Application Of Fuzzy PID Controller In Aeration Tank Of Sewage Treatment Plant

With the growth of global economy and the improvement of our living standards, the discharge capacity of domestic and industrial sewage are increasing, and limited water resources have been polluted in varying degrees. Thus, it is urgent for us to prevent water pollution and protect the water environment. One of the most important measures is to improve the technique of sewage treatment.This paper takes the fourth sewage treatment plant of Xi'an as an example. To solve the problems that the control of aeration rate can be only adjusted on the basis of human experience, a fuzzy PID control algorithm is applied to aeration control system. Based on the dissolved oxygen concentration, this algorithm regulates the amount of incoming air flow rate of blower and changes the dissolved oxygen concentration in the pool by controlling the opening size of aeration valve in bioreactor aeration. Then our algorithm can ensure the organic pollutants in waste water furthest gradated by microorganism and make the effluent in line meet national standards. Firstly, this paper analyzed the function and technique of diffused aeration system. By analyzing the relationship between aeration rate and dissolved oxygen concentration and comparing several test parameters in the progression of sewage treatment, dissolved oxygen value is taken as the control of aeration rate. Secondly,according to the material balance formula,we constructed a mathematical model of aeration control system and proposed control schemes to regulate the aeration valve. Through a simulation comparison in MATLAB, we analyzed the merits and drawbacks of different kinds of control strategies in terms of rapidity, interference immunity and robustness. Results showed that some defects existed in the strategies simply using PID control or fuzzy control.While adopting fuzzy PID controller to control the opening degree of aerator value, we can improve the system with preferable noise immunity and robustness. So we choose fuzzy PID as our control strategy in this paper. At last, we used the Siemens S7-300 PLC as our hardware core of Aeration control system and adopted WIN CC host computer to monitor the entire system. By querying the off-line fuzzy control table, our software part completed theoperation of fuzzy PID control algorithm in PLC.System debugging results demonstrate that the overshoot of system and the variation range of the dissolved oxygen are decreased effectively by using fuzzy PID control to regulate the openning of aeration value. Fuzzy PID controller successfully avoided unstable dissolved oxygen concentration due to human factor, so that the control of valve opening will be found and the performance of control system can be improved.