BNR (Biological Nutrient Removal)
FLOW SCHEMES
Biological phosphorus and nitrogen removal can be achieved
with the SAF since the design incorporates sequential staged
operations as required for BNR flow schemes.
Phosphorus removal utilizes the anaerobic, balance tank (septic
tank) used prior to the SAF. Recycled sludge from the final clarifier
is mixed with the influent in this stage. Nitrogen removal is then
achieved via denitrification in the first cell of the SAF where, with
no air injected, and the introduction of recycled nitrified effluent
from the end of the process, the process becomes anoxic.
The latter SAF cells are fully aerated and BOD removal and
nitrification are achieved in these. Full BNR requires a fourcell
SAF, minimum.
Typically effluent from a full BNR scheme will be:
• BOD less than 10 mg/l
• Total nitrogen less than 5 mg/l
• Ammonia nitrogen less than 1 mg/l
• Total phosphorus less than 0.5 mg/l