Renewable Energy from Wastewater – Wastewater Treatment Plants as Local Energy Cells

The investigations conducted confirmed the technical feasibility of the selected implementation scenario. In summer, the entire heat demand of a housing estate can be covered with heat from the wastewater treatment plant and in winter, at least 50 % of it can still be covered. This gives great support to the public utility company Kapfenberg (energy supplier) in attaining the goal of a sustainable and CO₂-free heat supply for the development area considered.

The wastewater treatment plant as a local energy cell can make a significant contribution to the energy transition and can thus play an essential role in a sustainable energy supply of the future. This is because wastewater represents a renewable, constant and reliable heat source. By tapping this previously widely unused heat potential, the use of wastewater for energy also contributes to an increase in local energy efficiency and resilience. In terms of economic feasibility, the financial risk associated with the implementation of the presented approach appears to be justifiable in any case, since both the heat supply at the wastewater treatment plant and the heat demand in the housing estate can be regarded as permanent (the heat consumers are at the same time wastewater producers and thus provide a continuous supply of resources).

From the point of view of climate protection, through the planned activation and more targeted use of the existing heat potentials at the wastewater treatment plant, over 37,000 m³ of fossil natural gas can be saved per year, which corresponds to a CO₂ equivalent of around 100t (including the upstream chain). If, in addition, the heat pump is operated with renewable green energy, no new greenhouse gas emissions are generated during the operating phase

Additionally, this project has not only an environmental impact but also an economic one, since the use of wastewater as a renewable and constant local source of energy further decreases energy dependence. It relieves the burden on biomass, which will also play an increasing role in the fossil-free energy future, and it constitutes a surplus of energy to be sold, providing additional income for the water board.

The heat potential in the wastewater treatment plant’s effluent is still far from being fully exhausted. This provides interesting opportunities for further applications. The use of the available heat is not only limited to classic functions such as heating living spaces or commercial facilities, and providing hot water. Potential heat consumers can also be found in agriculture, livestock, and forestry (e.g. heating greenhouses, stables, aquaculture, drying hay, herbs and wood chips). Such purposes would also help to increase local revenues, reduce imports and create jobs.