Waste water

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Waste water

  1. 1. Wastewater – Its Journey to Treatment and Return to the Environment ESI
  2. 2. Where does it all go! Where does the water from the washer go? When you flush the toilet where does the contents go? By gravity flow, the waste is on its way to your local wastewater treatment plant!
  3. 3. Why treat wastewater? • Causes a demand for dissolved oxygen (lower DO levels of streams) • Adds nutrients (nitrate and phosphate) to cause excessive growth • Increases suspended solids or sediments in streams (turbidity increase)
  4. 4. Western Branch WWTP Blue Plains WWTP Mattawoman WWTP Sewagesheds Piscataway WWTP Parkway WWTP Marlboro Meadows WWTP Bowie WWTP approximate boundaries - an area where sewage is collected and delivered to a WWPT
  5. 5. Where do you locate the WWTP in the watershed? A B C D Consider the four possible sites.
  6. 6. 0 5 10 15 20 25 30 35 Parkway BowieW estern Branch Piscataw ay M arlboro M eadows M attaw om an WWTP milliongallon/day Capacity Average Flow The volume of wastewater PGC 1992 Comprehensive Ten Year Water and Sewerage Plan
  7. 7. Levels of Treatment Primary – removal by physical separation of grit and large objects (material to landfill for disposal) Secondary – aerobic microbiological process (sludge) organic matter + O2  CO2 + NH3 + H2O NH3  NO3 - - lowers suspended solids content (into sludge) aquatic nutrient Mostly dead microbes
  8. 8. Aeration and rapid mixing Settling collects sludge on bottom Secondary process ir iffuser Fromprimaryprocess Totertiaryprocess
  9. 9. Levels of Treatment continued Tertiary (advanced) – anaerobic microbiological process with a different microbe where O2 is toxic (more sludge) NO3 -  N2 (escapes to atmosphere) – PO4 -3 if not removed in sludge in secondary process PO4 -3 + Al+3  AlPO4 (s) (into sludge) - aeration to strip N2 and re-oxygenate (add DO)
  10. 10. Slow mixing to keep suspended and O2 out Settling collects sludge on bottom Tertiary process Fromsecondaryprocess Effluent add methanol as food source
  11. 11. When the treatment is done… • Effluent back to stream after – a final carbon filtration and – chlorination/dechlorination • Sludge – very nutrient rich – applied directly to land as fertilizer – incinerated (good fuel after drying) – composted (Compro® from WSSC) Note – Leafgro® is composted leaves and grass from MES

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