Simultaneous Nitrification and Denitrification Associated Phosphorus Uptake Properties of Sludge Subjected to EBPR with Efficient Micro Aeration

Simultaneous nitrification and denitrification (SND) under low dissolved oxygen (DO) and anaerobic/aerobic(anoxic) enhanced phosphorus removal (EBPR) are two processes that can significantly reduce the energy and carbon required for nutrient removal. The combination of the two processes is expected to achieve biological nutrient removal with minimal requirement of oxygen and carbon. In this study, a lab-scale sequencing batch reactor (SBR) was operated to perform simultaneous nitrification and denitrification as well as phosphorus removal (SNDPR) with micro aeration. Polyphosphate-accumulating organisms (PAOs) dominated by Candidatus Accumulibacter phosphatis communities were gradually enriched in the reactor by adjusting the time of nitrite addition. The EBPR system showed a high phosphorus removal efficiency (phosphate in effluent <0.5 mg/L) and complete ammonia oxidation without accumulation of nitrite and nitrate under low dissolved oxygen (DO) concentration (controlled at 0.2 mg/L). Regular operation and batch test demonstrated that the sludge was capable of using nitrite as electron acceptor to take up phosphate, the maximum specific denitrifying phosphorus uptake rates of adding 10 mg/L and 50 mg/L NO2 -N to maximum specific aerobic phosphorus uptake rate were 44.9% and 87.2%, respectively. Moreover, phosphorus uptake was not observed after nitrite depletion unless air was supplied even with a minimum amount. Batch tests suggested that ammonia nitrogen was removed through simultaneous nitrification and denitrification rather than anaerobic ammonium oxidation, whereas ammonia oxidized bacteria (AOB) and nitrite oxidized bacteria (NOB) were found to be less active than PAOs under low DO environment.