Open Access

Kevin Kramer

• The annual wastewater flow that is treated by public wastewater treatment plants in Germany amounts to approx. 10 ∗ 10^9 m3/a and forms an ”artificial” hydropower potential that can be used for energy generation or recovery. In the context of this paper, energy recovery in the outlet of wastewater treatment plants is examined using the specific example of the water wheel at the Warendorf central wastewater treatment plant. The ”artificial” hydropower potential can be roughly estimated at up to 20 to 105 GWh/a , whereby this is largely dependent on the hydraulic gradient. The strong variance results, among other things, from the findings of the water wheel operation in Warendorf. The decisive aspect here is the differential factor, which describes the deviation between the theoretical and actual energy yield of the water wheel. The factor includes maintenance work, downtimes and insufficient inflows, which are associated with a loss of output. In the case study, the annual energy recovery amounts to approx. 2 % of the annual electricity consumption of the wastewater treatment plant and can be estimated to 23,500 kWh (2022). In the context of the economic analysis, it can be seen that despite the ”low” yield, economic operation is possible if the system is viewed as a long-term investment - payback period of the example is approx. 14,5 years. The 27-year operation (1996 - 2023) of the water wheel at the Warendorf central wastewater treatment plant confirms this and important findings on successful practical operation can be shown in the context of this paper.