Ethanol production from Saccharina japonica using an optimized extremely low acid pretreatment followed by simultaneous saccharification and fermentation

► SSF conducted with extremely low acid pretreated Saccharina japonica, for bioethanol production. ► ELA pretreatment of algal biomass does not require processes such as neutralization. ► Three suspensions; buffer, deionized water and treated liquid hydrolysate were used for SSF. ► Deionized water as a fermentation broth may be possible for high bioenergy yield. ► Liquid hydrolysate of S. japonica can be used for biofuel fermentation using other microorganisms. An extremely low acid (ELA) pretreatment using 0.06% (w/w) sulfuric acid at 170°C for 15min was employed to extract non-glucan components from Saccharina japonica, a brown macroalgae. Subsequent simultaneous saccharification and fermentation (SSF) was conducted using Saccharomyces cerevisiae DK 410362 and cellulase (15 FPU/g-glucan) and ß-glucosidase (70 pNPGU/g-glucan). Deionized water was used for making fermentation suspension. After the ELA pretreatment, a glucan content of 29.10% and an enzymatic digestibility of 83.96% was obtained for pretreated S. japonica. These values are 4.2- and 2.4-fold higher, respectively, than those of obtained with untreated S. japonica. In SSF, a bioethanol concentration of 6.65g/L was obtained, corresponding to a glucose equivalent concentration of 13.01g/L, which indicated an SSF yield of 67.41% based on the total available glucan of the pretreated S. japonica. The remaining separated liquid hydrolysate, which contains mannitol and alginate-derived oligosaccharides can be applied to other fermentations.