Numerical Simulation And Nitrogen Removal Optimization In Plug-flow A~2O Process

In order to improve the problem of co-treatment of domestic wastewater and landfill leachate, a plug-flow A~2O process which was widely used in wastewater treatment feild in our country was investigated in this paper. After analyzing the characteristics of the influent, process feature and operating condition, we used numerical simulation based on activated sludge model ASM2 d to built the mathematic model of plug-flow A~2O process. Then we ensured the accuracy of the model with the help of analyzing the sensitivity of parameters and calibrating the parameters. With this model, we simulated the effect of internal return ratio, sludge return ratio and the concentration of dissolved oxygen in the aerobic tank in different level, the operating optimization scheme was proposed.According to the plug-flow feature and the requirement of multi-mode operation,the mathematical models of modified plug-flow A~2O process were then built with ASM2 d as simulation mechanism and GPS-X software as simulation platform. The reactor construction plan was used in static simulation and the result was uesd for analyzing the sensitivity of all the chemometrics and kinetic parameters. Combined these results and literature, we calibrated the parametersAUTm(autotrophic maximum specific growth rate)from 1d-1 to 0.8d-1. After calibrating the parameters and applying the actual water quality and quantity of the wastewater treatment plant to the model for dynamic simulation, the relative errors between the simulated results of COD, TN and NH4+-N of the effluent and the measured value turned out to be 2.1%, 2.6% and1.6% respectively. The results showed that the model could simulate the operation of WWTP well after calibrating the parameters.The main factors that affect the treatment of A~2O process are internal return ratio,sludge return ratio and the concentration of dissolved oxygen in the aerobic tank and all these factors are easy to control. Using the single factor experiment and the multi-factor orthogonal experiment to simulate the effect on nitrogen removal of internal return ratio, sludge return ratio and the concentration of dissolved oxygen in the aerobic tank in different level, respectively. The results showed that the optimum removal efficiency appears with an internal return ratio of 400%, sludge return ratio of 100% and the concentration of dissolved oxygen in aerobic tank of 3mg/L.Meanwhile the effluent concentration could steadily reached the discharge standard ofpollutants for municipal wastewater treatment plant A-level standard.