Enhancing bio-P removal by phosphate recovery from anaerobic supernatant

A previous modeling study predicted that phosphate removal and recovery could be combined in biological nutrient removal (BNR) processes, which would be beneficial for either improving bio-P removal effluent quality or lowering the influent COD/P ratio required for bio-P removal. To confirm the modeling prediction, an experiment with a traditional A²/O process was initiated. The experimental results were qualitatively in agreement with the modeling prediction. The minimal COD/P ratio required for the effluent standard (1 mg P/L) could be lowered from 35 to 25 with a stripping ratio of 20% at a phosphate recovery efficiency of 34%, which means a COD saving of 25–30% in bio-P removal. A practical experiment for phosphate recovery in a WWTP identified that HAP was a major form of precipitated compounds and that MAP was a minor form. Due to the higher contents of Ca^2 + and Mg^2 + in the influent to the WWTP (with groundwater mainly used for portable water), it was unnecessary to dose any extra chemicals for phosphate precipitation, and a pH value increased to ≥9 in the supernatant was all to be done.