Comparison of Nitrogen and Phosphorus Removal between Two Typical Processes under Low Temperature in a Full-Scale Municipal Wastewater Treatment Plant

Given its strict discharge standards for wastewater treatment plants (WWTPs), China focuses on improving the removal effect of nitrogen and phosphorus in biological treatment processes under low temperatures. The variations in nitrogen and phosphorus during the anaerobic-anoxic-oxic (AAO) and AAO-sequencing batch reactor (SBR) processes in a full-scale WWTP were compared by sampling. Results showed that the removal efficiencies of total nitrogen (TN) and total phosphorus (TP) in both processes exceeded 85% and 91%, respectively, when the water temperature was lower than 15 degrees C. The wastewater treatment potential capacity of the AAO process was larger than that of AAO-SBR, indicating that the AAO process could realize the subjective demand of nitrogen or phosphorus removal by adjusting its operation mode. The anaerobic phosphorus release of the AAO process was affected when part of the internal reflux entered the anaerobic tank. Thus, the biological phosphorus removal of the AAO process was worse than that of the AAO-SBR process. Since the nitrification and denitrification rates of the AAO process were all higher than that of the AAO-SBR process, the TN removal efficiency of AAO was higher than that of AAO-SBR. These results could provide some advice for the upgrade, operation optimization, and process selection of both processes in the future.