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 Literature on DO effect on Performance 2.0 mg/L: Requirement or Myth?

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)

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

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

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

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

Temperature and Other Affects

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

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?

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

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?

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

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

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?

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

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?

Palm, Jenkins and Parker (1980)

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

HRSD CE Pilot Data

Echeverria, Seco, Ferrer (1992) WS&T

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

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?

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.

Dave Kinnear dkinnear@hdrinc.com 704 516-9167