The power of wastewater is underestimated; household wastewater contains a lot of organic matter that can be transformed into valuable renewable energy. To exploit this potential, the POWERSTEP project converted sewage treatment plants into power facilities, while still achieving high quality water treatment.
Nearly 1% of the EU‘s electricity demand is consumed by wastewater treatment plants. POWERSTEP achieved an energy-neutral or even energy-positive wastewater treatment plant based on a combination of new concepts and optimized integration of available technologies, such as sewage sludge digestion and biogas valorization, at its six large-scale demonstration sites in Germany, Sweden, Denmark, Austria and Switzerland. REVOLVE had the chance to interview two of the project’s coordinators, Christian Remy and Christian Loderer, from the Berlin Centre of Competence for Water, to learn more about POWERSTEP and capitalizing on this untapped renewable source. Project Manager, Berlin Centre of Competence for Water
How does POWERSTEP generate energy from wastewater?
Christian Remy: In POWERSTEP, as energy is mainly generated by biogas production from the organic matter in sewage sludge, a digester is a key element. Larger wastewater treatment plants typically have an anaerobic digestion stage where part of the sewage sludge is converted into biogas (CH4 and CO2). However, a large portion of the energy potential is simply lost in these plants as carbon is converted into CO2 in the cleaning process. By using the new concepts tested in POWERSTEP, this biogas output can be increased up to 80-150% by redirecting more of the organic matter into the digestion process. If conditions are good and the concept is fully optimized, the wastewater treatment plant can even produce more energy than it consumes, making it an energy-positive water treatment system that can deliver energy to other consumers!
Why is making Waste Water Treatment Plants (WWTPs) energy neutral or energy positive an important step for the industry?
Christian Loderer: Although WWTPs only consume around 1% of electricity demand, they are still the largest public consumer of a city, making them relevant for the POWERSTEP concept. Operational costs for wastewater treatment mainly originate from energy use, a cost that can be significantly reduced if more energy is exploited from the wastewater. It only makes sense to think about optimizing this process, which also results in reducing your wastewater treatment fees. An additional benefit of optimizing the wastewater treatment process is also the long-term effect for the environment, such as the reduction of greenhouse gas emissions in your municipality. All of this creates a more sustainable environment for future generations.
How is the energy created by the POWERSTEP technology integrated in the energy network?
Christian Remy: The major form of energy produced in POWERSTEP is in the form of biogas. This can be valorized via different routes: electricity and heat are produced on-site (e.g. in a CHP plant) to cover the demand of the WWTPs internally, or they can be sold to the grid or to near-by customers. Upgrading of biogas and direct injection of this renewable “green” gas into the public gas grid is another form of integrating the WWTPs into the energy network of the future. Biogas can also be converted to a valuable biofuel for green mobility. Finally, WWTPs can also help to stabilize the electricity grid by using power-to-gas approaches or dedicated load management strategies.
Christian Loderer: With biogas as the main energy output, the goal of POWERSTEP was to produce more biogas (energy) than in traditional WWTPs, so new advanced treatment technologies, such as carbon extraction filters at the beginning of the wastewater treatment line were implemented to extract the “energy-rich” sludge to obtain a higher biogas output. Results showed up to an 80% increase of extraction rates using this advanced technology compared to 30% using the classical way.
How does the energy contribute to the stability of the regional energy network?
Christian Remy: WWTPs can play a role in stabilizing the regional energy network if their consumption and production capacity is controlled in cooperation with the grid operator. They have a certain potential to adapt their consumption profile, but also their output of energy to the situation in the grid, adding flexibility to the grid operator to stabilize the network. This “load balancing” feature can even be enhanced by following a power-to-gas approach, converting excess electricity in the network into biogas which can then be valorized in other routes or stored in the grid for future use. For the WWTP operators, this is another option to have extra revenue from the load balancing market, which will further enhance the economic attractiveness of the POWERSTEP concept.
Why is it important that the EU recognizes biogas from sewage as renewable and how do you plan on pushing for the prioritization of sewage biogas?
Christian Loderer: Biogas from sewage treatment plants is already recognized by the EU as a renewable source of energy. However, this perspective is not yet implemented properly in the national rules for taxes, fees and subsidies in the energy sector. Hence, the incentives to follow the POWERSTEP concept could be improved by granting the same support for biogas from WWTPs than to other types of biogas, e.g. from agricultural sources. In fact, biogas from sewage comes without some of the inherent drawbacks of traditional biogas production, such as competition for land use with food production or negative effects of fertilizer and pesticide applications. POWERSTEP formulated a list of key elements of policy support in a policy brief, which should promote the concept and help to pave the regulatory framework for more exploitation of this renewable source of energy.
What are the challenges or opportunities of applying POWERSTEP’s findings to water treatment plants across Europe?
Christian Remy: During the POWERSTEP project, it became clear that many technologies are ready for uptake to improve the future exploitation of the full energy potential contained in wastewater. However, their financial viability depend very much on the national regulatory framework, given that the energy markets are highly regulated by taxes, fees and subsidies in many EU countries. The challenge is now to find a suitable valorization route of the POWERSTEP energy for each country and location which can make the concept economically viable in the long-term. A market survey showed that a lot of potential for improvement can be found in certain countries based on the existing WWTP infrastructure, while other countries are already further developed in energy efficiency of this sector.
Christian Loderer: Opportunities for the POWERSTEP concept can arise specifically in places where aging infrastructure is to be replaced or retrofitted, or if new treatment plants are built. WWTP operators are encouraged to look for new solutions with increased energy efficiency and higher exploitation of the energy potential present in the wastewater, but they also have to be supported by adequate policy frameworks and regulations to make these concepts economically attractive and sustainable. Finally, this approach will help us to keep the good water quality and at the same time improve the sustainability of our treatment plants by drawing on the power of wastewater!