Wastewater treatment plant modernises rain overflow basins

Warendorf is a town in western Germany and the capital of the Warendorf District. The town is best known today for its well-preserved medieval town centre, horseriding and the opportunities provided for cycling. The Warendorf wastewater treatment system includes two wastewater treatment plants, several pumping stations and special facilities, such as rain overflow basins and rainwater spillways.

To increase system efficiency, the Warendorf wastewater treatment plant operator regularly modernises and equips the system with the latest technologies. As a part of the latest retrofit measures, the decentralised rain overflow basins in the Hoetmar district of Warendorf were coupled directly to the network, the local emergency power generators were replaced and the automation level was updated. The utility has two augers with a maximum conveying capacity of 6500 cubic metres and a basin volume of around 1000 cubic metres. The rain overflow basin is located upstream of a small, decentralised wastewater treatment plant.

As a part of the modernisation program, a PLC based on PLCnext Technology from Phoenix Contact was installed in the automation level. The protocols supported by the AXC F 2152 device, such as OPC UA, and the integrated security functions, were significant reasons for selecting this controller. As the core element of the local automation of the rain overflow basins, it needs to support a variety of protocols. For example, classic fieldbus systems such as Modbus/RTU and Modbus/TCP can read and process the data from the frequency converter, the various measuring devices and the new generator. Additional interfaces, such as Profinet and OPC UA, make it easier to integrate sensors and actuators in the future.

The OPC UA server installed in the AXC F 2152 controller provides the local user interface with information, so wastewater treatment plant employees have all the relevant data available at a glance, displaying the plant’s current status and allowing the employees to control the plants manually.

In the past, key system data was transmitted to the control system via the classic IEC 60870-5-104 remote control protocol. Now it is transmitted to the control system via the OPC UA protocol, offering simple implementation and flexibility, and opening up significant advantages for the operator.

The application is programmed based on the IEC 61131 standard. Using Phoenix Contact’s PLCnext Engineer software functions and program parts already in use could be adopted from the existing system and quickly adapted to the rain overflow basin’s special requirements. The operator can also configure, diagnose and visualise the entire system with this software. As a result, the wastewater treatment plant employees only have to be familiar with one tool to perform all tasks.

The scalability of PLCnext Technology means that the open control platform can be used on multiple PLC performance classes while still behaving and operating in the same way. This allows the operator to use a lower-performance controller for small, decentralised facilities, and equip complex processes with a powerful controller.

From a cybersecurity standpoint, the Warendorf wastewater treatment operation has developed and put into practice a system-wide IT security concept. For example, the individual system parts are already segmented and protected upstream by an FL mGuard security router and firewall. The AXC F 2152 PLC device fits into this IT security concept because it is already equipped with such key functions as an integrated firewall and user administration function.

The firewall installed in the controller limits and monitors the controller connections based on specific rules, while the user administration function allows all user rights to be set up and changed individually. In addition a VPN function means the PLC device can be connected directly and securely to the central infrastructure via the VPN tunnel.

“Modernising the rain overflow basin and the associated new automation technology has created the perfect foundation for solving future challenges,” said Frank Linning, manager of the wastewater treatment plants and special facilities at the Warendorf wastewater operation. “In particular, the IT security functions available in PLCnext Technology and its support for OPC UA communications make it a perfect fit for our automation philosophy.”

The demands and framework conditions in water management systems are changing faster than ever. To optimise their processes, wastewater systems need to record and process more data and information than ever before. The foundation for this is a flexible and open automation technology that also supports future standards, is easy for employees to use and truly supports them in their everyday work.