Eutrophication has both ecological and social consequences and is one of the major environmental problems in the Baltic Sea at the same time there is a need for a transition from a fossil-based to a sustainable bio-based society. Anaerobic digestion offers many opportunities of relevance for the Baltic Sea Region since it transfers low quality resources/wastes into a renewable high quality fuel that can be used for local electricity and heat supply, as transport fuel or for injection into the natural gas grid. In addition, the digestate can replace the fossil based artificial fertilizers, and hence close the nutrients loop which is fundamental for the circular bioeconomy. By using cast seaweed as substrate and utilize the digestate as a fertilizer, nutrients are physically removed from the Baltic Sea and hence provide a powerful tool to mitigate eutrophication. In addition the inconveniences with rotting seaweed on the beaches are removed for the benefit of recreation, tourism and increased value of residential properties along the coast. Practically, experiences and results from industrial scale anaerobic co-digestion of cast seaweed in Denmark will be further improved and adapted to local conditions in the participating countries into the South Baltic (SB) Sea area, supported by technology implementation by informing responsible key institutions. Targeted technology transfer and cross-border cooperation in combination with feasibility studies and pilot testing will contribute to market uptake and the first step of a wider implementation of this new and innovative technology in the South Baltic Sea area. The overall aim is to create a guideline for using seaweed as co-digestive e.g. for municipalities and/or biogas operators in coastal areas of the SB Sea region and to create incentives in order to financially support innovative technology, i.e. collecting and cleaning methods, and the application in a biogas plant, including also technical and legal guidelines.