Advanced nitrogen and phosphorus removal in the pre-denitrification anaerobic/anoxic/aerobic nitrification sequence batch reactor (pre-A2NSBR) treating low carbon/nitrogen (C/N) wastewater

• Solved the bottleneck of high ammonia residues in the conventional A2NSBR process.
• Achieved advanced nitrogen and phosphorus removal with low C/N domestic wastewater.
• ORP, pH and DO were demonstrated closely related with the nutrient removal.
• DPAOs was enriched with a high denitrifying phosphorus removal efficiency of 96.86%.

In order to treat domestic wastewater with high ammonia but low carbon source (low C/N ratio), a novel two sludge pre-A2NSBR system (anaerobic/anoxic/aerobic nitrification) was firstly developed by exchanging the sequence of aerobic nitrification and anoxic phase of the conventional A2NSBR process (anaerobic/aerobic nitrification/anoxic). The system was operated for 186 days to treat real domestic wastewater with low carbon/nitrogen (C/N = 4.03). Anoxic duration was adjusted and post-aeration phase was added to enhance nitrogen and phosphorus removal. Results indicate that adding post-aeration phase is indispensable to achieve enhanced phosphorus removal, the pre-A2NSBR system achieved a high denitrifying phosphorus removal efficiency of 96.86% with efficient utilization of limited carbon source. Specifically, the ammonia effluent was 0.46 mg/L, which solved the bottleneck problem of high ammonia residues in conventional A2NSBR process. The fluorescence in situ hybridization (FISH) results showed that PAOs was enriched and GAOs was inhibited in the A2SBR, nitrifiers also became dominant in the N-SBR. Moreover, the profiles variation of real-time online indicator such as pH, ORP and DO were demonstrated closely related with the nutrient removal performance, and based on this, it is possible or expected to establish the real time control strategy in the future.