Advances in the pretreatment of brown macroalgae for biogas production

Abstract

Brown macroalgae are an attractive, untapped resource and a favourable alternative for conventional fossil fuels, given their low lignin and high polysaccharide content. However, the restricted bioavailability of structurally complex carbohydrates for digestion, results in a low biomethane potential. This paper reviews the various pretreatment technologies explored to optimise saccharification prior to fermentation, categorised as: physical, biological, chemical, thermal and a combination of methods. A techno-economic assessment was conducted to evaluate the commercial viability of each process. Hydrothermal pretreatment proves the most promising technique for brown algae application, since it improves methane productivity, carries a net positive energy balance and generates a bio-fertilizer, while mitigating greenhouse gas emissions. Pilot scale research is necessary to evaluate the feasibility of full-scale implementation for brown algae bioconversion. A case study of the Cambi™ process concludes the paper as it exemplifies the successful utilisation of hydrothermal pretreatment for sewage sludge biogas production.