Nutrient Removal and Power Savings in Wastewater Treatment Systems Todd L. Steinbach, PE

1. Aero-Mod® Wastewater Process Solutions Nutrient Removal and Power Savings in Wastewater Treatment Systems Todd L. Steinbach, PE

2. Energy Consumption What determines the amount of aeration required in an activated sludge plant? It can be the organic loading (Organic Requirement)… but it is often the amount of energy required to keep the basin(s) in suspension (Mixing Requirement). How does an under-loaded plant operate energy-efficiently? How does this relate to Nitrogen Removal?

3. Organic Requirement Oxygen required by the bacteria to break down BOD and ammonia. For Extended Aeration: 1 lb of BOD requires from 1.33 to 1.5 lbs of O2. 1 lb of ammonia requires 4.6 lbs of O2.

4. Organic Requirement 1.0 MGD Typical Example: BOD: 240 mg/l, NH3-N: 35 mg/l, 1.5 lbs O2/lb BOD, 24 hr HRT, 11’ water depth, fine bubble efficiency of 2.0%/ft of subm., 5.5 psi, 1,000 FASL, summer temp. O2 for BOD would be 325 lbs/hr, …or 1,409 scfm (1,656 icfm) of blower air. O2 for NH3-N would be 145 lbs/hr, …or 630 scfm (741 icfm) of blower air.

5. Organic Requirement 1.0 MGD Typical Example: Blower Power Required, assuming pd blower @ 70% efficiency BHP for BOD = (icfm) * (psi) / (229 * eff%) = (1,656 icfm) * (5.5 psi) / (229 * 70%) = 57 HP BHP for NH3-N = (icfm) * (psi) / (229 * eff%) = (741 icfm) * (5.5 psi) / (229 * 70%) = 25 HP 82 HP Total (sizing program gave me 79 HP)

6. Mixing Requirement 1.0 MGD Typical Example: Side-roll aeration, 20 cfm/1,000 cf, 24 hr HRT, 11’ water depth, 5.5 psi, 1,000 FASL, summer temp. Air required for mixing would be: cfm = (1 Mgal) / 7.48 cf/gal / 1,000 cf * 20 cfm = 2,674 cfm BHP = (2,674 cfm) * (5.5 psi) / (229 * 70%) = 92 HP (sizing program gave me 89 HP)

7. Energy Consumption What determines the amount of aeration required in an activated sludge plant? It can be the organic loading (Organic Requirement)… but it is often the amount of energy required to keep the basin(s) in suspension (Mixing Requirement). How does an under-loaded plant operate energy-efficiently? How does this relate to Nitrogen Removal?

8. Nutrient Discharge Limits • Ammonia toxicity to aquatic organisms • Nitrite toxicity to aquatic organisms • Nitrate toxicity to humans • Methemoglobinemia (blue baby syndrome) • Eutrophication • Fertilization

9. Aero-Mod® Wastewater Process Solutions Ammonia

10. Ammonia Reduction • Oxidation of Ammonia • Urea (CH4N2O) => NH3 => NO3- • Protein => Amino Acid => NH3 => NO3-

11. Nitrification • Nitrification is accomplished by two unrelated groups of autotrophic microorganisms • Ammonia-oxidizing bacteria such as Nitrosomonas • Nitrite-oxidizing bacteria such as Nitrobacter

12. Nitrification • Consumes 4.6 grams of O2 per gram of NH3-N oxidized • Consumes 7.1 grams of alkalinity per gram of NH3-N oxidized • Forms 0.15 grams of new cells per gram of NH3-N oxidized

13. Nitrifying Bacteria • Nitrite oxidizers cannot proliferate until the ammonia oxidizers have produced enough nitrite for the nitrite oxidizers • Different species nitrify at different D.O. levels • Clusters of ammonia oxidizers and nitrite oxidizers appear to grow close together within the floc • Nitrifiers need NH3-N, not NH4+-N

14. Wastewater Characteristics that Impact Nitrification • SRT • Temperature • pH • Alkalinity • D.O.

15. Wastewater Characteristics that Impact Nitrification • SRT • Typically, at least 5 days will be required for stable nitrification

16. Wastewater Characteristics that Impact Nitrification • Temperature • Colder temperatures require an older sludge age because reproduction slows down • Colder temperatures cause more of the ammonia to be ionized (NH4+)

17. Wastewater Characteristics that Impact Nitrification • pH • Nitrifiers are sensitive to changes in pH • As pH decreases, ionization increases and less NH3-N is available

18. Wastewater Characteristics that Impact Nitrification • pH vs. Alkalinity • pH is a measure of hydrogen ion concentration • Alkalinity is a measure of a water’s ability to neutralize acid • Water with high alkalinity will always have an elevated pH, but a water with elevated pH does not always have a high alkalinity • Both measurements are needed

19. Wastewater Characteristics that Impact Nitrification • Why Low Alkalinity Affects Nitrifiers • pH • Alkalinity neutralizes acid • Inadequate alkalinity results in low pH • Carbon Source • Nitrifiers cannot use organic compounds for synthesis and growth • Bicarbonate/carbonate alkalinity may satisfy their need for an inorganic carbon source

20. Wastewater Characteristics that Impact Nitrification • Chemical Sources of Alkalinity • For every mg of _______ added, _______ mg of alkalinity as CaCO3 is gained CaO Quick Lime 1.8 Ca(OH)2 Hydrated Lime 1.4 Mg(OH)2 Magnesium Hydroxide 1.4 NaOH Caustic 1.2 Na2CO3 Soda Ash 0.9

