Research On Optimization Of A~2 / O Process For Biological Nitrogen And Phosphorus Removal

Tai Lake is one of the five largest freshwater lakes in China, is the most important water source of Shanghai, Suzhou, Wuxi, Changzhou and hangjiahu area. Tai Lake exist serious water pollution, 70% of water in Tai Lake has reached eutrophication. Recently cyanobacteria has outbreaked at times. Water supply failure has emerged in some cities around Tai Lake. Nitrogen and phosphorus are plant nutrition element that cause lake eutrophication. With economic development, increased urbanization and increased water consumption, wastewater treatment has lagged far behind. Sewage treatment plant run hard to meet the discharge standard. Therefore, whether the wastewater treatment plant could operate stable and meet the discharge standard would affect the safety of peoples daily life.LuCun sewage treatment plant in Tai Lake region is located in the southwest suburb of Wuxi, at the riverside of Beijing-Hangzhou Grand Canal. It is one of the largest sewage treatment plant in Wuxi City with a daily treatment capacity of 300,000 m3. It was constructed from four process. There are different problems in the operation and the processes need to be optimized in urgent. In this study, a lab scale model that simulated the operation condition of LuCun wastewater treatment plant was established and the operation parameters were optimized.The results indicated that the change of the sludge recycling ratio and the inner recycling ratio has little effect on COD removal. Under the same condition, when inner recycling ratio increased from 100% to 180%, the average removal rate of total nitrogen increased by 9%, the average removal rate of total phosphorus slightly declined. When sludge recycling ratio decreased from 100% to 60%, sludge concentration showed a mean decrease of 300mg/L, the average removal rate of total phosphorus increased by 5%, the average removal rate of total nitrogen slightly declined. Therefore, when inner recycling ratio was 180% and the sludge recycing ratio was 60%, the maximal nitrogen and phosphorus removal achieved. Under low temperature (8～12℃) condition, the average removal rate of ammonia nitrogen increased by 15% and the average removal rate of total nitrogen increased by 14% through adding medium in the second aerobic stage with adding volume ratio of 30%.Dissolved oxygen concentration is one of the most important operation parameters and the key of energy saving. The study was designed to control different dissolved oxygen concentration at different aerobic stage to optimize the performance of the process. The required DO concentration at first, second, third aerobic stage were recommended as 0 to 1 mg/L, 2 to 3mg/L and 2 to 3 mg/L, respectively.The field optimization was carried on in LuCun wastewater. A multi-parameter integrated control system combined biological phosphorus removal and chemical phosphorus removal was established on site..