The prevalent species are the green seaweed common eelgrass – Zostera marina, the brown seaweed bladder wrack – Fucus versiculosus and the brown algae – Pylaiella littoralis. They are marine species, which grow on available substrates and provide many services for the ecosystem. Macroalgal roots serve as natural erosion protection for the sediment and have high importance as food and breeding habitat. Mats of macrophyta are able to float over great distances and accumulate at the water-line on beaches.

Algae can absorb, therewith purify and remove nutrients from the surrounding water volume. They can take up excess nutrients and unbound elements and, in this regard, multiply their biomass quickly. Worldwide the excessive growth of macroalgae is occurring as a sign of the eutrophication phenomenon. In the process high amounts of nitrogen (N) and phosphorous (P) are consumed from environment in which the algae are located. This characteristic is excellently applicable for the selected uptake of element surplus from the environment.

Based on currently applicable techniques seaweed (macroalgae) is collected along the coast line on the beach (onshore) and in the shallow water nearby the beach (offshore). First, the algal biomass is pre-treated via sieving and washing. The pre-treated material can potentially be fermented (co-digested) with other residual material in an oxygen free (anaerobic) decomposition (digestion) procedure at a biogas plant or wastewater treatment plant. Biogas can be used to fuel a combined heat and power unit or upgraded to biomethane. Depending on the season and region, contaminant thresholds in algal biomass may be too high. In such cases other applications can be found for the organic residues.

The image shows the process of collecting, cleaning and utilising seaweed for energy.