Research On The Aeration Control System Of Cyclic Activated Sludge Sewage Treatment

With the development of the society and the increase of the population, the problem of water pollution becomes more and more serious. Nowadays, sewage treatment plays an important role. Because of the high energy consumption, sewage treatment is very costly. The aeration system account for 40%～50% of the total energy consumption. Therefore, the subject about energy reducing in aeration system catches more and more attention in the area of process control industry.The metabolism of activated sludge (microbial populations) is applied to consume organic matter in cyclic activated sludge sewage treatment. Due to the complexity of internal mechanism and slow response of control action, the control of aeration process is highly demanding and difficult. This thesis has been carried out based on a real sewage treatment plant. Firstly, I introduce the significance of aeration control from the aspects of economic indicators and quality indicators. Based on studying the aeration control system, I chose dissolved oxygen as the control parameter of the aeration system. At the same time, I analyze the energy saving effect of using blowers as the actuator instead of using butterfly valve, and design the aeration control plan according to actual conditions. Based on the material balance equation, I analyze the main factors which influence the dissolved oxygen concentration, then establish aeration control object model by analyzing the process of microbial metabolism and dissolved oxygen. According to the characteristics of the aeration process, I propose the simplifying condition of the model. Due to the time-varying characteristics of the controlled object and difficult online identification of the parameters, I introduce fuzzy PID controller in aeration process. Fuzzy PID controller can adjust the PID controller parameters according to the changes of the model of controlled object to improve the robustness of the system, increase the controllability of aeration system and achieve better control effect.Finally, I analyze the control performance of the Fuzzy PID control system designed in the thesis by simulation. The Fuzzy PID control system in this paper not only has better tracking and strong anti-disturbance performance, but also can adapt to parameters changes better, so it is quite effective in the aeration control system.