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Fundamentals of Wastewater Treatment

Fundamentals of Wastewater Treatment. Activated sludge processes Fixed film and suspended processes Aerobic/anoxic/anaerobic processes modifications. Nutrient removal nitrification / denitrification, phosphorous removal Water reuse and reclamation membrane bioreactors Disinfection

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Fundamentals of Wastewater Treatment

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  1. 1 Fundamentals of Wastewater Treatment

  2. 2 Activated sludge processes Fixed film and suspended processes Aerobic/anoxic/anaerobic processes modifications. Nutrient removal nitrification / denitrification, phosphorous removal Water reuse and reclamation membrane bioreactors Disinfection Satellite and On-site Wastewater Treatment Wastewater Treatment

  3. 3 Bacteriological, Vibrio Cholerae, Campylobacter, Salmonella , Shigella, Viruses Hepatitis A, Norovirus Protozoan Giardia, Cryptosporidium, Entamoeba Biological oxygen demand Organic matter causes algae to thrive and deplete dissolved oxygen Nutrient removal to prevent eutrophication Nitrogen and phosphorus from waste, and agriculture Wastewater contaminants

  4. 4 What does wastewater look like? Source: Wastewater Engineering, Metcalf and Eddy- medium strength WW

  5. 5 Routine bacterial testing consists of measuring indicator organisms • Testing for pathogens directly is expensive and hazardous • Indicators from the family Enterobacteriacae are used (E. Coli, Citrobacter,Enterobacter, Klebsiella) • Grow bacteria on a specified medai and count the number of colonies after incubation • Other assays are used and are approved by the US EPA (Colilert shown)

  6. 6 Fixed film process Screens Primary settling Grit removal Digester Sludge drying Initial steps in satellite and centralized wastewater treatment Suspended growth process

  7. 7 Biofilm Waste Water Facultative/Anaerobic Bed Media Aerobic ~1 mm 100µm Fixed film biological processes Treated Water

  8. 8 Rotating biological contactor(40% submerged rotates at 1-1.5 rpm) Fixed film biological processes Trickling filter Uses biofilm to treat water to remove BOD

  9. 9 Trickling filter effectiveness BOD5 removal rates for trickling filters Source: Environmental Engineers Handbook, 1997.

  10. 10 Waste Water Activated Sludge Anoxic Aerobic Coagulation Clarifier sludge Treated Water Return activated sludge Suspended growth biological processes Anoxic – no dissolved oxygen

  11. 11 Aerobic Conditions Anaerobic/Aerobic Conditions Aerobic Conditions Anoxic Conditions BOD + O2 P Organic N NO3 CO2 + increased cell mass NH4 increased cell mass Alum N2 NO2 inorganic sludge organic sludge NO3 BOD and nutrient (nitrogen and phosphorous) removal

  12. 12 Suspended growth activated sludge processes requires energy • Use forced air suspension of biological sludge to reduce BOD • Largest expense for this process is the electrical energy required

  13. 13 Activated sludge process stages Aerobic Basin Anoxic Basin Sedimentation Final Clarification

  14. 14 Anaerobic sludge digestion reduces solids - makes methane Anaerobic sludge digestors produce methane (65% CH4 - 35% CO2) On-site electricity is produced with the methane 50% of plant power (2.2MW)

  15. 15 Liquid process train Sedimentation C6H14 Biomass + CO2 NH3+ NO2 Norg NH3+ Mixing Aeration NO2N2 Solids Handling Sedimentation

  16. 16 Modified Ludzack-Ettinger (MLE Process) A2O Bardenpho Exemplary process stages RAS = Return Activated Sludge WAS = Waste Activated Sludge

  17. 17 Solids handling involves anaerobic conditions PNM Diesel Generators Anaerobic Fermentation (30 days) C6H14 + H2O CH4 + CO2 6.6 MW Biosolids Disposal or Reuse (150 t/day) Aeration Blowers Centrifuges

  18. 18 A Typical Process CO2 H2S N2 HOCl- SO2 Sewers River H2O+C+N+S Settling & Aeration H2O Heat Microbes CO2 O2 (Biosolids) NH3+ Power Fermentation Composting CH4 CO2 Humus

  19. 19 Water reuse often uses membrane bioreactor with submerged membranes Conventional activated sludge plant MBR membrane cassette • Uses submerged hollow fiber membranes • High Solids Retention Time membrane bioreactor

  20. 20 Screens Anoxic Aerobic Submerged Membrane Membrane bioreactors offer small size, high rate of reaction for satellite WW

  21. 21 Membrane separation spectrum Source: Zenon Membranes

  22. 22 Screen before membrane bio reactor

  23. 23 Kubota MBR pilot plant

  24. 24 Raw feed and MBR product

  25. 25 Reverse osmosis after MBR makes water suitable for groundwater recharge RO treated water is better than most surface water sources

  26. 26 Hyperion Wastewater Plant Los Angeles 450 mgd 10% of discharge from this plant is sent to microfiltration plant to purify for groundwater injection

  27. 27 West Basin Microfiltration Plant (35 mgd from Hyperion) Submerged microfiltration for treated wastewater effluent

  28. 28 The final step is disinfection and discharge (no residual free chlorine) • Chlorination to kill the remaining pathogens • Cl2HOCl • Dechlorination to remove chlorine • SO2 + HOCl + H2O  HCl + H2SO4 • SO2 + NH2Cl + 2H2O  NH4Cl + H2SO4 • UV radiation reduces chemical needs and chlorinated products

  29. 29 Effect of wastewater on disinfection Source: Wastewater Engineering- Metcalf & Eddy

  30. 30 Satellite and on-site waste disposal • Satellite facilities are mid scale sewage treatment plants that treat waste near the point of generation • Lagoons • Aeration ditches • Trickling filters • Membrane bioreactor • On-site waste disposal is septic tank system with drain field • Provides low cost alternative • Can be very effective • Need little maintenance (but maintenance is important)

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