Biological Phosphorous Removal An Operator’s Guide

Glenn Burkhardt, PE

Engineered Logic LLC

What is Bio P Removal?

• It is NOT a mysterious brown box

Bio P Model

• Two Step Process (Anaerobic then Aerobic)

Acetate + Poly-P → PHA + ATP → H20 + CO2

← Anaerobic → ← Aerobic →

Bio P Process Discussion

• Anaerobic Step • Carbon Conversion to Volatile Fatty Acids

• Volatile Fatty Acid Conversion to Acetate

• Acetate & Poly-P Conversion to PHA & ATP

PHA Polyhydroxyalkanoic Acid

ATP Adenosine Triphosphate

• Aerobic Step • PHA & ATP Conversion to Glycogen, H2O & CO2

Phosphorous Uptake Diagram

Anaerobic→← Aerobic

0

10

20

30

40

50

60

0 25 50 75 100 150 200 300

Treatment Process Diagram

• A/O Process

Anoxic Zone

Aerobic Zone

Important Design Parameters

• BOD to P ratio > 20

• COD to P ratio > 45

• VFA to P ratio > 7

• Anaerobic HRT 1 to 2 hours

• Aerobic SRT 15 to 20 days

• Nitrate Loading < O2 Demand of Waste

Important Operating Parameters

• Anaerobic Zone pH 8.0 to 8.5

• Anaerobic Zone ORP -100 to -200 mV

• Aerobic Zone pH 7.0 to 7.5

• Aerobic Zone ORP +100 to +300 mV

• Return Sludge Rate Manage ML Conc.

Maintain ORP Limits

pH and ORP Monitoring

Bio P Troubleshooting

• Phosphorous Increasing (normal NH3 & SS) • P uptake could be due to low VFA production

• ATP production could be affected by anaerobic pH

• Nitrates could be affecting anaerobic conditions

• Parameters to Check • VFA to P ratio (greater than 7)

• Anaerobic reactor pH (8.0 to 8.5)

• Anaerobic reactor ORP (-100 to -200 mV)

Bio P Troubleshooting

• Rapid P Increase (normal NH3 & SS)

• Side Stream with High P Being Introduced

• P Release from Clarifier Sludge Blanket

• P Release from High Solids Retention time

• Parameters to Check

• P Concentration to Anaerobic Reactor

• ORP of Sludge Blanket ( 0 to 100 mV is the goal )

• Soluble P of Mixed Liquor ( < 0.5 mg/l is the goal )

Bio P Troubleshooting

• High Effluent P ( high effluent SS)

• Could be due to High Effluent Solids

• Could be due to P Release

• Could be due to Aerobic Reactor pH

• Parameters to Check

• Check P of Filtered Effluent Sample

• Check P Profile of Anaerobic and Aerobic Reactors

• Check pH of Anaerobic and Aerobic Reactors

Bio P Performance

• Improved Solids Settling Characteristics

• Less Risk of Aerobic Reactor Foaming

• More Stable Under Shock Loading Conditions

• No Chemicals Required

• Less Sludge Production

• Effluent P Typically 0.2 to 0.5 mg/l

• Effluent NH3 Typically < 0.5 mg/l

Questions?

Glenn Burkhardt, PE

Engineered Logic LLC