Study On Optimization And Control Of Six-tank Integrative Activated Sludge Denitrification And Dephosphorization Process

In view of the shortcomings of poor removal efficiency of nitrogen and phosphorus removal and high energy consumption of the existing secondary biochemical treatment in China's urban sewage treatment plants,Southeast University independently developed Six-Tank Integrative Activated Sludge Denitrification and Dephosphorization Process.Sludge and mixed liquid are recirculated automatically by location transition of inlet and outlet without additional sludge or mixed liquid recirculation.The alternation of anaerobic,anoxic,anaerobic,anoxic,aerobic required for denitrification and dephosphorization at the same time in time and space sequence is realized by controlling the changes in the state of each reaction tank.The operation parameters of the process were optimized by studying the effect of the process.The design function and process of denitrification and dephosphorization were analyzed by investigating the changes of water quality and state parameters in each reaction tank.And the feasibility to use ORP,DO and pH as control parameters for phase change was also discussed,the real-time control technology of phase change was established and confirmed on the basis of above study.The operation mode of the process was beneficial to the enrichment and cultivation of activated sludge.When the water temperature is 25-32?,sludge culture is completed in 23 days,and the process has achieved good nitrogen and phosphorus removal effectt,and the average removal efficiencies of CODcr,NH4+-N,TN,TP reached about 89%,94%,70%,87%respectively,the effluent of the system can stablely meet the first grade A standards of Urban Sewage Disposal Plant Integrated Discharge Standard.When the water temperature is 18?25?,the appropriate hydraulic retention time should be controlled at 13h or so,the DO concentration in the former aerobic tank should be controlled at 1.5-2.5mg/L or so.when the average concentrations of influent CODcr,NH4+-N,TN,TP were 191mg/L,29.1 mg/L,3.9mg/L respectively,the corresponding effluent concentrations reached 25.9mg/L,1.73 mg/L,7.99 mg/L and 0.45 mg/L,respectively.The water quality and state parameters of the reaction tanks in the upper half of the cycle were tracked and monitored,the results show that the variation of ORP,pH and DO of the state parameters has a good correspondence with the end of the reaction process.?At the end of denitrification,the ORP decreases rapidly,and an inflection point appears on the ORP curve.The pH changes from ascending to descending,and a turning point appears on the pH curve.?When it comes to the end of nitration,ORP and pH tends to be stable from falling,and the platform appeared on both ORP and pH curves.?During the process of aerobic nitrification and phosphorus uptake,DO slowly rises,and finally reaches 1.2?1.5mg/L.After nitrification and phosphorus absorption,DO jumps rapidly to 2.0mg/L,then it slowly increases.While the ORP roses to 70?80mV or so,then it rise slowly and tends to be stable,the pH rises from the drop.So ORP,pH,DO can be used as control parameters to establish the process phase conversion real-time control.The real-time control technology of phase change was established on the basis of above research.Using the established phase conversion real-time control technology for nitrogen and phosphorus removal research,the results show that the switching of the state can be realized in time and effectively,and the cycle running time can be shortened according to the set control rules.The comparison of the process performance between the real-time control technology of stage conversion and the operation performance of fixed-stage time control technology was carried out.The results show that the effluent quality can stablely meet the first grade A standards in real-time control technology,the removal rate of TN and TP under real-time control technology were 67.4%and 88.5%respectively,better than the removal rate under fixed time control technology(59.3%and 83.7%),and the operation of the process is more stable in real-time control technology.Therefore,the process has a highly efficient and stable nitrogen and phosphorus removal effect,the establishment of the stage conversion real-time control technology is basically feasible.