Advanced nutrient removal in a continuous A2/O process based on partial nitrification-anammox and denitrifying phosphorus removal

Abstract

To resolve the issue of existing municipal wastewater treatment plants (WWTPs) in China having an insufficient influent carbon source, a continuous anaerobic-anoxic-aerobic (A2/O) process was established to treat low C (chemical oxygen demand; COD)/N (total nitrogen; TN) (C/N < 3) synthetic wastewater. The effects of the volume ratio of anaerobic, anoxic, and aerobic zones (Vana:Vano:Vaer) and the dissolved oxygen (DO) concentration in the aerobic zones on the performance and pathway of nutrient removal were investigated. During the 260 d experimental period, highly efficient nutrient removal was achieved based on partial nitrification-anammox (PNA) and denitrifying phosphorus removal (DPR) with COD, ammonia nitrogen (NH4+-N), TN, and total phosphorus (TP) removal rates of 81.55 %, 97.69 %, 87.82 %, and 93.60 %, respectively. The outcomes demonstrated that partial nitrification (NO2−-N accumulation rate of 61.38 %) can be achieved under the DO concentration of 0.3–0.7 mg/L and the ratio of Vana:Vano:Vaer = 1:4:3 (phase 6). PNA can be achieved by adding suspended carriers to the anoxic zones (phase 7) after NO2--N build-up. Moreover, the relative abundance of anammox bacterial at the genus level in the anoxic-carrier biofilm increased to 1.37 % in the end of phase 7. Meanwhile, the TP removal performance was improved significantly with the configuration of the pre-anoxic zone in phase 7; a DPR rate of 56.43 % (phosphate phosphorus uptake concentration of 4.41 mg/L) occurred in the anoxic zones and the following phosphate phosphorus uptakes in the aerobic zones was 5.18 mg/L. This study suggests that the continuous A2/O process can achieve advanced nutrient removal based on PNA and DPR without carbon addition by conventional process optimisation under insufficient carbon source conditions, which provides a reference for improving the nutrient removal performance in practical engineering applications.