Handling, storage and preservation of cultivated seaweed biomass for fuel production

Macroalgae, or seaweed, have a high sugar content and is a biomass resource suitable for conversion to biofuels. The carbohydrate content of brown algae has large seasonal variations, with a maximum in the period July-October. Storage of the biomass will therefore be necessary to allow year-round manufacturing. This imposes large challenges for the logistics. A high water content compared to terrestrial biomass (straw, wood) makes seaweed more vulnerable to microbial degradation, and preservation of the stored biomass will be required. The aim of the project has been to investigate if the harvesting season could be extended, combined with short- or long-term storage in the sea, and to develop a preservation process for the harvested biomass. A series of field experiments have shown that the optimal harvest window for cultivated seaweed is May-June, which is narrower and earlier than previously expected. This poses additional logistical challenges and results in a lower sugar content than expected from literature data on wild seaweed. The maximum time window between harvesting and chemical preservation has also been determined. A preservation process based on pH-reduction using cheap acids has been developed, ensuring complete preservation of the sugars after 6 months' storage. Based on analyses of soluble compounds and fermentations of the preserved biomass with yeasts, an optimum pH-range has been determined, where maintaining a high solubility of the polysaccharides is balanced with efficient prevention of microbial growth. In summary, the project has provided valuable information about the logistical and economical challenges in industrial scale seaweed biomass production. The successful development of a low cost preservation method is a significant step towards the design of a complete seaweed biomass value chain.

Macroalgae, or seaweed, have a high sugar content, suitable for conversion to biofuels. Norway has a long coastline with favourable climatic conditions for cultivation of sugar-rich brown algae. SES has since 2009 been engaged in development of new techno logy for cultivation of seaweed with test cultivation at various locations in Norway and Portugal. SES entered into a collaboration agreement with Statoil in 2012. Ethanol will probably be the first realizable product, but other fuels, such as butanol and more advanced biofuels may be future products from seaweed. Independent of the fuel product, a high carbohydrate content of the biomass is critical for the fuel yield. The carbohydrate content of brown algae has large seasonal variations, with a maximum in the period July-October. Storage of the biomass will therefore be necessary to allow year-round manufacturing. This imposes large challenges for the logistics. A high water content compared to terrestrial biomass (straw, wood) makes seaweed more vulner able to microbial degradation, and preservation of the stored biomass will be required. To allow year-round fuel production, two strategies exist; 1) extended harvesting season, combined with short- or long-term storage in the sea, and/or 2) preservation of the harvested biomass. Neither of these strategies have previously been explored for the large biomass volumes needed for fuel production. The project will design strategies for handling and storage of harvested biomass. Research tasks include evaluat ion of the stability of harvested biomass in the sea to determine the acceptable time window until preservation is needed, and development of a preservation method that also will be a part of the pre-treatment process.