Future
Climate
Environment

Sludge digesters were previously mainly used for stabilising and reducing sewage sludge, a “by-product” of wastewater treatment. The energy recovered during this process was more or less a "pleasant side effect". The initial focus of the E_OS project therefore was to maximise energy recovery. In collaboration with the Institute for Water Quality, Resource and Water Management at the Vienna University of Technology, ebswien hauptkläranlage developed an innovative process. Before the sludge enters the digester, it needs to be dewatered. The "thicker" the sludge, the more energy can be recovered. This rationale is based on the understanding that in order to be digested, the sludge as well as the water it contains need to be heated. If the water content is low, this will save energy. On the other hand, the sludge must not become too "thick" so it can still be pumped through the system. Comprehensive test series in the E_OS pilot plant have impressively confirmed our assumptions that ebswien is able to operate the new digesters using sludge with the double solids content than usual. This shows that smart ideas definitely help to produce more energy!

Thanks to the E_OS project, ebswien progresses from a major energy consumer to an energy-positive wastewater treatment plant. Over a one-year period, the plant is capable of producing more energy (especially electricity) than is needed for wastewater treatment (see diagram below). This significantly improves Vienna's climate footprint: CO₂ equivalent emission goes down by approximately 40,000 tonnes annually, an amount produced when circling the globe by car 6,700 times!