《环境化学》课程PPT教学课件讲稿（英文版）Unit 16 Water and Sewage Treatment

Water and Sewage treatment

Water and Sewage Treatment

Objectives of Water Treatment The objectives for water treatment derive from two concerns Human health and welfare The health of aquatic ecosystems

Objectives of Water Treatment • The objectives for water treatment derive from two concerns – Human health and welfare – The health of aquatic ecosystems

Water treatment for domestic and commercial uses Criteria Causing pollutant Corresponding removal measures Free of odor Odorous gases aeration to remove odor gases Free of Particles Addition of fe3t and turbidity Al+ to trap particles OW BOD Organic materials Bacteria metabolism ow nutrient Dissolved N,P Chemical precipitation loading norganIc NH3 stripping Free of disease microorganisms Addition of causing agents disinfectants

Water treatment for domestic and commercial uses Criteria Causing Pollutant Corresponding removal measures Free of odor Odorous gases Aeration to remove odor gases Free of turbidity Particles Addition of Fe3+ and Al3+ to trap particles Low BOD Organic materials Bacteria metabolism Low nutrient loading Dissolved N, P inorganic Chemical precipitation NH3 stripping Free of disease causing agents microorganisms Addition of disinfectants

Primary water treatment Primary treatment: Remove solids by screening and settling The sewage is passed through a screen to remove large pieces of debris(e.g. sticks, stones, rags, and plastic bags) Next, the sewage enters a grit chamber, where the water flow is slowed just enough to allow coarse sand and gravel to settle out on the bottom Water then enters the sedimentation tank its flow rate is further decreased to permit suspended solids to settle out as raw sludge

Primary water treatment • Primary treatment: Remove solids by screening and settling – The sewage is passed through a screen to remove large pieces of debris (e.g. sticks, stones, rags, and plastic bags). – Next, the sewage enters a grit chamber, where the water flow is slowed just enough to allow coarse sand and gravel to settle out on the bottom. – Water then enters the sedimentation tank, its flow rate is further decreased to permit suspended solids to settle out as raw sludge

Primary water treatment( Continued) Ca(OH)2 and al2(SO4)3 are often added to speed up the sedimentation process 3 Cal(oh)2+ A2(S04 )3>2 Al(OH)3+ 3 CaSo4 Al(OH)3 is a gelatinous precipitation that settles out slowly, carrying suspended material and bacteria with it Oily material floats to the surface and is skimmed off. The grit is collected and disposed in landfill The raw sludge: Old way: incinerated, disposed in landfill or dumped at sea New way: composted to produce a nutrient rich bacteria free material for use as fertilizer

Primary water treatment (Continued) • Ca(OH)2 and Al2 (SO4 )3 are often added to speed up the sedimentation process. 3 Ca(OH)2 + Al2(SO4)3 → 2 Al(OH)3 + 3 CaSO4 Al(OH)3 is a gelatinous precipitation that settles out slowly, carrying suspended material and bacteria with it. • Oily material floats to the surface and is skimmed off. • The grit is collected and disposed in landfill. • The raw sludge: – Old way: incinerated, disposed in landfill or dumped at sea. – New way: composted to produce a nutrient rich bacteria￾free material for use as fertilizer

Primary treatment Preliminary treatment Bar screen Raw Debris Gint remos To landfill Primary treatment To remove particulate organic material Water enters at center and flows out aver weir at velocitv. Particulate Rotat organic material settles Constitutes water Fat and oil float to top and are skimmed off Fertilizer

Primary treatment

In older sewage-treatment plants, the water after primary treatment is often chlorinated to kill pathogens and then discharged into a natural waterway. The discharged water at this stage still contains a large amount of oxygen-consuming wastes, which may deplete dissolved oxygen in the water way and cause eutrophication

In older sewage-treatment plants, the water after primary treatment is often chlorinated to kill pathogens and then discharged into a natural waterway. The discharged water at this stage still contains a large amount of oxygen-consuming wastes, which may deplete dissolved oxygen in the water way and cause eutrophication

Secondary treatment Secondary treatment, also called biological treatment: Use bacteria to break down organic compounds to Co2 A mixture of organisms- termed activated sludge- is added to the sewage effluent Air or oxygen is vigorously bubbled through pipes into the effluent The aerobic bacteria digest the organic material and break it down into co2 and water. The bacteria and any remaining undecomposed material are returned to the aeration tank and reused

Secondary treatment • Secondary treatment, also called biological treatment: Use bacteria to break down organic compounds to CO2. – A mixture of organisms – termed activated sludge– is added to the sewage effluent. – Air or oxygen is vigorously bubbled through pipes into the effluent. – The aerobic bacteria digest the organic material and break it down into CO2 and water. – The bacteria and any remaining undecomposed material are returned to the aeration tank and reused

Activated sludge process wastes from prima treatment (CH O)+9-Co (a)+H0+ biomass seCONDArY purine flUent organic N一NH+N SEDIMENT ATION organic P→H2P,HPQ AERATION atr 一【 eturn sludge: excess sludge waste

Activated sludge process

Secondary treatment of municipal wastewater Secondary treatment Organisms settle and become To remove colloidal and next batch of activated sludge dissolved organic material d Activated sludge system Organisms feed on organic material in Aeration tank oxygen-rich environment Activated sludge returns Forced air or oxygen

Secondary treatment of municipal wastewater