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Activated Sludge Aeration Control Systems Do We Need 2.0 mg/L?

Activated Sludge Aeration Control Systems Do We Need 2.0 mg/L?. Dave Kinnear HDR Engineering Charlotte, NC. Outline. Wastewater Treatment Aeration Requirements The Activated Sludge Landscape Aeration Control System Evolution Ammonia-Based Aeration Control

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Activated Sludge Aeration Control Systems Do We Need 2.0 mg/L?

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  1. Activated Sludge Aeration Control SystemsDo We Need 2.0 mg/L? Dave Kinnear HDR Engineering Charlotte, NC

  2. Outline • Wastewater Treatment Aeration Requirements • The Activated Sludge Landscape • Aeration Control System Evolution • Ammonia-Based Aeration Control • Literature on DO effect on Performance • 2.0 mg/L: Requirement or Myth?

  3. Wastewater Aeration Requirements • Biochemical Oxygen Demand • 1.0 lb Oxygen/lb BOD • Ammonia Removal • 4.8 lb Oxygen/lb NH3 • Denitrification • COD utilized for denitrification does not require oxygen • 2.8 lb oxygen recovered/lb NO3 removed • Increased SRT increases transfer efficiency • Increased Tank Depth increases transfer efficiency • Decreased DO concentration increases transfer efficiency Energy Saving Benefits of Denitrification (Rosso and Stenstrom, 2007)

  4. ASM Model MLSS14 Major Components Soluble 8 Ordinary Heterotrophic Bacteria ra COD N 9 Poly-P Heterotrophic Bacteria Slowly -Biodegradable Particulate P Slowly- Biodegradable Colloidal 10 Ammonia Oxidizing Bacteria rh rg 2 1 COD N 11 O2 Nitrite Oxidizing Bacteria COD P 3 12 rd Methylotrophic Bacteria Inert Suspended Solids 7 Particulate Inert 13 Endogenous Products 5 4 Transformation Rates a: adsorption g: growth h: hydrolysis d death COD N 14 P Chemicals/ Precipitation 6 Fed to reactor Grown in reactor

  5. Wastewater Treatment Energy Requirements $2.8 B spent on WW Energy in 2009 $1.51 B spent on WW Aeration 2009 US GDP = $14 T Aeration Energy = 0.01% of GPD WERF: Energy Efficiency in Wastewater Treatment: North American OWSO4R07e

  6. Wastewater Processes Cycle Metabolic Conditions SCL ANR ANR: 1-3 hours ANX: 1-2 hours AER:4-12 hours ANX: 1-2 hours AER: 0.5 hours ANR: 2–12 hours Oxidation Ditch

  7. Autotrophic Oxygen Half-Saturation m = mmax (DO/(Ks + DO))

  8. Temperature and Other Affects

  9. Aerobic SRT Requirement for Autotrophs • Don’t really care about m, you care that system SRT w/ safety factor (aerobic SRT) > washout SRT. • Nitrification capacity can be adjusted by: • Increasing DO • Changing aerobic SRT • Adjusting aerobic volume • SRT = 1/m Grady, Daiger and Lim. Biological Wastewater Treatment

  10. Outline • Wastewater Treatment Aeration Requirements • The Activated Sludge Landscape • Aeration Control System Evolution • Ammonia-Based Aeration Control • Literature on DO effect on Performance • 2.0 mg/L: Requirement or Myth?

  11. The Activated Sludge Landscape • DO (and other substrates) and MLSS component concentration not constant throughout reactor. • Allows “Simultaneous Nitrification/Denitrification” (SND) to occur. Steve Liss

  12. Outline • Wastewater Treatment Aeration Requirements • The Activated Sludge Landscape • Aeration Control System Evolution • Ammonia-Based Aeration Control • Literature on DO effect on Performance • 2.0 mg/L: Requirement or Myth?

  13. Aeration Control System Evolution • Pre 1970: limited DO control due to lack of accurate, maintainable DO sensors • 1990s?: Accurate, maintainable DO sensors allow feedback control to maintain a DO set point, saving energy. • DO setpointtypically 2.0 mg/L Aeration Control – A Review (Amand, Olsson, Carlsson) WS&T Improving Nutrient Removal While Reducing Energy at Three Swiss WWTPs (Reiger, Takacs, Siegrist) WER

  14. Aeration Control System Evolution • Current Trend: Ammonia-Based Aeration Control • DO setpoint changes based on effluent ammonia • More SND Volume • DO drops less than 0.5 mg/L • Saves Energy • Saves Carbon Improving Nutrient Removal While Reducing Energy at Three Swiss WWTPs (Reiger, Takacs, Siegrist) WER

  15. Outline • Wastewater Treatment Aeration Requirements • The Activated Sludge Landscape • Aeration Control System Evolution • Ammonia-Based Aeration Control • Literature on DO effect on Performance • 2.0 mg/L: Requirement or Myth?

  16. Ammonia-Based Aeration Control • Provides benefits and Reiger reports no: • Deterioration of settling properties (increased SVI) • Increased nitrite in effluent • Deterioration of effluent quality (increase effluent particulate phase, effluent TSS) [PC] • Previous authors report these problems with low DO in aerobic bioreactor

  17. Outline • Wastewater Treatment Aeration Requirements • The Activated Sludge Landscape • Aeration Control System Evolution • Ammonia-Based Aeration Control • Literature on DO effect on Performance • 2.0 mg/L: Requirement or Myth?

  18. Palm, Jenkins and Parker (1980)

  19. HRSD CE Pilot A-Stage Data Mark Miller, HRSD/Virginia Tech PhD Candidate

  20. HRSD CE Pilot Data

  21. Echeverria, Seco, Ferrer (1992) WS&T

  22. Starkey and Karr (1984, JWPCF) • DO reduced from 5.0 mg/L to 0.4 mg/L. • At low dissolved oxygen concentrations, changes in suspended solids and BOD could be large enough to violate discharge permits

  23. Outline • Wastewater Treatment Aeration Requirements • The Activated Sludge Landscape • Aeration Control System Evolution • Ammonia-Based Aeration Control • Literature on DO effect on Performance • 2.0 mg/L: Requirement or Myth?

  24. 2.0 mg/L: Requirement or Myth? • Thorough literature review would be useful • Student • Professor with a student looking for a topic • WERF or other research effort – reproduce previous efforts and apply literature review to laboratory • References in papers cited here were not checked. • When do we need 2.0 mg/L DO in bioreactor and when do we not? • References in paper or email me.

  25. Dave Kinnear dkinnear@hdrinc.com 704 516-9167

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