Development Of Monitoring And Control System For Wastewater Treatment Based On PLC

The recent years have seen the accelerated industrialization,urbanization and agricultural modernization in China producing quantities of domestic wastewater and industrial wastewater.Direct emissions of wastewater lead to serious problems such as water pollution,ecological balance destruction in water,as well as the shortage of water resource day by day.It puts forward a higher requirement to wastewater treatment plants by the pressing needs of the wastewater treatment and the national laws.Wastewater treatment plants can improve the automation degree of wastewater treatment system,improve the quality of wastewater treatment,and save the cost of manpower and resources by introducing the monitoring and control system,which has important practical significance and economic value.According to the actual demand of Daqing Xicheng District Wastewater Treatment Plant,this dissertation developed a set of monitoring and control system based on PLC and touch screen,on the basis of the original equipment and instruments.The wastewater treatment process as well as main equipment and instruments in the wastewater treatment plant was analyzed.The design principles and the function of the monitoring and control system were made out.One monitoring and control system constructed by a three-level monitoring and control network,which consists of a central monitoring and control room,distributed PLC control stations,the equipment and instruments,was defined.The Schneider Quantum 140 series PLC was chosen,and the Schneider Magelis XBTGT series graphics terminal(touch screen)was selected as the upper machine.Then the site layout of the PLC stations was determined according to the actual situation of the plant.The equipment composition and the function of the central monitoring and control room were analyzed and determined.Fiber industrial Ethernet was selected to construct the communication system after analyzing.The overall scheme of the monitoring and control system was eventually formed.The monitoring and control function of each PLC station was analyzed according the main equipment and instruments it is responsible for.The specific models of the PLC were determined according to the input and output points and the storage capacity,as well as the related functional PLC modules.Necessary electrical equipment was also determined,with which the electrical installation wiring scheme of each station was formed.For the core technology in the process of aeration biological filter,fuzzy PID control method was applied to establish the control strategy on account of its uncertainty,nonlinearity and time-variability.The monitoring and control system in wastewater treatment plant in Daqing Xicheng District has been put into operation and it works well and achieves the desired monitoring and control purposes.