢ Wastewater quality ➢ Desired treated wastewater quality ➢ Available space for facilities ➢ Capital/operation costs ➢ Waste disposal constraints Wastewater Treatment Levels ❖ Pre-treatment ❖ Preliminary treatment ❖ Primary treatment ❖ Secondary treatment ❖ Tertiary treatment The required level and type of wastewater treatment depends upon the: 1. Influent wastewater characteristics, and 2. the required effluent quality. ❖ Pre-treatment - Occurs in industry prior to discharge - Prevention of toxic chemicals or excess nutrients being discharged wastewater. in Wastewater Treatment Wastewater Treatment ❖Preliminary Treatment - removes large objects and non- degradable materials - protects pumps and equipment from damage - bar screen and grit chamber ➢ Bar Screen - catches large objects that have gotten into sewer system such as bricks, bottles, pieces of wood, etc. ➢ Grit Chamber - removes rocks, gravel, broken glass, etc. ➢ Preliminary Treatment ➢ Measurement and sampling at the inlet structure - a flow meter continuously records the volume of water entering the treatment plant - water samples are taken for determination of suspended solids and B.O.D. ➢ Suspended Solids – the quantity of solid materials floating in the water column ➢ B.O.D. = Biochemical Oxygen Demand - a measure of the amount of oxygen required to aerobically decompose organic matter in the water ➢ Measurements of Suspended Solids and B.O.D. indicate the effectiveness of treatment processes ➢ Both Suspended Solids and B.O.D. decrease as water moves through the wastewater treatment processes ❖ Primary Treatment -- a physical process -- wastewater flow is slowed down and suspended solids settle to the bottom by gravity. -- the material that settles is called sludge or biosolids. ➢ Primary Treatment ➢ Sludge from the primary sedimentation tanks is pumped to the sludge thickener. - more settling occurs to concentrate the sludge prior to disposal. ➢ Primary treatment reduces the suspended solids and the B.O.D. of the wastewater. ➢From the primary treatment tanks water is pumped to the trickling filter for secondary treatment. ➢Secondary treatment will further reduce the suspended solids and B.O.D. of the wastewater. ❖ Secondary Treatment ➢ Secondary treatment is a biological process ➢ Utilizes bacteria and algae to metabolize organic matter in the wastewater ❖ Secondary Treatment ❖Secondary Treatment ➢ the trickling filter does not “filter” the water ➢ water runs over a plastic media and organisms clinging to the media remove organic matter from the water ➢ From secondary treatment on the trickling filter water flows to the final clarifiers for further removal of sludge. ➢ The final clarifiers are another set of primary sedimentation tanks. ➢ From the final clarifiers the water is discharged to a water body. ➢ The final clarifiers remove additional sludge and further reduce suspended solids and B.O.D. ❖ Disposal of Sludge or Biosolids -- the sludge undergoes lime stabilization (pH is raised by addition of lime) to kill potential pathogens -- the stabilized sludge is land applied by injection into agricultural fields SECONDARY TREATMENT – ACTIVATED SLUDGE