WaterTreatment-UniversityofSouthernMississippi.pptVIP

Water Treatment Water treatment designed to remove microbes, chemicals and pollutants not meant to sterilize Potable water Sewage Treatment Primary treatment Screened and Skimmed Sedimentation Sludge removed Effluent (liquid) moves on to 2nd step Biochemical oxygen demand (BOD) measure of the oxygen required to fully metabolize organic matter in water Directly proportional to amount of waste in water Normally about 10mg/L of oxygen can be dissolved in water Primary treatment removes about 30% of BOD Secondary treatment Predominantly biological; designed to remove organic matter and reduce BOD Sewage undergoes strong aeration Activated sludge Trickle filter Rotating biological contractor Activated sludge system microbes oxidize organic matter into CO2 and water Zooglea form floc Transferred to settling tank; floc settles out Bulking may result in local pollution Trickling filters spray sewage over a bed of rocks or molded plastic Rotating biological contractor Chemical treatment Effluent from secondary treatment is disinfected and discharged Usually involves chlorination Tertiary treatment Sewage treated to a potable level Extremely costly Removes any remaining BOD including most nitrates and phosphates Removes all microbes Sludge treatment Sludge pumped into anaerobic sludge digesters Encourages growth of anaerobic bacteria especially methanogens Decrease organic solids degrades them into methane and CO2 Methane harvested Undigested sludge may be deposited in a landfill or used for soil conditioners Anaerobic Sludge Digester CO2 + 4 H2 ? CH4 + 2 H2O CH3COOH ? CH4 + CO2 Areas with low population density often use septic tanks Sewage flows into a holding tank, particulate matter settles out Effluent flows through a system of perforated pipes into a leaching fields Organics decomposed by soil bacteria * Steps of water treatment: 1. Coagulation: Sedimentation and Flocculation 2. Filtration: Sand or Coal 3. Disinfection: Chlorine; Ozone; UV