1. Introduction With the rapid development of environmental protection in China, the purification and treatment of industrial wastewater and domestic sewage has become an urgent task. Biological aerated filter technology, which requires less investment and is flexible in operation, has been widely applied. Biological aerated filters are a new technology in wastewater treatment research and experimentation. Research began abroad in the early 20th century, and it was basically finalized by the late 1980s. In recent years, with the development of automation technology, equipment, and online monitoring instruments, the automation of wastewater treatment has become possible. Simultaneously, automated monitoring and real-time control of wastewater treatment processes are key to improving wastewater treatment efficiency, reducing chemical dosage, and lowering energy consumption. Generally, a PLC-based automatic process monitoring system is used to control equipment such as blowers, pumps, and electric valves in real time, as well as reaction time, aeration time and intensity, backwashing time and intensity, etc., to ensure that the water quality meets the national discharge standards. Therefore, wastewater treatment is a complex system with multiple parameters (such as liquid level, water composition, temperature, pressure, and flow rate), multiple tasks (such as wastewater transport, air volume control, backwash water volume control, pump start-up and shutdown), and multiple devices (such as bar screens, pumps, blowers, and valves), exhibiting randomness, time-varying characteristics, and coupling. Thus, wastewater treatment should be modernized and managed by an intelligent monitoring and integrated management system to ensure its safe and reliable operation. 2. Fieldbus Technology In wastewater treatment plants, field control devices are widely distributed. Using traditional control schemes would necessitate laying a large number of control and signal cables, wasting significant manpower and resources, which is highly uneconomical. It also complicates the system and reduces reliability. Adopting the currently popular fieldbus technology can reduce costs while improving system reliability, making the system easier to expand and maintain. Interbus is an international, open fieldbus standard. Currently, most automated manufacturing manufacturers worldwide provide Interbus communication interfaces for their automated equipment. Interbus is a mature technology widely used in manufacturing and process control. Using Interbus bus modules for high-speed data transmission in distributed control systems can replace expensive 24V or 4-20mA parallel signal lines, solve common workshop-level communication tasks, provide large-scale data communication services, and offer medium-speed transmission for medium-level tasks. 3. System Composition and Functional Design Modern wastewater treatment systems require integrated management and control, and automated office operations. The control system not only has good interfaces with lower-level control equipment but also interfaces for integration with upper-level management systems, while also possessing scalability. Therefore, modern wastewater treatment systems require the use of fieldbus or industrial Ethernet technologies at the lower level, and excellent monitoring and configuration software at the upper level. To enhance system reliability and ensure long-term, fault-free operation, redundancy and fault-tolerant technologies are needed. Based on the concept of totally integrated automation, the wastewater treatment plant control system is divided into management level, control level, and field level. 3.1 Management Level The management level is the core of the system, managing and controlling all parts of the wastewater treatment process and achieving plant-level office automation. The management level provides a human-machine interface, serving as the interface for information exchange between the entire control system and the control section. The computers at the management level have inter-communication capabilities, enabling data exchange and sharing. Considering the hierarchical and divisible nature of the management layer's functional structure, a client/server architecture is adopted. A large-scale network relational database is selected for the server, meeting the requirements of open, distributed database management methods. A local area network (LAN) is formed, consisting of the server, management computers, and other station computers. The central monitoring computer and workshop-level field control stations form the plant's industrial control network, completing the monitoring and control of production processes, instruments, and equipment within each workshop. This system uses two industrial computers (operator station and engineer station) manufactured by Advantech as backups for each other, communicating via TCP/IP. 3.2 Control Level The control level is crucial for realizing the system's functions and serves as the hub between the management and field levels. Its main function is to receive parameters or commands from the management layer, control the wastewater treatment production process, and simultaneously transmit field status to the management layer. The controller is the core of the entire system; therefore, the Phoenix Contact ILC350 controller is used in the control level. This controller itself has a TCP/IP communication interface and connects to remote I/O modules through branch modules. The remote distributed I/O modules communicate with field devices and sensors. 