Optimizing aeration rate in an external nitrification–denitrifying phosphorus removal (ENDPR) system for domestic wastewater treatment

• A prominent ENDPR system was developed and operated with low HRT and low COD/N.
• DPAOs could be temporarily inhibited under low aeration rate (DO = 0.2 mg L−1).
• Lower poly-P accumulated in the sludge was the direct cause of the deterioration of phosphorus removal.

A ENDPR system, combining anaerobic–anoxic–oxic reactor with an external nitrification biological aerated filter (AAO-BAF), was developed to treat real domestic wastewater. The effluent was discharged after full nitrification in BAF, while nitrogen and phosphorus removal by denitrifying phosphorus accumulating organisms (DPAOs) in the AAO reactor was achieved. To optimize aeration rate in the denitrifying phosphorus removal (DPR) reactor, oxidation–reduction potential (ORP) and DO was examined. When the aeration rate dropped to 20 L h−1, the phosphorus removal deteriorated greatly. During this phase, the polyphosphate (poly-P) amount in the sludge was reduced by 43% due to incomplete phosphorus uptake and the secondary phosphorus release. After increasing the aeration rate to 30 L h−1, the abilities of anaerobic phosphorus release and anoxic phosphorus uptake were both improved. Results demonstrated that AAO-BAF could be operated stably with high removal efficiencies of NH4+ (99%), TN (80%), and PO43- (94%) with low carbon requirement (COD/N ratio = 4.0) and low aeration rate (DO = 0.5 mg L−1, in AAO reactor).

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