1. Activated Sludge Aeration Control Systems Do 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 MLSS 14 Major Components
Soluble 8
Ordinary Heterotrophic Bacteria ra
COD N 9
Poly-P Heterotrophic Bacteria
Slowly- Biodegradable Colloidal
Slowly -Biodegradable Particulate N P
COD 2 3 4 P 10
Ammonia Oxidizing Bacteria rh rg 1 11 O2
Nitrite Oxidizing Bacteria
COD 12 rd
Methylotrophic
Bacteria
Particulate
Inert
Inert
Suspended
Solids 7 13
Endogenous
Products 5
Transformation Rates
a: adsorption g: growth
h: hydrolysis d death
COD N P 14
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
ANR
ANR: 1-3 hours
ANX: 1-2 hours
AER:4-12 hours
AER: 0.5 hours
ANR: 2–12 hours
Oxidation Ditch
SCL

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 setpoint typically 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 me.

25. Dave Kinnear