2004 Biological Wastewater Treatment Operators School

1. 2004 Biological Wastewater Treatment Operators School Advanced Treatment Systems May 13, 2004 Dean Pond, Black & Veatch

2. Advanced Treatment Systems What are the forms of nitrogen found in wastewater?

3. What are the forms of nitrogen found in wastewater? • TKN = 40% Organic + 60% Free Ammonia Typical concentrations: Ammonia-N = 10-50 mg/L Organic N = 10 – 35 mg/L • No nitrites or nitrates • Forms of nitrogen: Organic N Ammonia Nitrite Nitrate TKN Total N

4. Advanced Treatment Systems Why is it necessary to treat the forms of nitrogen?

5. Why is it necessary to treat the forms of nitrogen? • Improve receiving stream quality • Increase chlorination efficiency • Minimize pH changes in plant • Increase suitability for reuse • Prevent NH4 toxicity • Protect groundwater from nitrate contamination

6. Advanced Treatment Systems What are the effects of N and P in receiving waters?

7. What are the effects of N and P in receiving waters? • Increases aquatic growth (algae) • Increases DO depletion • Causes NH4 toxicity • Causes pH changes

8. Advanced Treatment Systems Why is it sometimes necessary to remove P from municipal wastewater treatment plants?

9. Why is it sometimes necessary to remove P from municipal WWTPs? • Reduce phosphorus, which is a key limiting nutrient in the environment • Improve receiving water quality by: • Reducing aquatic plant growth and DO depletion • Preventing aquatic organism kill • Reduce taste and odor problems in downstream drinking water supplies

10. Advanced Treatment Systems How is P removed by conventional secondary (biological) wastewater treatment plants?

11. How is P removed by conventional secondary (biological) WWTPs? • Biological assimilation BUG = C60H86O23N12P • 0.03 lb P/lb of bug mass • GROW BUGS, WASTE BUGS = REMOVE P

12. Advanced Treatment Systems Where in the treatment plant process flow could chemical precipitants be added?

13. Where in the treatment plant flow could chemical precipitants be added? • At pretreatment • Before primary clarifiers • After aeration basins • At final clarifiers • Ahead of effluent filters • Considerations: • Effective mixing • Flexibility • Sludge production

14. Advanced Treatment Systems How is N removed or altered by conventional secondary (biological) treatment?

15. How is N removed or altered by secondary (biological) treatment? • Biological assimilation BUG = C60H86O23N12P • 0.13 lb N/lb of bug mass • Biological conversion by nitrification and denitrification

16. Nitrification • NH4+ Nitrosomonas  NO2- • NO2- Nitrobacter  NO3- • Notes: • Aerobic process • Control by SRT (4 + days) • Uses oxygen  1 mg of NH4+ uses 4.6 mg O2 • Depletes alkalinity  1 mg NH4+ consumes 7.14 mg alkalinity • Low oxygen and temperature = difficult to operate

17. Denitrification • NO3- denitrifiers (facultative bacteria)  N2 gas + CO2 gas • Notes: • Anoxic process • Control by volume and oxic MLSS recycle to anoxic zone • N used as O2 source = 1 mg NO3- yields 2.85 mg O2 equivalent • Adds alkalinity  1 mg NO3- restores 3.57 mg alkalinity • High BOD and NO3- load and low temperature = difficult to operate

18. Advanced Treatment Systems What are typical flow application rates in tertiary filters?

19. What are typical flow application rates in tertiary filters? • Automatic backwash filters (1-2 ft media depth) = 2 to 4 gpm/sf • Deep bed filters (4-6 ft media depth) = 4 to 8 gpm/sf

20. Advanced Treatment Systems What are typical backwash rates for a tertiary filter (in gpm/sf)?

21. What are typical backwash rates for a tertiary filter (in gpm/sf)? • Automatic backwash filters • 20 to 25 gpm/sf • 5 to 10% of throughput • Deep bed filters • 15 to 20 gpm/sf • 3 to 5% of throughput

