Bioenergy production from beach-cast macro algae : The West Coast of Sweden

Abstract: Excessive algae growth/ bloom has become a commonly observed phenomenon in many water bodies globally due to eutrophication. This phenomenon has also been observed in the Baltic Sea which create nuisance in many Baltic coastal communities when the macro algae of different species is washed ashore by wind and wave, which is known as “beach cast algae”. In recent years various Baltic projects have been commenced in order to utilize “beach cast algae” for energy production via anaerobic digestion technology. Harvesting beach cast macro algae for energy production not only give a renewable energy but also improve tourism and recreation, as well as largely contribute towards the marine ecosystem by reducing nutrient load. However, high concentration of heavy metal especially of cadmium in macro algae has limited the potential of anaerobic digestion since cadmium would limit the bio-fertilizer potential of the fermentation residue/digestate. Different heavy metal removal technique has been suggested so far but their potential on large scale application as well as the economic and environmental aspects of the removal techniques are unknown. The present thesis focuses on the west coast of Sweden and evaluate the possibility of combustion of beach cast macro algae in an already existing waste incineration plant. Furthermore, three different scenarios for energy extraction from beach cast macro algae are compared from an energy balance perspective. The study was based on a case study, literature review and energy balance analysis. The result showed combustion of both raw and digested macro algae in an already existing waste incineration plant would give a solution for coastal algae problem regardless of high cadmium content, moisture and ash content of macro algae. Energy extraction via combustion of raw as well as digested macro algae gave a positive energy balance. Anaerobic digestion of macro algae for instance with sewage sludge followed by combustion of the fermentation residue would give more benefit from energy point of view and could be used for cases of beach cast macro algae with high concentration of cadmium.