Study On Optimization And Real-time Control Of Five-tank Integrative Activated Sludge Process

In view of the disadvantages that nitrogen and phosphorus removal efficiency can't meet the new requirements for drainage standards and high energy consumption in aeration area in China's urban sewage treatment plants,Southeast University,on the basis of UNITANK and A~2/O technologies,independently developed Five-Tank Integrative Activated Sludge Process which combined the characteristics of sequence batch process and continuous flow process.The process unit is highly integrated with five hydraulically connected rectangle tanks.By controlling the aerator and the position of the inlet and outlet,it can realize the alternation of overall influent flow and the switching of anaerobia,anoxia and aerobic state of each unit.Meanwhile,it can also realize the recirculation of sludge and mixed liquid automatically.The experimental results show that the process has higher nitrogen and phosphorus removal effect and low energy consumption.The hydraulic characteristics and operating parameters of the process were studied firstly.Secondly,under the optimum operating parameters,the changes of the concentration and state parameters(ORP,DO and pH)of the reaction tanks in the half cycle were investigated,which aimed at analyzing the mechanism of nitrogen and phosphorus removal in the process and the design function of each tank.Finally,real-time control of phase change technology strategy was established on the basis of above study.The main results are as follows:(1)Under clean water condition,the hydraulic characteristics of Five-Tank Integrative Activated Sludge Reactor under different HRT were studied and the experiments discovered that the retention rate of reactor was 12.42%which was the smallest when HRT=13 h.What's more,the reactor has stronger hydrodynamic mixing degree and lower dead-volume ratio than A~2/O in the same HRT.By the way,the mixing degree of the reactor D/UL increased from 0.173 at A~2/O to 0.223 in Five-Tank Integrative Activated Sludge Reactor,and the dead zone rate decreased from 17.4%to 14.4%.(2)The hydraulic retention time and the air/water ratio are the important parameters for the operation control of the process.When the water temperature is18~25?,the appropriate hydraulic retention time and air/water ratio should be controlled at 13 h and 30,respectively.Under this operating conditions,the removal rates of COD,,TN and TP were 82.4%,85.4%,70.3%and 85.4%and the effluent con centrations were 45.4 mg/L?4.0 mg/L?11.4 mg/L and 0.48 mg/L,all of which reached the first level A standard of pollutant discharge.(3)The concentration of the pollutants and state parameterswere tracked and monitored in the upper half cycle and the phenomenon of denitrifying phosphorus removal and Simultaneous Nitrification and Denitrification was found in the 2#pool and 4#pools.At the same time,the variation of ORP,DO and pH of the state parameters has a good correspondence with the changes of the concentration of pollutants:firstly,at the end of denitrification,an inflection point and a turning point appears on the ORP curve and the pH curve respectively;secondly,at the end of the release of phosphorus,the platform appeared on both ORP and pH curves;lastly,at the end of aerobic nitrification and phosphorus absorption,the DO curve suddenly rose and the platform and a break point appeared on the ORP curve and pH curve,respectively.Therefore,ORP,DO and pH can be used as control parameters to establish the process phase conversion real-time control.(4)The real-time control technology of phase conversion was established on the basis of process operation and data analysis.It was carried out and the results showed that the real-time control technology shortened 8.3%of the half cycle time and has a better effect of nitrogen and phosphorus removal than fixed time control technology.The removal rate of TN and TP rose from 67.9%and 82.7%under the fixed time control to 76.1%and 89.5%under the real-time control technology.Therefore,the optimized process has a efficient and stable nitrogen and phosphorus removal effect,which is suitable for the treatment of domestic sewage with low C/N in medium and small-sized towns,and the effluent could meet the first grade A standards of Urban Sewage Disposal Plant Integrated Discharge Standard.