The wastewater treatment plant Bautzen replaced its outdated automation technology with modern AC500 PLCs. To modernize the system, the PLCs were systematically replaced one by one during ongoing operation.
The Abwasserzweckverband (AZV) Bautzen, an association for wastewater treatment, operates the wastewater treatment plant in the Saxon city of Bautzen, Germany. Wastewater and residues from Bautzen’s and the AZV’s decentralized disposal areas are treated here. In 2019, the wastewater treatment plant took a necessary and big step towards modernization: It replaced its outdated distributed control system (DCS) and control technology, the first elements of which had been installed by ABB in 1997 and had been running ever since.
The challenge was to modernize the plant while it remained permanently in operation. All programmable logic controllers (PLCs) had to be updated successively. Autodeltass was hired to replace the control and instrumentation technology: They demounted the old PLCs and replaced them with the new AC500, and they replaced the old DCS, which had served as the operating and monitoring system, with a modern solution.
The AZV Bautzen chose the AC500 automation platform based on their positive experience with the previous ABB PLCs and their reliability. According to Andreas Schulz, project manager for plant engineering at autodeltass, the PLCs’ high compatibility and variety of communication options made switching easy. “When we replaced the control technology step by step, it was still possible to communicate with the old PLCs because the AC500 understood the old protocols. This way, we were able to replace PLC after PLC and keep the treatment plant up and running at all times.”
Step by step replacement
During the replacement, six PLCs were exchanged in three phases. The old and new systems were partially running in parallel during the works, and functions were transferred from the old to the new system successively. Autodeltass exchanged the PLCs subsystem by subsystem and connected them to the DCS.
With the new control technology, the wastewater treatment plant opted for a modern and consistent automation platform. They now have the certainty of being state-of-the-art and being supplied within 24 hours if spare parts are needed. The considerably more powerful AC500 directly displays the current system status via integrated visualization. Thanks to this, system errors can be found and fixed more quickly.
Robert Wolf is the technical division manager and is responsible for the wastewater treatment plant. He played a key role in the modernization and appreciates the fact that the AC500 can be very easily programmed: “The PLCs can be programmed according to the IEC 61131-3 standard using Automation Builder. To us, it’s important to have the programming know-how within our company because we want to be able to troubleshoot and carry out simple programming tasks ourselves. For example, I recently integrated the alarm system into a PLC.”
The ABB Ability™ Operations Data Management software zenon functions as the new system for monitoring and visualizing the subsystems. Zenon is an open and scalable system and offers more and enhanced functionalities compared to the old DCS. It runs on two servers in a modern server-based system, instead of the classical single-location solution. This guarantees a high level of reliability and system availability. Furthermore, using a terminal server makes it possible for members of staff to access the applications from home with their notebooks and to receive error messages to their smartphones.
The wastewater treatment plant Bautzen received new ABB control and automation technology (Image: autodeltass). 
PM583-ETH CPUs belong to the AC500 family and are now in operation at the wastewater treatment plant Bautzen (Image: autodeltass). 
AC500 PLCs