22. Advanced Treatment Systems Define advanced treatment…

23. Define advanced treatment … • Treatment that improves or enhances secondary treatment processes • Further removal of organics, nutrients and dissolved solids

24. Advanced Treatment Systems Explain circumstances under which advanced treatment may be necessary…

25. Explain circumstances under which advanced treatment may be necessary… • Limited assimilative capacity of stream • Toxicity reduction / elimination • Nutrient control • Closed systems • Water reuse

26. Advanced Treatment Systems Identify and explain the objectives of the following advanced treatment systems: • Further removal of organics • Further removal of suspended solids • Nutrient removal (N and P) • Removal of dissolved solids

27. Identify and explain the objectives of the following advanced treatment systems: • Further removal of organics • Reduce effluent BOD to reduce receiving stream DO depletion • Improve disinfection • Reduce effluent N to improve water quality • Further removal of suspended solids • Removing TSS removes BOD • Removing TSS removes N and P (BUG = C60H86O23N12P) • Protects stream  sediment oxygen demand • Improves efficiency of disinfection

28. Identify and explain the objectives of the following advanced treatment systems: • Removal of nutrients (N and P) • Reduce oxygen demand of receiving stream • Control nutrients and algae • Control taste and odor in downstream drinking water • Suitability for reuse (examples: boiler water recycle, irrigation – N&P control of runoff, groundwater recharge)

29. Identify and explain the objectives of the following advanced treatment systems: • Removal of dissolved solids • Removal of specific pollutant – zinc, chromium, lead • Pretreatment of industrial waste • Control effluent toxicity • Make suitable for reuse

30. Activated carbon adsorption Chemical coagulation Flocculation Phosphorus removal Nitrogen removal Effluent Filtration Polishing lagoons Nitrification Denitrification Ammonia striping Alum or ion precipitation Lime precipitation Reverse osmosis (RO) Electrodialysis Advanced wastewater treatment…Describe the purpose or procedure and mechanism by which it is done for each of the following:

31. Activated Carbon Adsorption • Purpose • Tertiary treatment • Removal of low concentration organic compounds • Application: Influent Primary Trt Biological Trt  Filtration Carbon Disinfection • Many variations

32. Continued … Activated Carbon Adsorption • Carbon Regeneration • 5 to 10% loss • Less capacity than new carbon • Hot air @ 350oF • Chemicals (sodium hydroxide) • Fire / Explosion • Carbon usually replaced after 5 regenerations • Mechanism: • Active sites “Activated Carbon” • Molecular bonding • Particles adhere to surface

33. Chemical Coagulation • Purpose • Enhanced removal of organics and fine particles • Addition of lime, alum, iron, polymer to change ionic charge • Application • Chemical feed with rapid mix • Ahead of final clarifiers • Ahead of filtration

34. Continued … Chemical Coagulation Lime+ Heavy metalsAlum+ SS removal SS removalP removal P removal Polymer+ - SS control Iron+ SS removal P removal Mechanism: • Destabilization by ionic charge neutralization • Reduce charge that keeps small particles apart Aluminum sulfate Ferric chloride Ferric sulfate Ferrous sulfate _ _ _ _ + + _ + + _ _ _ + + _ + + + + _ _ + _ _ + + + _ + + _ + + + + + + _ _ + _ _ + _ _ + + + + _ _ + _ _ _ _ _ + _ + + + + + +

35. Flocculation • Purpose • Produce larger, more dense floc particles that will settle or filter easily • Application • Gentle mixing after rapid mix (coagulation) • Mixing – Mechanical or Aeration Q Infl Q Gentle Mix / Flocculation Rapid Mix / Coagulation Sludge

36. Continued … + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Flocculation • Mechanism • Coagulated particles strung together into larger floc particles (snow flake floc)

37. Phosphorus Removal • Purpose • Reduce effluent P • Biological or chemical method • Reduce nutrient load on stream • Reduce algae growth • Reduce oxygen depletion • Application / Mechanism • Biological • Chemical

