Improving nutrient removal of the AAO process by an influent bypass flow by denitrifying phosphorus removal

The possibility of influent carbon source usage by influent bypass flow strategy in the anaerobic–anoxic–oxic (AAO) process was investigated, aiming at enhancing biological nitrogen removal based on enriched denitrifying phosphate accumulating organisms (DNPAOs). Tests were made to verify whether nitrogen removal from brewage wastewater was improved effectively by increasing λ (denoted as the ratio of influent bypass flow rate to influent flow rate). λ applied in the study was 0, 0.1, 0.15 and 0.25. Results showed that the optimal λ was 0.15; the corresponding NH4+-N, PO43−-P and TN removal efficiency reached 90%, 95% and 85%, respectively; and the ratio of anoxic P uptake to aerobic P uptake was increased by 56.2%. Furthermore, the results also demonstrated that when the optimal λ was adapted to treat the low influent C/N ratio wastewater, TN removal efficiency was increased by 13.2%. Therefore, it was possible to optimize the operation of the AAO process by influent bypass flow under good denitrifying phosphorus removal performance.