21. Wastewater Characteristics that Impact Nitrification • Dissolved Oxygen • Nitrification is an aerobic process and elemental oxygen (O2) is required • Nitrifiers may not compete as well for oxygen as heterotrophic bacteria • If not enough oxygen is present, the heterotrophs may get most of it first

22. Problems Caused by Nitrification • Large oxygen requirement • Potential low pH (if alkalinity is low) • If pH is low, fungi can develop • Discharge of nitrogen as Nitrate • Potential for clarifier denitrification • Sludge age range where filaments can develop

23. Aero-Mod® Wastewater Process Solutions Nitrogen Removal

24. Denitrification • The other half of biological nitrogen removal • Accomplished by many different kinds of facultative bacteria • Facultative bacteria can use oxygen or nitrate • Denitrifiers are facultative heterotrophs and must have an organic carbon food source • Bacteria forced to use the oxygen in Nitrate

25. Denitrification • Bacteria reuse about 60% of nitrification O2 • Produces 3.6 grams of alkalinity per gram of Nitrate reduced (about 50%) • Forms about 0.5 grams of new cells per gram of Nitrate reduced • Consumes about 2.9 grams of BOD per gram of Nitrate reduced

26. Denitrification Methods • Anoxic zone with nitrate recycle from aeration tank • High recycle rate of 2Q to 4Q • Sequenced aeration • Low D.O. operation • D.O. Probes & Controller • VFD Motor Drives • PLC Process Controller

27. Denitrification Designs • A2O and Bardenpho • SBR • Oxidation Ditch w/ Mixed Anoxic Zone • MBBR (Moving Bed BioReactor) • Step feed aeration • SEQUOX

28. Denitrification Designs

29. Denitrification Issues • D.O. level too high will prevent bacteria from using NO3- • Lack of carbon source available for bacteria • Recycle rate too low will not bring back enough Nitrate • Recycle rate too high will shorten detention time of aeration basin • High peak flows in an SBR reduces allowed time for aeration on and aeration off • High fluctuations of BOD/ammonia disrupt D.O. level

30. Aero-Mod SEQUOX Solution 2nd Stage Aeration (Air-off) Supernatant Effluent Aerobic Digestion Clarification 1st Stage Aeration (Air on) RAS WAS Influent Bio-Selector WAS RAS 1st Stage Aeration (Air off) Aerobic Digestion Clarification Effluent 2nd Stage Aeration (Air on) Supernatant

31. Aero-Mod SEQUOX Solution2 hours later 2nd Stage Aeration (Air on) Supernatant Effluent Aerobic Digestion Clarification 1st Stage Aeration (Air off) RAS WAS Influent Bio-Selector WAS RAS 1st Stage Aeration (Air on) Aerobic Digestion Clarification Effluent 2nd Stage Aeration (Air Off) Supernatant

32. SEQUOX Nitrogen Removal Process • Denitrification without mixers • Sequenced aeration with continuous clarification • Reclaim portion of oxygen & alkalinity consumed in nitrification • Concentrated settled biomass consumes D.O. quickly • Oxygen-starved biomass uses nitrates quickly when basin is re-aerated • Plug flow pattern ensures several cycles of sequenced aeration • Common-wall construction provides smallfootprint

33. SEQUOX Features SEQUOX controls: • Where we the air is placed (only 50% of basins aerated at a time) • When we aerate basins (simple timer control on typical 2-hour cycle) • How much air we provide via VFD control on the aeration blowers • How fast we allow the D.O. to rise in the Aeration Basins using a PLC-based D.O. control system to control each blower VFD

34. SEQUOX with DO2ptimizer Benefits Energy Savings a. When D.O. is below low set point, blower output increases. (Organic Requirement) b. When in-between low and high set points, blower output decreases to mixing requirement. (Mixing Requirement) c. When above high set point, blowers can be turned off. (Rest) 2. Flexibility when organic loading is high, plant can automatically switch to SEQUOX (both 1st Stage Aeration Basins aerating) and when the organic loading subsides – go back to SEQUOX-Plus. 3. Nitrogen Removal levels to Total N of 3 mg/l achieved.

38. NEYCSA - Mt. Wolf, PA 1.70 MGD

39. Neligh, NE • 210,000 gpd municipal facility • One 30 HP blower for process and aerobic digester • Blower operated with manual control of VFD for nine years • PLC-based D.O. control placed into operation in Fall of 2011 • Average of 5,000 kWh reduction per month ≈ $500 savings per month • Along with the power savings, plant is also achieving TN reduction

40. Holton, Kansas 0.528 MGD Bio-P

41. Ammonia Removal - Nitrification • Ammonia is oxidized by nitrifying bacteria • Bacteria use oxygen to strip carbon from alkalinity and hydrogen from ammonia • Bacteria use 7.1 mg alkalinity per mg ammonia reduced • Bacteria use 4.6 mg oxygen per mg ammonia reduced • Nitrate is reduced product – NO3-

42. Nitrogen Removal - Denitrification • Nitrate is reduced by heterotrophic bacteria • Bacteria use the oxygen from nitrate • DO must be controlled to force the bacteria to use the nitrate • Alkalinity is reclaimed – about 3.6 mg per mg of nitrate • A carbon source must be available for the bacteria to use

43. Energy Consumption What determines the amount of aeration required in an activated sludge plant? It can be the organic loading (Organic Requirement),… but it is often the amount of energy required to keep the basin(s) in suspension (Mixing Requirement) How does an under-loaded plant operate energy-efficiently? USING SEQUOX & AERO-MOD’S DO2PTIMIZER

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45. Custom Designed Wastewater Treatment Solutions www.aeromod.com