Applications of PLC in Wastewater Treatment Engineering

To ensure that wastewater is treated effectively and meets regulatory standards, many industrial facilities, such as breweries and chemical plants, incorporate wastewater treatment systems. For example, a large-scale wastewater treatment plant covering 350 square meters, with a treatment capacity of 950 m³/day, might use a Programmable Logic Controller (PLC) for process control. This type of system primarily processes domestic wastewater and small amounts of industrial effluents. Typical chemical oxygen demand (COD) and biochemical oxygen demand (BOD) concentrations are 320 mg/L and 240 mg/L, respectively, which are reduced to 90 mg/L and 50 mg/L after treatment to meet secondary discharge standards. By employing a PLC-based control system, the plant can achieve fully automated operation.

The wastewater treatment plant’s control system is centered around a Programmable Logic Controller (PLC), known for its high automation, flexible programming, robust anti-interference capabilities, and ease of maintenance. The system includes a centralized control room, where all equipment can be managed. Additionally, each unit has its own local control box, used mainly during equipment commissioning and maintenance. This setup allows the system to operate in either a centralized or decentralized mode.

The grate well unit is equipped with essential devices such as the grate well lift pump, float level controller, coarse grate, and float level transmitter, which collectively work to remove particles and suspended solids from the wastewater. The float level transmitter detects the liquid level differential before and after the coarse grate. When this difference exceeds 10 cm, the coarse grate is activated to filter out solids.

The biochemical tank is equipped with devices such as blowers, a dissolved oxygen detector, motorized butterfly valves, a biochemical tank lift pump, and a float level controller, all of which reduce COD and BOD levels in the wastewater.

The biochemical tank operates automatically when the control panel switch is set to the “automatic” mode. The PLC receives analog signals from the dissolved oxygen sensor, which are then processed and compared with preset values. If the dissolved oxygen concentration in the wastewater falls below 0.5 mg/L, the motorized butterfly valve opens, and the blower activates to initiate aeration. Once the oxygen concentration exceeds 2.5 mg/L, the blower stops, and the butterfly valve closes, completing the aeration cycle.

The wastewater station uses a motorized butterfly valve manufactured by a specialized valve control company. This valve can be operated both manually and automatically through the PLC. The dissolved oxygen detector, manufactured by a German company, reliably measures the oxygen concentration in the wastewater. Its high accuracy and 4–20 mA analog output terminals allow it to connect directly to the PLC’s analog input module, ensuring precise oxygen monitoring.

The integration of PLC technology in wastewater treatment enables high levels of automation, precision control, and efficient monitoring across different processing units. By utilizing PLCs, wastewater plants can enhance operational efficiency, ensure compliance with environmental standards, and reduce the labor required for maintenance and monitoring.

Xi'an CHIWATEC A Water Treatment Technology é uma empresa de alta tecnologia especializada em vários dispositivos de processamento de água. Além desses produtos individuais, que abrangem vários tipos e séries, também podemos ajudar com projetos de engenharia abrangentes relacionados. Graças ao nosso trabalho árduo e dedicação desde a nossa fundação, somos agora um dos fabricantes de equipamentos de tratamento de água com desenvolvimento mais rápido na China Ocidental.

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