Detoxification of Hydrolysates of the Red Seaweed Gelidium amansii for Improved Bioethanol Production

In this study, bioethanol was produced from the seaweed Gelidium amansii as biomass through separate hydrolysis and fermentation (SHF) processes. The SHF processes examined in this study include thermal acid hydrolysis pretreatment, enzymatic saccharification, detoxification, and fermentation. Thermal acid hydrolysis pretreatment was conducted using H2SO4, with a slurry content of 8–16% and treatment time of 15–75 min. The optimal conditions for thermal acid hydrolysis pretreatment were 12% (w/v) seaweed slurry content and 180 mM H2SO4 at 121 °C for 45 min, at which 26.1 g/L galactose and 6.8 g/L glucose were produced. A monosaccharide (mainly glucose) was also obtained from the enzymatic saccharification of thermal acid hydrolysate using 16 U/mL Celluclast 1.5 L enzyme at 45 °C for 36 h. Detoxification was performed using the adsorption method with activated carbon, the overliming method with Ca (OH)2, and the ion exchange method with polyethyleneimine. Among those detoxification methods, activated carbon showed the best performance for hydroxymethylfurfural removal. Ethanol fermentation was performed using 12% (w/v) seaweed hydrolysate with Saccharomyces cerevisiae adapted to galactose as well as various detoxification treatments.