A review of the current potential of European brown seaweed for the production of biofuels

In addition to the other uses for macroalgae, since the 1970s, there has been interest in using macroalgae as a source of biofuels, due to the high rates of productivity and intrinsic advantages over other biofuel crops such as not requiring land use or significant freshwater input. A wide range of conversion processes exist but anaerobic digestion was one of the first demonstrated and is still a widely proposed conversion pathway. To be economically viable and scalable within Europe, the industry will need to be based on a small number of fast growing, high-yielding European macroalgae species. There is a wide body of scientific work on the conversion of seaweeds to biofuel via anaerobic digestion. These studies demonstrate that the efficiency of this conversion pathway is highly variable between species, processing techniques, composition and digestor conditions. In this paper, we review this body of work specifically linking it to candidate species for European macroalgae bio-energy cultivation with the aim to promote the future development of the European macroalgal cultivation sector and allow for a better alignment with the requirements for biofuel production from macroalgae. Overall, anaerobic digestion of seaweed offers opportunities for large-scale energy production which avoids some of the issues that have faced previous generations of biofuels, but there are a number of key challenges to overcome to ensure wider adoption and economic viability. (1) Optimising the biomass production to ensure an economic and uniform feedstock with the composition optimised to increase desirable characteristics such as sugar content and the carbon and nitrogen ratio and to reduce inhibitory factors such as halogenated secondary metabolites, sulphur and heavy metals. (2) Improving conversion rates through co-digestion, pre-treatments and tailored microbial communities, using scalable and economically feasible technology. (3) Developing tailored microbial communities capable of utilising the diverse polysaccharides in seaweed feedstock and being tolerant of the saline conditions associated with them. Addressing these issues will deliver significant benefits towards the development of a bio-energy industry based on the anaerobic digestion of cultured seaweeds.