High titer ethanol production from an atmospheric glycerol autocatalytic organosolv pretreated wheat straw

Abstract:

The expensive production of bioethanol is because it has not yet reached the ‘THREE-HIGH’ (High-titer, high-conversion and high-productivity) technical levels of starchy ethanol production. To cope with it, it is necessary to implement a high-gravity mash bioethanol production (HMBP), in which sugar hydrolysates are thick and fermentation-inhibitive compounds are negligible. In this work, HMBP from an atmospheric glycerol autocatalytic organosolv pretreated wheat straw was carried out with different fermentation strategies. Under an optimized condition (15% substrate concentration, 10 g/L (NH4)2SO4, 30 FPU/g dry matter, 10% (V/V) inoculum ratio), HMBP was at 31.2 g/L with a shaking simultaneous saccharification and fermentation (SSF) at 37 °C for 72 h, and achieved with a conversion of 73% and a productivity of 0.43 g/(L·h). Further by a semi-SFF with pre-hydrolysis time of 24 h, HMBP reached 33.7 g/L, the conversion and productivity of which was 79% and 0.47 g/(L·h), respectively. During the SSF and semi-SSF, more than 90% of the cellulose in both substrates were hydrolyzed into fermentable sugars. Finally, a fed-batch semi-SFF was developed with an initial substrate concentration of 15%, in which dried substrate (= the weight of the initial substrate) was divided into three portions and added into the conical flask once each 8 h during the first 24 h. HMBP achieved at 51.2 g/L for 72 h with a high productivity of 0.71 g/(L·h) while a low cellulose conversion of 62%. Interestingly, the fermentation inhibitive compound was mainly acetic acid, less than 3.0 g/L, and there were no other inhibitors detected, commonly furfural and hydroxymethyl furfural existing in the slurry. The data indicate that the lignocellulosic substrate subjected to the atmospheric glycerol autocatalytic organosolv pretreatment is very applicable for HMBP. The fed-batch semi-SFF is effective and desirable to realize an HMBP.