Wastewater as a power plant: Electrical energy from the sewage treatment plant
Today’s sewage treatment plants operate according to the energy-intensive cleaning principle of the “activated sludge process”. Here, wastewater pollutants are oxidized to carbon dioxide by microorganisms with the addition of oxygen and rendered harmless. However, the energy potential of the wastewater is also almost completely lost. In Europe, around 1600 gigawatt hours of electricity are used annually for this cleaning process. After all, this is the annual energy production of two large power plants with an output of 1000 MW.
In order to prove that sewage treatment plants can be not only energy destroyers but also energy producers, the Kompetenzzentrum Wasser Berlin (KWB) together with 15 European partners from industry and research carried out the 3-year research project POWERSTEP.
The scientists tested various technical approaches to generating more electrical energy from the wastewater treatment plants than they consume. According to the consideration, the organic substances contained in the wastewater contain so much chemical energy that, using innovative technologies, the energy previously required for the purification process could be completely compensated and even an excess could be achieved.
In the most successful case study in the Powerstep process, the scientists removed the high-energy organic substances at the inlet to the sewage treatment plant. They were fed directly into a biogas production plant. The biogas, in turn, was used to generate electrical energy – thus the scientists proved that the principle works.
Together with other innovative components such as power-to-gas, heat-to-power and nutrient recovery, they developed an overall concept for a future wastewater treatment plant that makes optimum use of the existing resources in the wastewater. The operating costs of the wastewater treatment plant remain within the limits customary today, and the treatment performance of the wastewater treatment plant is not impaired either. With this innovative approach as a prime example of a “green economy”, municipalities are thus given a further lever to achieve the ambitious climate targets for 2030-2050.
The scientists calculated that the future energy potential could amount to 87500 Gigawatt hours per year – quite an impressive figure.