Research And Design Of The Sewage Treatment Control System

With the rapid economic development of China, the issue of water pollution has become a significant problem which we have to focus on, especially how to deal with the sanitary sewage is the top priority of our daily life. Although the traditional wastewater treatment methods could settle the problem to a certain degree, it also has its side effects. As a result, my research is mainly talk about how to introduce new control methods on the basis of conventional ways to improve these wage treatment.The sewage disposal control system in this paper is constitute of S7-300 PLC CPU315(master station), S7-200 PLC CPU226(slave station), WINCC and TP177 touch screen. At first, the EM235 analog quantity input/output extended module of S7-200 PLC acquire the concentration of dissolved oxygen which detected by dissolved oxygen meter. Then, using the communication module EM277 transfers the data to master station S7-300 PLC. Finally, the self-adaptive fuzzy PID control can be realized by means of the fuzzy reasoning arithmetic. S7-300 PLC sends commands to S7-200 PLC rely on the PROFBUS-DP trunk, the latter responds to the commands which it receives. That is to say, the EM232 analog quantity output extended module export 4~20mA signal to control frequency converter, and then, the revolving speed if roots blower can be modulated by controlling the frequency of frequency converter. As a result, the DO concentration will be controlled precisely in real time, the working status and task execution should also be reported to the upper computer. Eventually we complete the real-time online monitoring of sewage treatment control system.The process of sewage treatment is complex due to the plenty of parameters which reflect the index of water pollution. The usual way is to select the parameter which can judge the quality whether it qualified. However, in this paper, we select the DO concentration which is relatively easy to control as the controlled object. The control system of DO concentration is characteristic of non-linear, large lag and time-varying, these make it difficult to obtain satisfactory control effect using routine PID control in most instances. Therefore, our system introduces a new intelligence algorithm which called fuzzy control algorithm. This algorithm combines with the routine PID control to form a hybrid intelligent controller which means using the self-adaptive fuzzy PID control strategy to control the DO concentration. According to the simulation results and practical application, we conclude that this method could not only reduce the amount of overshoot in the system operation process significantly, but also speed up the response and improve the stability. Meanwhile, it has excellent robustness. Comparing to the routine PID control, one of the most important advantages of the self-adaptive fuzzy PID control is that under the precondition of the basic requirements, the transient time of the dissolved oxygen concentration control system has been greatly shortened. As a consequence, the work efficiency could be improved significantly.