Biological Phosphorus Removal Capability in SBR System Using External Recycle of Activated Sludge

It was found through test that there is limited capability for phosphorus removal by means of excess sludge wastage in biological system, and it is difficult for effluent to achieve TP ≤0.5 mg/L in the case of influent of TP ≥5 mg/L. A test was made in which the phosphorus-released sludge was returned by means of external recycle of activated sludge and phosphorus removal capability was improved by increasing sludge concentration in SBR system. The results show that when MLSS is 5 mg/L , and recycled sludge quantity is 1/8 of total sludge amount in the system with TP ≤11 mg/L and TN = 45 mg/L in influent, total phosphorus in effluent can certainly reach the grade 1 of integrated wastewater discharge standard with NH 3-N≤3.6 mg/L and TN removal rate ≥86% in effluent, and thus obtaining the optimal result in simultaneous removal of phosphorus and nitrogen.