By bringing together the water and energy sectors, KoNexus explores new ways to make infrastructure more sustainable and resilient. The project demonstrates how wastewater treatment plants can convert surplus renewable electricity into green gases while making use of oxygen and waste heat to improve wastewater treatment processes.

The energy sector needs to make flexible use of electricity generated from wind and solar power and provide suitable storage options. At the same time, the water sector must adapt its facilities to climate change, demographic changes and increasingly stringent wastewater treatment requirements. KoNexus brings these two perspectives together.

At the heart of the project is a simple idea: wastewater treatment plants are more than just facilities for treating wastewater. They have access to water streams, heat demand, sewage gas, technical infrastructure and, increasingly, their own renewable energy sources. These conditions make them ideal locations for converting surplus renewable electricity into green gases while simultaneously making direct use of by-products.

KoNexus investigates and demonstrates the combined use of Power-to-Gas technologies at wastewater treatment plants.

• Surplus electricity from wind power or photovoltaics is used to produce green hydrogen from water via electrolysis. The hydrogen can either be used directly or further converted into biomethane by adding biogenic carbon dioxide from sewage gas.
• Oxygen produced as a by-product of electrolysis can be used for ozonation or aeration in wastewater treatment.
• Waste heat can be supplied directly to processes at the wastewater treatment plant, reducing the need for additional heat generation.

Through real-world case studies, the project demonstrates how these components interact from a technical, economic and environmental perspective.

• At the Berliner Wasserbetriebe wastewater treatment plant in Schönerlinde, existing components such as electrolysis, methanation, gas storage, oxygen utilisation and ozonation are being integrated into an automated demonstration operation.
• In Cottbus, GICON, together with the Technical University of Munich, is further developing a non-pressurised trickle-bed reactor for biomethanation.
• In Eberswalde, Barnimer Energiebeteiligungsgesellschaft operates a large-scale 1 MW electrolyser and is investigating synergies with a nearby wastewater treatment plant, particularly with regard to the use of oxygen and treated wastewater effluent.

KoNexus therefore pursues a broader vision: the water and energy sectors should increasingly coordinate their investments, data, material flows and infrastructure. Wastewater treatment plants can develop into flexible hubs within a climate-friendly energy system while at the same time making their own wastewater treatment processes more efficient and resilient.

Kompetenzzentrum Wasser Berlin (KWB) coordinates the overall KoNexus project and is also responsible for key scientific and knowledge-transfer activities at the interface between the water and energy sectors:

• Analysis and classification of data types, as well as assessment of risks and potential conflicts of interest associated with data sharing between critical infrastructure operators
• Investigation of the use of electrolyser-generated oxygen in ozonation
• Optimisation of the treatment of wastewater treatment plant effluent for use as feedwater in electrolysers
• Environmental and economic assessment of feedwater treatment compared with the use of drinking water
• Preparation of life cycle assessments to evaluate the sustainability and climate protection benefits of the investigated Power-to-Gas concepts

The results of KoNexus will contribute to the development of a practical guideline for secure data exchange between water and energy operators, taking into account the requirements applicable to critical infrastructure under KRITIS and NIS2. They will also support the planning and operation of Power-to-Gas concepts at wastewater treatment plants. By extrapolating the project results to suitable wastewater treatment plant locations across Germany, the project will estimate the national potential for supporting the energy transition, climate protection and energy neutrality in line with the requirements of the EU Urban Wastewater Treatment Directive.

The project results will be incorporated into national expert committees and technical standards, including those of DWA, DVGW and VDI. National and international exchange of experience with operators and industry experts, including stakeholders from Paris and Copenhagen, will help accelerate the dissemination and acceptance of Power-to-Gas concepts at wastewater treatment plants.