Pretreatment of switchgrass with electrolyzed water and a two-stage method for bioethanol production

In this study, switchgrass, which is a promising energy crop, was treated with two new pretreatment methods for the production of bioethanol. Acidic electrolyzed water (AEW) and alkaline electrolyzed water (ALEW) were first used as pretreatment catalysts at three temperatures (170, 185, and 200°C) and 3 treatment times (5, 15, and 25 min). In the two-stage pretreatment, 1.0, 2.0 and 3.0% H2O2 solutions were used to partially remove hemicellulose and lignin during the 1st stage at 50°C for 16, 24, or 32 h at a solid concentration of 5%. The supernatant of the 1st stage was used for hemicellulose precipitation. The remaining solids were subjected to a 2nd stage treatment with hot water at 121°C for 30 min in an autoclave at a solid concentration of 12.5%. In the electrolyzed water pretreatment, the highest glucose yield was achieved by pretreatment with ALEW at 200°C and 25 min, which resulted in the release of 23.8 g glucose from 100 g dry switchgrass. The hydrolyzate obtained from switchgrass pretreated with 3% H2O2 for 16 h followed by enzymatic hydrolysis was fermented using S. cerevisiae at 30°C for 96 h without any concentration or detoxification steps. The final ethanol concentration was 11.8 g/L and the productive yield was 74% of the theoretical yield. A mass balance for the two-stage process showed that 12 g of ethanol was produced from 100 g dry switchgrass.