Wastewater treatment plants as locations for green hydrogen and biomethane

In the KoNexus project, scientists from the Reiner Lemoine Institute (RLI), together with partners, are investigating how wastewater treatment plants can convert surplus electricity from wind and solar energy into green hydrogen and biomethane. To this end, the project team is demonstrating the integrated operation of a power-to-gas (PtG) plant at wastewater treatment plant sites in Eberswalde and Schönerlinden near Berlin. The project results are intended to help evaluate the sector coupling of the water and energy industries technically, economically and ecologically and to develop new business models for the energy transition.

Wastewater treatment plants as part of a climate-neutral energy system

Wastewater treatment plants offer ideal conditions for the production of green gases. They have water for electrolysis, generate sewage gas with biogenic CO₂ and need energy and oxygen for their processes themselves. The project team is using these resources to test the generation, storage and use of renewable energy directly at wastewater treatment plants. This creates an integrated energy system that connects water and energy infrastructure.

Power-to-gas and biomethanation put to the test

At the heart of the project is the conversion of renewable electricity into hydrogen through electrolysis. The hydrogen obtained is then processed into biomethane together with biogenic CO₂ from sewage gas. The project team is also investigating how by-products of electrolysis can be used efficiently. This includes oxygen for wastewater treatment and waste heat for operational processes at the wastewater treatment plant. New control and regulation concepts are intended to enable safe and economical long-term operation.

Energy system model for economic efficiency and electricity market integration

In the project, the RLI experts are developing an open-source energy system model that combines the technical facilities and the requirements of the electricity market. They analyse various electricity price scenarios, operating strategies and marketing channels for hydrogen, biomethane, oxygen and heat in order to assess the economic potential of power-to-gas plants at wastewater treatment plants and identify optimisation opportunities.

Guidelines for the implementation of further projects

In addition to the technical demonstration, the project team is also assessing the environmental impacts and the Germany-wide potential of power-to-gas at wastewater treatment plants. As a result, recommendations for action and a guideline will show how wastewater treatment plants can produce green hydrogen and biomethane economically, safely and sustainably and help operators from the water and energy industries to implement them.

Project period: July 2026 – January 2030

• Demonstration of a power-to-gas plant at two wastewater treatment plants
• Production of green hydrogen by electrolysis
• Conversion of hydrogen and biogenic CO₂ to biomethane
• Integration of power-to-gas into the operation of wastewater treatment plants
• Use of oxygen and waste heat from electrolysis
• Modelling of electricity market and energy system scenarios
• Evaluation of the economic viability of power-to-gas
• Development of new business models for the water and energy industry
• Analysis of the potential of green hydrogen at wastewater treatment plants in Germany
• Preparation of a guideline for practical implementation