Ethanol production from steam-pretreated sweet sorghum bagasse with high substrate consistency enzymatic hydrolysis

In this work, separate hydrolysis and fermentation (SHF) and simultaneous saccharification fermentation (SSF) with high substrate consistency (the mass fraction: 12%) were performed with the steam-pretreated sweet sorghum bagasse (SSB). Fermentation ability of four yeast strains and influences of residual solids after hydrolysis on fermentation were investigated in SHF. Meanwhile, influences of inorganic salts on fermentation were assessed to determine their suitable supplementations for ethanol production. Additionally, influences of initial yeast inoculation on SHF and SSF were further investigated. The results showed the adopted yeast strain, Tembec 1, displayed the best fermentation performance on the hydrolysate of pretreated SSB, and the residual solids in hydrolysate had negligible influences on ethanol fermentation. Although the deficiency or overdose of (NH4)2HPO4 or MgSO4·7H2O could reduce ethanol yield in SHF, the suitable supplementation of (NH4)2HPO4 (0.5 g L−1) and MgSO4·7H2O (1.0 g L−1) could increase ethanol yield by 5.2% and 8.3%, respectively. The initial yeast inoculation of 3 g L−1 could satisfy both SSF and SHF, which achieved 63.8% and 57.9% ethanol yield of theoretical one with final ethanol concentration of 23.3 g L−1 and 21.2 g L−1, respectively. In addition, ethanol yield kept almost constant as yeast was inoculated from 3 to 5 g L−1 in SHF, whereas it decreased significantly in SSF.

► Steam-pretreated SSB with high substrate consistency was used for SHF and SSF.
► Residual solids in hydrolysate had negligible influences on ethanol yield in SHF.
► Suitable addition of (NH4)2HPO4 (0.5 g L-1) increased ethanol yield by 5.2% in SHF.
► Suitable addition of MgSO4·7H2O (1.0 g L-1) increased ethanol yield by 8.3% in SHF.
► Initial yeast inoculation of 3 g L-1 could satisfy SHF and SSF.