Saltwater based fractionation and valorisation of macroalgae

BACKGROUND Macroalgae are gaining increasing interest as an important biomass feedstock. Yet when valorising marine biomass, the presence of salt can pose a substantial obstacle to the effectiveness of downstream biological and chemical processes, as well as the engineering infrastructure required. Accordingly, dewatering, washing and drying are often considered the first and crucial primary steps in processing marine biomass such macroalgae. The high costs of these processes can make further marine biorefinery commercialisation prohibitive. This investigation assesses simple pre-treatments for macroalgal biomass in saltwater, thereby reducing the freshwater footprint, and removing the need for an energy-intensive washing and drying stage. RESULTS Using acid and basic catalysts, the carbohydrate and soluble protein components were fractionated into a soluble aqueous phase, for further fermentation and a solid phase suitable for hydrothermal liquefaction. The presence of saltwater was found to aid the fractionation process, solubilising more of the biomass. The use of H2SO4 produced more monosaccharides, whereas NaOH solubilised higher levels of biomass at lower temperatures. The aqueous phase was demonstrated to be suitable for biological processing with the salt tolerant yeast Metschnikowia pulcherrima, and the residual solids suitable for processing via hydrothermal liquefaction. CONCLUSION By contrast with existing pre-treatment strategies, we demonstrate that an entirely salt-based biochemical conversion route is a potentially viable option. For the first time this work demonstrates that, rather than a hindrance, the presence of saltwater can be advantageous, and could provide an alternative, more cost-effective pathway to achieving a successful macroalgal-based biorefinery.