Vienna's Wastewater Treatment Plant

Every second, 6,000 litres of wastewater enter the Vienna's wastewater treatment plant, which is operated by ebswien, 24 hours a day, 365 days a year. The entire, highly sophisticated cleaning process that follows takes 20 hours. Firstly, wastewater passes through four stages of mechanical cleaning. The plant's biological purification is modelled on nature. Just as in streams and rivers, the wastewater treatment plant's aeration tanks are filled with countless microorganisms which cause the pollutants to decompose. However, inside these gigantic basins, everything happens on a much bigger scale; it is faster, more intense and highly concentrated. This sophisticated level of wastewater treatment requires enormous amounts of energy. The plant consumes more than 60 gigawatt hours of electricity per year - the same amount as 25,000 Viennese households. Most of this electricity is needed to supply the microorganisms with oxygen. As an environmental service provider, ebswien actively pursues every opportunity to generate electricity and heat from renewable energy sources. Our main focus is on the "residual product" of wastewater treatment - Sewage sludge. Heated to 38 degrees Celsius thickened sludge is fed into massive digesters, where it remains for 25 days on average, deprived of any oxygen. The result is sewer gas, of which around 60% is precious, energy-rich methane. In cogeneration units huge engines use this sewer gas as their fuel and generators convert the movement of the cylinders into electrical energy. Much of the electricity produced is used by Vienna's wastewater treatment plant itself. The waste heat from the engines is used to sustainably heat and cool our on-site buildings, but above all it is used to heat the sewage sludge. All surpluses of eco-heat and eco-electricity, are fed into the city grids. By generating more green energy than it consumes for wastewater treatment, our plant is a true "eco-power plant". The service we provide is a vital contribution to the effort of the city of Vienna to achieve its ambitious goal of carbon neutrality by 2040. Vienna's wastewater treatment plant produces both clean wastewater and clean energy; protecting our environment and preserving our climate in challenging times.