Research On Process Optimization And Real-time Control Technology Of Improved A~2/O Process

Aiming at the problems like lack of carbon source and high aeration energy consumption in the progress of sewage water biological denitrification and phosphorus removal,our research group, proposed the " Pre-anoxic/Anaerobic/Low Oxic/Anoxic/Oxic" improved A2/O process system,it is based on the cascade A2/O2 process. The improvement of process can be reflected in:add a pre-anoxic tank between the hydrolysis tank and the anoxic tank, it can remove the nitrate nitrogen in the return sludge, then it can reduce nitrate nitrogen effect on anaerobic phosphorus release; low oxygen pool is divided into three parts, and different part have different dissolved oxygen concentration.Then on one hand it can achieve part of simultaneous nitrification and denitrification and on the other hand anoxic tank can have enough nitrate nitrogen to make the denitrifying phosphorus removal happen. Through experimental research, this paper explores the denitrification and phosphorus removal effect of the improved A2/O process, optimizes the process parameters, builds the mathematical model of the process so as to research the real-time control strategy and develop the improved A2/O process control and simulation software.The sewage of this study come from Wuxi campus of Southeast University, experimental results show that the optimal distribution ratio of the pre-anoxic tank and the Anaerobic tank is 1:4; The best DO concentration of the Low Oxic tank is 1 mg/L,1 mg/L,2.2 mg/L respectively, the suitable DO concentration for Oxic tank is 4 mg/L; The best hydraulic retention time of each tank is: Pre-anoxic tank 0.5h,Anaerobic tank 2h,Low Oxic tank3h,Anoxic tank 2 h,Oxic tank 1.5h, the total hydraulic retention time is 9h.When the influent concentrations of COD, TN, NH4+-N and TP are 140.55±0.85mg/L,25.77±0.59mg/L,20.11±0.36mg/Land3.89±0.25mg/L,The effluent concentrations of COD, TN, NH4+-N and TP are 17.26±2.25mg/L,8.98±0.71 mg/L,0.46±0.06 mg/L,0.32±0.04 mg/L,respectively.The removal rates of COD,TN,NH4+-NandTP are 87.72%,65.15%,97.71%,91.77%, respectively. The effluent water quality was lower than the first class Grade A of National Discharge Standard GB18918-2002 for Pollutants of Municipal Wastewater Treatment Plant.Choose ASM2D to simulate this process and build the improved A2/O process mathematical model. Research on the contaminant removal rate in different conditions when water temperature, flow rate and water quality changes, then we get the control strategy of the model. When temperature changes, the control parameters are DO, HRT and SRT. When the temperature falls, we can increase the DO value, the HRT and the sludge age; When the temperature rises, we can adjust nothing. When water flow changes, the control parameters are HRT and SRT. We Can increase or decrease each pool’s volume to make HRT remains the same, at the same time, we increase or decrease the excess sludge to make SRT maintain at about 15 days. When TN concentration change, the control parameters are DO, HRT, SRT and external carbon source. When TN concentration increases, we can reduce the DO value of the low oxygen tank, at the same time,we increase each pool’s volume. If it still not work, external carbon source can be used; When TN concentration decreases, we can adjust nothing. When TP concentration change, the control parameters are DO, HRT and SRT. When TP concentration decreases, we can increase DO value of the low oxygen tank and reduce the excess sludge to make SRT maintain at about 18.5 days; When TP concentration increases, we can increase DO value of the low oxygen tank and increase the anaerobic tank’s volume, we also need to increase the excess sludge to make SRT maintain at about 13 days. When the value of C/N changes, the control parameters are DO, HRT, SRT, water flow and external carbon source. When the value of C/N decreases, we can reduce the DO value of the low oxygen 3 tank and the oxic tank.If the value of C/N decreases largely,we can dose external carbon source; when the value of C/N increases, we can increase each pool’s volume and increase the DO value of the low oxygen 3 tank and the oxic tank. If the value of C/N increases largely,we can backflow the effluent water.Adjust various process parameters of the actual experiment based on the simulation results and adjustment strategies of the model, then the system can work stably and the effluent water quality is lower than the first class Grade A of National Discharge Standard GB18918-2002 for Pollutants of Municipal Wastewater Treatment Plant. Our group develop the improved A2/O process control and simulation software on the basis of the development, when When the water temperature, flow or water quality changes, the software can automatically get a parameter adjustment scheme.The SND and denitrifying phosphorus removal technology are applied to the improved A2/O process, which is a appropriate technology of sewage treatment with advantages of a good effect of nitrogen and phosphorus removal, energy conservation and adaptability to low ratio of C to N sewage.