Enhanced biological phosphorus removal (EBPR) is a wastewater treatment process that uses polyphosphate accumulating organisms (PAOs) to remove phosphorus. In the anaerobic zone, PAOs uptake volatile fatty acids produced by fermentation, which provides energy to break down polyphosphate and release phosphate. In the aerobic zone, PAOs consume the released phosphate to produce new polyphosphate, removing phosphorus from the mixed liquor. The process alternates between anaerobic and aerobic zones to maximize phosphorus removal through the metabolic activities of PAOs.

1. Nutrient Removal
Enhanced Biological
Phosphorous Removal
WATR-082: ADVANCED WASTEWAATER TREATMENT
SPRING 2019

2. Enhanced Biological Phosphorous
Removal
PAO – Polyphosphate accumulating organisms
Anaerobic zone of aeration basin
Aerobic zone of aeration basin
Aeration Basin
WAS
Clarifier
RAS
Primary
Effluent
1. Organics are fermented to VFAs
1. The VFAs are consumed
2. The VFAs are converted into
energy rich products
3. The energy for the conversion is
obtained from the breakdown of
polyphosphates in the PAO
5. With the depletion of
polyphosphate the organism is
now stressed
4. Polyphosphate breakdown
results in phosphate release
1. The energy rich products
provide energy for the
consumption of phosphate
producing polyphosphates
Phosphate
released
into mixed
liquor
Phosphate
removed
from mixed
liquor
What is happening in the anaerobic part of the basin What is happening in the aerobic part of the basin
Volatile
Fatty Acids
(VFAs)
Removal of PAOs
containing
phosphorous
The PAOs in the
anaerobic zone
The PAOs in the
aerobic zone