Comprehensive Analysis of Oxidation Ditch and High-Efficiency Multi-Cycle A²/O Processes Performance in Urban Wastewater Treatment

Oxidation ditch and Anaerobic–Anoxic–Oxic (A²/O) processes have been applied in urban wastewater treatment plants for decades, but the differences between two processes in engineering applications are less studied. Based on the continuous monitoring of Ningyang’s sewage treatment plant (Shandong, China) for one year, this study systematically analyzed the removal efficiencies of nutrients in the oxidation ditch and the modified high-efficiency multi-cycle A²/O processes. The results showed that chemical oxygen demand (COD) and total phosphorus (TP) removal in the modified high-efficiency multi-cycle A²/O process of the Phase II project was better than that in the oxidation ditch process of the Phase I project, and the average concentration of COD and TP in the effluent was 49.9% and 51.7% lower than that in the oxidation ditch process, respectively. The removal rate of ammonia nitrogen (NH₄⁺-N) by the two processes was basically the same, while the total nitrogen (TN) effluent concentration of the oxidation ditch process was 31.4% lower than that in the high-efficiency multi-cycle A²/O process. In summary, the high-efficiency multi-cycle A²/O process had a better treatment performance regarding nutrient removal than the oxidation ditch process under the same conditions. Furthermore, the engineering and operational costs of the high-efficiency multi-cycle A²/O process were lower.