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OXYGEN ACTIVATED SLUDGE –FROM BIO-PRECIPITATION TO HPOAS
Chi-Chung TangSanitation Districts of Los Angeles County
David JenkinsProfessor Emeritus
University of California at Berkeley
HPOAS process is a widely used biological wastewater treatment process
Philadelphia
Denver
Boston
LouisvilleNorfolk
HoustonNew Orleans
BaltimoreIndianapolis
Atlanta
Fort Lauderdale
Los Angeles County
SanFrancisco
Oakland
Los Angeles
Orange County
HendersonMorganton Rocky Mount
ConcordClinton
Fayetteville
Detroit
Jacksonville
El Paso
Tucson
Cincinnati
Miami
Tampa
Tacoma
Knoxville
Kansas City
Sacramento
The HPOAS process evolved from the “oxygen bio-precipitation” process
Oxygen bio-precipitation process has many desirable features
• High concentration of biological floc could be maintained
• Smaller reactor volume than air activated sludge process to achieve the same treatment level
• Could handle high organic loading; suitable for high strength wastewater
High PurityOxygen
Surface Aerator
Vent Gas
Primary Effluent
Return Activated
Sludge
ToClarifiers
: Gas Flow
: Water Flow
Union Carbide developed the UNOX®
process in 1966
The UNOX® process was successfully tested at pilot and plant scale at Batavia, NY
The UNOX® process is different from the air activated sludge process
0.2 – 0.60.4 – 1.0lb BOD5/lb MLVSS/d
F:M ratio
0.50 – 0.750.40 – 0.55lb VSS/lb BOD5
Sludge production
100 – 15030 - 70mL/gSVI
6 – 81 - 3HoursHRT
900 – 3,0003,500 – 8,000mg/LMLSS
1 – 24 – 8mg/LDissolved oxygen
Activated SludgeUNOX®UnitParameters
Detroit built the first UNOX® system in 1975
SDLAC provides wastewater treatment services to 5.3 millions residents
JWPCP is one of the largest HPOAS plants in the world
NN
JWPCP HPOAS process was constructed in two stages; operations began in 1983 & 2002
The JWPCP cryogenic plant can produce up to 625 TPD of high purity oxygen
Key design criteria of the JWPCP HPOAS process:
30%RAS Recycle Ratio12,000mg/LRAS TSS
mg/LDaysHoursmg/Lmg/LMGDUnit
3,000Mixed Liquor SS2.8Mean Cell Residence Time2.5Hydraulic Retention Time200Primary Effluent BOD5
150Primary Effluent TSS400Average Flow
Design
The standard four-stage UNOX® process was designed and first operated in 1983
High-Purity (98%) Oxygen
Primary Effluent and RAS
Oxygen Vent(~30% O2)
Mixed Liquor To Clarifiers
: Surface Turbine Aerator
Occasional sludge bulking and foaming problems were experienced
Filamentous bacteria were causing foaming and bulking sludge
“Anaerobic selector” selects floc formers and discourages nocardioform growth
WAS
EffluentClarifier
RAS
Anaerobic Selector Aerobic Reactor
Influent
Stored Carbonaceous Material
Stored Polyphosphate
Sol P
Energy
Soluble BOD
Sol P
Energy
O2
CO2 + H2O
Anaerobic selectors were created by changing surface aerators to mixers
High-Purity (98%) Oxygen
Oxygen Vent
Primary Effluent and RAS
Mixed Liquor To Clarifiers
Air Air Vent
: Surface Aerator
: Mechanical Mixer
Concrete corrosion was another problem of the UNOX® process
Good Concrete
Corroded Concrete
Carbon dioxide lowers water pH resulting in concrete corrosion
0.00
0.05
0.10
0.15
0.20
0.25
0.30
6.2 6.3 6.4 6.5 6.6 6.7 6.8pH
Corrosion1983 - 1996
(inches) Stage 1
Stage 4
Process configuration was modified to strip CO2 and raise pH
High-Purity (98%) Oxygen
Oxygen Vent
Primary Effluent and RAS
Mixed Liquor To Clarifiers
Air Air Vent
This picture shows the oxygen vent stack and the air vent stack
JWPCP HPOAS process is very stable and produces excellent effluent water quality
• Effluent water quality -
• Solids production –0.8 lb VSS/lb BOD5 removed
615JWPCP effluent
3030Discharge limit
Total BOD5(mg/L)
TSS(mg/L)
Summary• Pioneering research by Dr. Okun on the oxygen
bio-precipitation process has had a profound impact on the wastewater treatment industry
• The HPOAS process has been modified and improved and has demonstrated its robustness and reliability
• HPOAS process will likely be more popular in the future due to its ability to control odors, air toxics, and greenhouse gases
Questions?
