The experimental parameters of phases I and II.

The effective elimination of nitrogen and phosphorus in urban sewage treatment was always hindered by the deficiency of organic carbon in the low C/N ratio wastewater. To overcome this organic-dependent barrier and investigate community changes after sulfur electron addition. In this study, we conducted a simulated urban wastewater treatment plant (WWTP) bioreactor by using sodium sulfate as an electron acceptor to explore the removal efficiency of characteristic pollutants before and after the addition of sulfur electron acceptor. In the actual operation of 90 days, the removal rate of sulfur electrons’ chemical oxygen demand (COD), ammonia nitrogen, and total phosphorus (TP) with sulfur electrons increased to 94.0%, 92.1% and 74%, respectively, compared with before the addition of sulfur electron acceptor. Compared with no added sulfur(phase I), the reactor after adding sulfur electron acceptor(phase II) was demonstrated more robust in nitrogen removal in the case of low C/N influent. the effluent ammonia nitrogen concentration of the aerobic reactor in Pahse II was kept lower than 1.844 mg N / L after day 40 and the overall concentration of total phosphorus in phase II (0.35 mg P/L) was lower than that of phase I(0.76 mg P/L). The microbial community analysis indicates that Rhodanobacter, Bacteroidetes, and Thiobacillus, which were the predominant bacteria in the reactor, may play a crucial role in inorganic nitrogen removal, complex organic degradation, and autotrophic denitrification under the stress of low carbon and nitrogen ratios. This leads to the formation of a distinctive microbial community structure influenced by the sulfur electron receptor and its composition. This study contributes to further development of urban low-carbon-nitrogen ratio wastewater efficient and low-cost wastewater treatment technology.城市污水处理中氮磷的高效去除始终受低碳氮比（Carbon/Nitrogen ratio, C/N）废水中有机碳匮乏的制约。为破解这一依赖有机碳的技术瓶颈，并探究投加硫基电子受体（sulfur electron acceptor）后微生物群落的变化规律，本研究构建了模拟城市污水处理厂（Wastewater Treatment Plant, WWTP）生物反应器，以硫酸钠作为电子受体，探究投加硫基电子受体前后特征污染物的去除效能。在为期90天的实际运行中，相较于投加硫基电子受体前，投加后化学需氧量（Chemical Oxygen Demand, COD）、氨氮与总磷（Total Phosphorus, TP）的去除率分别提升至94.0%、92.1%与74%。与未投加硫基电子受体的阶段I相比，投加硫基电子受体后的阶段II反应器在低C/N进水条件下的脱氮性能更为稳定高效；阶段II好氧反应器的出水氨氮浓度在第40天后始终低于1.844 mg N/L，且阶段II的总磷平均浓度（0.35 mg P/L）亦低于阶段I（0.76 mg P/L）。微生物群落分析结果显示，反应器内的优势菌属红杆菌属（Rhodanobacter）、拟杆菌门（Bacteroidetes）与硫杆菌属（Thiobacillus）在低C/N胁迫条件下，可能分别在无机氮去除、复杂有机物降解与自养反硝化（autotrophic denitrification）过程中发挥关键作用，进而形成受硫基电子受体及其组成调控的独特微生物群落结构。本研究可为城市低C/N比废水高效低成本污水处理技术的进一步发展提供支撑。