Study On Denitrification Of Modified A2/O Process Through The Small Pilot Plant And STOAT Simulation Software During The Rainy Season

Water resources plays an important role in the economic development andresidents’ life. Today, water pollution seriously impact on the ecological environmentand residents’ life. We should take active measures to solve the problem of waterpollution while maintaining economic development. There are differences between theinfluent of rainy season and dry season of the sewage treatment plant in Kunming City.The water quality of influent is good during the late rainy season, but high inflow andlow of C/N will have impact on the normal and stable operation of the sewage treatmentplant. In modified A2/O process, pre anoxic zone is set in front of the anaerobic zoneand plays the role of biological selector and can improve the anaerobic environment anddenitrification. The characteristics of the modified A2/O process as follows: resistanceto impact load, the water quality of effluent is stable, flexibility to adjust parameters,good nitrogen and phosphorus removal effect, biochemical system for mixed sewagewith high treatment efficiency, requires for automatic control system is general, highsystem reliability, less maintenance. At present, most of large and medium-sized sewagetreatment plant using this process at domestic and abroad. This subject comes from thenational "the water body of Pollution Control and the governance Science andTechnology major special" in of the Dianchi Lake project topics first "combine the keytechnologies of the sewage interception with control pollution to use and demonstrationof Dianchi Lake project"(task numbered:2012ZX07102-001) sub-topics three"combine the key technologies of the urban initial rainwater high collection efficiencywith treatment facilities to use and demonstration" topic four "combine the sewagetreatment plants with regulation and storage facilities to use and operation moderesearch and demonstration"(task numbered:2012ZX07102-001-003).This study would explored the impact of low concentration influent ondenitrification of the A2/O process. In order to find out the influent characteristics ofLuo Longhe sewage treatment plant during rainy season, analyzed the water quality ofinfluent and effluent of a similar sewage treatment plant in Kunming during2012, anddetermined the influent quality during rainy season as follow: the concentration of COD,NH3-N, TN were150mg/L,25~30mg/L,30~35mg/L, respectively. The value of theinfluent flow is twice of the design value. Changing mixed liquor reflux ratio, sludgereflux ratio, DO and other parameters, conducted single factor experiment and the orthogonal experiment through the small pilot plant and STOAT simulation software.Obtained the optimal operating parameters of denitrification under the condition of lowconcentration influent during rainy season.The measured and simulated results show that the rainwater shock loads have anadverse effects on denitrification of the A2/O process. However, the value of theeffluent TN can be achieved the basic discharge standards in rainwater shock loadsperiod while excess emissions after shock loads. Through comparative analysis ofsteady-state analog values with measured values shows that the mathematical model andmodel parameters is reasonable. The results of single factor experiment and theorthogonal experiment simulation are similar to the measured results. Single factorexperiment analysis shows increased mixed liquor reflux ratio and sludge recycle ratio,reduced the concentration of dissolved oxygen can improve the total nitrogen removalrate, but too high of mixed liquor reflux ratio and sludge recycle ratio is not conduciveto TN removal. Therefore, mixed liquor reflux ratio, sludge recycle ratio, dissolvedoxygen concentration were200%,200%,1~2mg/L and2~3mg/L, respectively, thevalue of the effluent TN can be achieved the basic discharge standards. Range andvariance analysis shows that the primary and secondary factors influence the removal ofTN as follows: mixed liquor reflux ratio> dissolved oxygen> sludge reflux ratio. Themeasured and simulation results show that the mixture reflux ratio influence theremoval of TN of A2/O process is significant, highly significant, respectively, but thetrend of the measured and simulated values are similar. In order to reduce the value ofeffluent TN as the goal in rainwater shock loads period, considering the economic andeffluent quality to get the optimum combination as follows: mixed liquor reflux ratio,sludge recycle ratio, dissolved oxygen concentration were200%,100%,1~2mg/L,respectively.The results showed that total nitrogen removal efficiency can be improved byadjusting the mixed liquor reflux ratio, sludge reflux ratio and dissolved oxygen inrainwater shock loads period of WWTP. However, this adjustment strategy will need toconsider influent water quality and quantity of real-time situation, combined withaeration equipment and reflow equipment regulation range of WWTP, adjustedoperating parameters to obtain effective regulation runs. Mathematical model can’trepresent the WWTP entirely. Inspection and correction of mathematical models andmodel parameters need to use actual operation results of WWTP, but to some extent thesimulation results can predict the measured results and provide a clear direction for future experiments.