Concentration of pollutants especially influent C/N in municipal wastewater is higher in the northern China than in the southern China. Therefore, it is difficult to keep efficient and stable removal of nitrogen and phosphorus by using conventional biological treatment processes because of the limitations and typical water quality in the southern China. In this study, a modified A/O step-feed process was operated at lab-scale to deal with the weak urban sewage and to remove simultaneously biological nitrogen (N) and phosphorus (P). Under the controlled conditions: influent COD/TN 5. 16, HRT 8. 7 h, SRT 15 d, MLSS 5. 66 g ? L"1 , sludge reflux ratio 75% , the volume ratio of anaerobic/anoxic/aerobic 4 : 8 : 10, DO 1. 0-1. 5 mg ? L"1 in three aerobic zones, continuous operation with six inflow distribution ratio 150 d, the optimal flow distribution ratio obtained was 20% : 35% : 35% ! 10% , and the values of COD, ammonia nitrogen, total nitrogen, total phosphorus in effluent were 33. 05 mg ? L"1 , 0. 58 mg ? L~l , 9. 26 mg ? L^1 and 0. 46 mg ? L"1 , respectively. These values were up to Grade A discharging standardof pollutants for municipal wastewater treatment plant (WWTP)(GB 18918-2002). The majority of COD in raw water was used as carbon source of anaerobic phosphorus release and denitrification processes, and more than 74% of carbon sources was utilized effectively. At the same time, the experiment also found that collaborative control of DO and ORP are not only useful for anaerobic phosphorus release but also for anoxic denitrification and aerobic nitrification.%采用改良A/O分段进水工艺处理我国南方低浓度、低碳氮比城市生活污水.在进水COD/TN为5.16,HRT为8.7h,SRT为15d,MLSS为5.66g·L-1,污泥回流比为75％,厌氧/缺氧/好氧体积比为4∶8∶10 条件下,通过设置6种不同进水流量分配比,控制各好氧段DO为1～1.5 mg·L-1,经过150 d的连续运行,得到系统最佳流量分配比为20％∶35％∶35％∶10％;在此工况下COD、氨氮、总氮、总磷出水水质分别为33.05 mg·L-1、0.58 mg·L-1、9.26 mg·L-1、0.46 mg·L-1,出水优于国家GB 18918-2002一级A排放标准.原水COD绝大部分作为厌氧释磷和反硝化脱氮所需碳源,系统对碳源有效利用率达74％; DO和ORP的协同控制可以作为系统厌氧放磷段的控制参数；同时亦可作为缺氧段反硝化完成和好氧段硝化完成的指示性参数.
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