Fortunately for the current residents of the city that was home to Mozart, Beethoven and Sigmund Freud, the E_OS (Energy Optimization through Sludge Treatment) project has now delivered a plant that not only processes up to 1’000 cubic meters of wastewater per minute, but also produces around 78 GWh of electricity and 82 GWh of heat from biogas. The facility is now fully self-sufficient from an energy point of view and has thereby reduced Vienna’s annual carbon emissions by 40’000 tonnes.

The Sulzer team that worked closely with the project engineers have in-fact helped transform a large wastewater treatment plant from a major energy consumer into a sustainable green energy producer.

Due to its decades of experience in water and wastewater treatment applications, Sulzer was able to specify, supply and install smart process solutions to help reduce energy consumption and improve equipment reliability at the facility.

Getting into the mix

The old wastewater treatment plant was using more than 1% of the all the electricity produced by Vienna's largest energy provider. Not ideal from either a cost or an efficiency point of view!

The first of those solutions were the mixer units for six 30-meter-high digester tanks, each capable of generating large quantities of biogas.

The giant mixers continually stir the sludge in the tanks to keep the biogas production process running optimally. Sulzer’s solution involved the use of a large diameter Scaba vertical agitator, rotating at a low speed. This would ensure smaller motors were required to power the process, unlocking energy savings.

When the first unit was installed on site, tests conducted by the Vienna University of Technology ensured that this efficient configuration met the facility’s performance needs.

During the water treatment process, air oxygenates the water through an array of fine-bubble diffusers. In conversations with the project team, Sulzer’s engineers learned that their planned air supply configuration used three large 1.2 MW compressors. However, after assessing the flow and pressure requirements, Sulzer suggested that the required output could be delivered by balancing the load on eight smaller 400 kW HST turbocompressors. This cut total power consumption by 400 kW, with the rugged HST compressors also offering reduced noise and very low maintenance costs.