38. Continued … Q Anaerobic Zone Aerobic Zone Final Clarifier Effl P Release P Luxury Uptake RAS WAS P Removal Phosphorus Removal • Biological

39. Continued … Phosphorus Removal • Chemical Primary Clarifier Aerobic Zone Effl Final Clarifier Q Chemical Coagulant Chemical Coagulant RAS WAS P Removal

40. Nitrogen Removal • Purpose • Reduce effluent N (ammonia and nitrates) • Biological or chemical • Reduce nutrient load on stream • Reduce algae growth • Reduce oxygen depletion • Application / Mechanism • Advanced Activated Sludge Processes • Nitrification (remove ammonia) NH4  NO2  NO3

41. Continued … Nitrogen Removal • Denitrification (remove nitrate) NO3 NO2  NO, N2O or N2 gas • Deep Bed Filtration • Anaerobic fixed film bacteria (denitrify) • Air Stripping • Removes ammonia • Elevated pH 10.8 to 11.5 NH4 as gas Q Media 6-8’ Methanol (carbon) Q

42. Purpose Remove SS (usually after FC) Reduce BOD and insoluble P Application Deep Bed 4-6’ sand and gravel Large cells 10’ x 30’ Similar to WTP (batch backwash) hL = 4 - 6 ft $$$ 2. Traveling Bridge 1-2’ sand and anthracite Small cells 1’ x 14’ Contiuous backwash hL = 2 - 3 ft Effluent Filtration

43. Continued … Effluent Filtration • Loading Rate • Backwash • 2 – 4 gpm/sf • Frequency depends on loading • 20 – 25 gpm/sf • 5 – 15% of throughput • Must clean beds • Air scour • Mechanism • Filtration by granular media

44. Polishing Lagoons • Purpose • To further treat or polish the effluent • After final clarifier • Facultative pond (aerobic and anaerobic) • Application • Typical volume = 1 day average flow i.e., 1 mgd plant = 1 mgd lagoon 24 hour detention time • Surface aerators

45. Continued … Polishing Lagoons Sunlight • Sunlight  Photosynthesis  Algae + Organics & Nutrients • Organic Matter  Anaerobic Decomposition • Mechanism Algae and bacteria grow in pond consuming organics and nutrients in FC effluent. Algae settles and degrades by anaerobic process. Surface Aerator Algae M Settling Aerobic Anaerobic methane gas

46. Nitrification • Purpose • Reduce ammonia on plant effluent • High ammonia concentrations are toxic to streams • Quickest impact on DO versus nitrates • Application • SRT > 3 days in activated sludge process • Grow Nitrosomonas and Nitrobacter • NH4  NO2 NO3 • Mechanism Biological conversion of ammonia to nitrate

47. Denitrification • Purpose • Reduce nitrate on plant effluent • Usually in combination with nitrification to reduce Total N to the stream • Application • Activated Sludge Process • Deep Bed Filters • Mechanism Biological conversion of nitrate to N2 gas Q Anx Oxic FC Oxic Recycle RAS WAS

48. Ammonia Stripping • Purpose • Reduce ammonia either before or after biological treatment • Not commonly used in the US • Application / Mechanism • Raise pH  10.8 to 11.5, usually by adding lime • Move equilibrium point to ammonia gas @ 250C and pH 11 • NH4 gas = 98%

49. Continued … Ammonia Stripping • Break wastewater into droplets and strip off ammonia gas with air • Freefall through tower that circulates a lot of air to remove ammonia to atmosphere NH4 Air Lime Q NH4 Stripper Floc Precip. Lime Sludge Air Q

50. Alum or Iron Precipitation • Purpose • To remove orthophosphate • Application • As a backup to Bio-P process • As chemical P removal • As chemical process • Mechanism • Al+ or Fe+ + PO4  Aluminum or Iron Phosphate Al+ or Fe+ Filtration Optional Q Q Precipitate Rapid Mix RAS WAS + Precipitate