How algae and seaweed are dealt with today: A bad smell and eutrophication!

Eutrophication results in the production of large amounts of filamentous algae and seaweed along the Swedish coasts. In total, this involves up to 80,000 tonnes (wet weight) along the coast of Skåne alone. The algae and seaweed are torn off the seabed by the waves and washed up on the beaches or clumped in the marinas. There, a process of decay begins, which results in a very unpleasant odour. To make the beaches more appealing to bathers, they are cleared away during the summer months and the collected masses of algae and seaweed are piled up in the sand dunes or at a nearby location. After the bathing season has drawn to a close, the collected material, and thereby the nutrients that cause the eutrophication, is returned to the water.

Why make biochar out of algae and seaweed?

Algae and seaweed contain relatively large amounts of phosphorus. By converting the algae and seaweed to biochar, the phosphorus that has previously leaked into the sea from the agricultural land can be returned. The cycle is closed and the need to add newly extracted phosphorus, of which there is currently a limited supply, is reduced.


Algae and seaweed are usually collected from the beaches with the help of a wheel loader, which results in a significant Furthermore, algae and seaweed contain large amounts of water. Both the sand and the water cause difficulties when the material is to undergo pyrolysis and be converted to biochar. Within the project Rest till Bäst, we will collect algae and seaweed using specially adapted machines in the shallow water closest to the water’s edge. In this way, we hope to reduce the amount of sand in the material. We will also carry out experiments where we dry algae and seaweed directly on the beach. In addition to the pyrolysis process working better when the material is more dry (preferably 85% dry matter), drying on site also means that transport to the pyrolysis plant will have a significantly lower climatic impact, as fewer runs are required when the material contains less water.



Markus Paulsson
+46 (0) 46-359 53 36
City of Lund, City Office
221 00 Lund, Sweden


Rest till Bäst is a Vinnova-funded project whose purpose is to develop solutions for managing society’s organic residues and create a much needed beneficial product, while at the same time minimising environmental and climate impact.