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News | 2020-05-26
Henriksdal sewage treatment facility

After the reconstruction, Henriksdal will become Sweden´s largest sewage treatment facility. Photo: Mikael Ullén/Stockholm Vatten och Avfall

Digital twin secures commissioning of new Stockholm sewage works

Summer 2020 will see the installation of a revolutionary new treatment process at the Henriksdal sewage treatment facility in Stockholm. The implementation schedule is tight – full purification is required around the clock, even during reconstruction, so there is little room for mistakes and delays. To ensure that the new process will work optimally right from the start, Stockholm Vatten och Avfall will deploy a digital twin developed by IVL and Siemens.

"Having a digital copy of the process is advantageous in many ways. For example, we are able to test and trim the system in advance and thus are better prepared to deal with any disruptions that may affect the purification rate," says Erik U. Lindblom, Project Manager at IVL Swedish Environmental Research Institute.

After the major reconstruction now underway, Henriksdal will become Sweden´s largest treatment facility. Anchored in the bedrock in southern Stockholm, it will have the capacity to purify wastewater generated by 1.6 million people. It will be able to cope with Stockholm’s growing population and simultaneously reduce emissions of eutrophic matter into the Baltic Sea.

The pollution load in incoming wastewater varies significantly over the day, which is a major challenge for sewage facilities. When it rains, the inflow can be four times higher than normal, and during snow melting the temperature of the water drops, which impairs bacterial ability to purify wastewater in the biological treatment stage.

To manage these fluctuations, the plant is overseen by an advanced process control system. Much is automated, but the system still requires proper handling and hundreds of controllers and thousands of signals must be fine-tuned. If errors are not discovered prior to commissioning they can be both difficult and time-consuming to troubleshoot and rectify. This can also lead to unwanted emissions to the aquatic environment. To ensure that the operation functions optimally right from the very start, IVL together with Stockholm Vatten och Avfall and Siemens has developed a digital process twin to evaluate and tune process control in advance. The project is called VAT – Virtual Acceptance Test. It is implemented by combining Siemens process control system PCS7 with dynamic Matlab / Simulink software mathematical models that can simulate both purification outcomes and the real-time consumption of resources.

"By deploying a digital twin, we are able to test and verify the new control system before it becomes operational," says Erik U. Lindblom.

Better preparedness for extreme weather

In addition to tuning the control systems and correcting errors, the digital twin can also be used to gauge performance under conditions difficult to generate in reality. Here we test whether we will be able to cope with events that may not happen that often, but which are important from an environmental perspective and may have a significant impact on society at large. For example, we need to be equipped to deal with heavy downpours that may cause our cities to flood. What is today defined as centenary rainfall, a term that denotes extreme precipitation events that statistically occur only once every 100 years, is forecasted to happen more often in the future and to be even more devastating.

"One important goal is to allow operational personnel and other project participants to practice and train with the new control system environment using a virtual digital process copy. We believe this will lead to faster deployment and fewer problems, and also prepare us for dealing with operational disruptions and extreme weather conditions – something we expect will become even more frequent," says Oscar Samuelsson at IVL, who is also engaged in the project.

For more information, please contact:
Erik U. Lindblom, erik.u.lindblom@ivl.se, +46 (0)10-788 69 42
Oscar Samuelsson, oscar.samuelsson@ivl.se, +46 (0)10-788 66 64
Robert Wallin, robert.wallin@siemens.com, +46 (0)8-728 12 59

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