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



Policy areas

Organisation name Wasserverband Mürzverband

Share this article via:

Contact person: Dr. Florian Kretschmer, Project partner

The supply of heating and hot water implies large amounts of energy, which to date come mostly from fossil sources. To counteract climate change and pursue the decarbonisation of cities, renewable heat sources such as wastewater have been increasingly coming into focus in recent years. Wastewater contains large amounts of chemicals and thermal energy, and is produced wherever human activities take place; this means that it is not only a renewable but also a constant and reliable source of energy and heat.

This project, starting from the Kapfenberg wastewater treatment plant, investigated possible innovative approaches on whether and how energy (heat) recovery from wastewater could contribute to the public heating supply.

So far, the only energy-related aim of wastewater treatment plants has been self-sufficiency but usually, the energy produced by this type of plant may far exceed its self-supply needs. Consequently, a wastewater treatment plant could also be re-imagined and developed as a local energy/heat cell and this is possible with the same kind of plants across Europe, making the heating and hot water supply local, climate-friendly, renewable and sustainable.

The investigations confirmed the technical feasibility of the selected implementation scenario. It can develop both available heat sources at the wastewater treatment plant, therefore it satisfies two types of heat demand – the wastewater treatment plant’s internal demand, and external demands.

Consequently, the project supports the exploitation of what is so far an unused heat potential (the wastewater heat from the wastewater treatment plant’s effluent), and the more efficient use of the available energy sources. Wastewater heat specifically used for internal low-temperature applications (e.g. digester heating) makes the high energy from the sewage gas/biogas combustion available for other, external uses.

The wastewater treatment plant as a local, renewable and reliable energy/heat cell represents a key element for the ongoing intent of an energetic transition and can thus play an essential role in the sustainable energy supply of the future.

The research partners in the project consortium have the opportunity to bring theoretic knowledge into practice and to establish a showcase of a novel approach for integrated wastewater and energy planning. The practical application will further serve as a demonstration site for interested stakeholders from other municipalities and it will provide practical experience (and operational data) to optimise future implementations. Finally, the public workshop with residents of the area revealed that, nowadays, the majority of people strongly appreciate a local, climate-friendly and sustainable energy supply for their homes.

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.

Also interesting