activated sludge aeration control systems do we need 2.0 mg/l? dave kinnear hdr engineering...
TRANSCRIPT
Activated Sludge Aeration Control Systems
Do We Need 2.0 mg/L?
Dave KinnearHDR EngineeringCharlotte, 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 MLSS14 Major Components
Ordinary Heterotrophic Bacteria
Ammonia Oxidizing Bacteria
Nitrite Oxidizing Bacteria
EndogenousProducts
Slowly- Biodegradable
Colloidal
COD
Particulate Inert
N
P
COD
InertSuspended
Solids
ra
rh rg
Soluble
N
P
COD
rd
Chemicals/Precipitation
MethylotrophicBacteria
Transformation Ratesa: adsorption g: growthh: hydrolysis d death
Poly-P Heterotrophic Bacteria
Slowly -Biodegradable
Particulate
N
P
COD
2
3
4 5
6
7
8
10
9
12
11
14
13
1
Fed to reactorGrown in reactor
O2
Wastewater Treatment Energy Requirements
WERF: Energy Efficiency in Wastewater Treatment: North American OWSO4R07e
$2.8 B spent on WW Energy in 2009$1.51 B spent on WW Aeration2009 US GDP = $14 TAeration Energy = 0.01% of GPD
Wastewater Processes Cycle Metabolic Conditions
ANR
ANR: 1-3 hoursANX: 1-2 hoursAER:4-12 hoursANX: 1-2 hoursAER: 0.5 hoursANR: 2–12 hours
Oxidation DitchSCL
Autotrophic Oxygen Half-Saturation
- 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Dissolved Oxygen, mg/L
/m
mm
ax
m = mmax (DO/(Ks + DO))
Temperature and Other Affects
5 10 15 20 25 30 350%
50%
100%
150%
200%
250%
Temperature, C
/m
mm
ax
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.
