Functional guild dynamics in a single-sludge shortcut nitrogen and phosphorus removal reactor: a modeling study

Abstract

Mathematical modeling is a useful approach to study complex bioprocesses across a much broader range of scenarios then is feasible in experimental systems. A mathematical bioprocess model based on a novel integrated shortcut nitrogen and phosphorus removal reactor treating low strength municipal wastewater was set up and used to elucidate guild abundance and process performance under different operational conditions. Our specific objective was to identify operational factors, including intermittent aeration frequency, the ratio of anoxic and aerobic time, anaerobic duration, and the dissolved oxygen (DO) setpoint, to establish the boundaries for NOB out-selection, understand the main mechanisms for NOB activity suppression, and optimize operational conditions to enhance overall nutrient removal efficiency. Results showed that aerobic interval times shorter than 20 min effectively reduced NOB growth rate and suppressed NOB activity with minimal impact on ammonium oxidation bacteria (AOB) activity, resulting in a robust nitrite accumulation ratio (NAR) of over 85%. Longer anoxic time and lower DO levels had a more significant impact on NOB compared to AOB. The resulting NAR was higher than 93% with anoxic times longer than 5 min, while it was higher than 80% with DO levels lower than 0.8 mg L⁻¹. Intermittent aeration mode maintained a constant ratio of the specific growth rate of polyphosphate accumulating organisms (PAO) to denitrifying PAO (DPAO). Effective removal of total phosphorus (TP) was maintained when the anaerobic time allowed for sufficient carbon uptake. In conclusion, our findings suggest that a combination of high intermittent aeration frequency, an elevated ratio of anoxic to aerobic time, and a low DO setpoint can effectively reduce the specific growth rate of NOB and maintain robust NOB suppression. When combined with adequate anaerobic residence time, this approach allows for shortcut nitrogen and biological phosphorus removal in a single-sludge reactor.