3.3 Field Level The field level is the foundation for realizing system functions. It mainly consists of primary instruments and control equipment. Its main functions are to monitor and track the production process, instruments, and equipment within its scope, and to upload the monitored data; it also receives commands from the control level to control the actuators. Distributed configuration means that the controller, remote I/O modules, and field devices are connected via fieldbus signal cables. Each relatively centralized control point is configured with a remote distributed intelligent I/O module (ibs il 24 bk). Field I/O signals are directly input to the I/O module. Each ibs il 24 bk module has two Interbus interfaces. 4 Software Design and Selection 4.1 Upper Computer System Requirements The upper computer system must have the ability to communicate with multiple lower computer systems, monitor the working status of multiple lower computers in real time, display the working curves in the production process; have remote control capabilities; collect data from lower computers, and store, query, display, and print historical data. Therefore, in an automatic monitoring system, the monitoring configuration software in operation is the data collection and processing center, remote monitoring center, and data forwarding center of the system. The monitoring configuration software in operation, together with various control and detection equipment, constitutes a rapid response control center. 4.2 Configuration software selection The Kingview 6.5 configuration software developed by Beijing Yacon Company is selected. The functions and features of this configuration software are: (1) User-friendly human-machine interface, convenient control operation. (2) Real-time screen display function: Generate graphics using design or actual pictures, and display a parameter in real time. The displayed charts include: overall plant plan, overall plant process flow diagram, plan of each structure, dynamic simulation diagram of the main process and equipment status of each part, trend analysis diagram, data bar chart, status table, alarm table, daily report, and monthly report. Data processing: Analyze, statistically analyze, calculate, and display data using online data and data in the database. (3) Alarm function: When a parameter is abnormal or the equipment fails, it can issue alarms such as sound, light, screen, input alarm table, printer output or play pre-recorded voice prompts according to different alarm categories, and display corresponding prompt information and screens at the same time, record in the database, and can be classified by level. (4) Report function: Generate and store annual, monthly, daily reports and operating parameter reports. (5) Printing function: Print various reports, and print various events and alarms in real time. (6) Communication function: This configuration software supports standards such as DDE, OLE, ODBC, OPC and SQL, and can provide multiple ways to exchange data with the upper layer. 4.3 Control software programming The main basis of software programming is to provide control laws for production processes. The same treatment process may have different control strategies. According to the functional division of the sewage treatment plant, it is divided into three functional blocks: automatic dosing control, automatic sludge discharge control of clarifier, and biological aeration filter control. (1) Automatic dosing control: refers to the closed-loop control formed by the online measured water quality parameters and the set parameters. Each clarifier is equipped with two metering pumps, one in operation and one on standby. When any pump fails, the standby pump will automatically start operation. The metering pump is equipped with a frequency converter, which controls the pump stroke and motor speed according to the influent flow rate, influent turbidity, and effluent turbidity signals, thereby achieving the purpose of controlling the dosage. (2) Automatic sludge discharge control of clarifier: refers to adjusting the sludge discharge time and sludge discharge cycle in real time according to the online measured water quality parameters, sludge interface of clarifier and effluent water quality. (3) Control of biological aeration filter: According to the research on the operation control mode of biological aeration filter in recent years, the control of biological aeration filter process can be divided into head loss method and time control method. Among them, head loss is used to control the backwashing of biological aeration filter. When there are multiple aeration tanks, the accuracy of water distribution balance directly affects the backwashing effect. In actual operation, it is difficult to achieve strict water distribution balance in each tank. Therefore, the time control method is generally used in actual engineering cases. And by setting a flexible time adjustment interface through the host computer, it is a good solution to ensure the efficient operation of biological aeration filter. 5. Conclusion The adoption of fieldbus in wastewater treatment control systems has transformed the traditional all-analog transmission method, achieving digital transmission at the fieldbus level. This improves signal transmission accuracy and enhances the flexibility of on-site control. This automatic control system has been put into operation at the wastewater treatment plants of Jiuquan Iron & Steel Group's Yuzhong Steel Plant and Northwest University for Nationalities, achieving significant economic and social benefits.