Hydrolysate-Recycled Liquid Hot Water Pretreatment of Reed Straw and Corn Stover for Bioethanol Production with Fed-Batch, Semi-Simultaneous Saccharification and Fermentation

Prehydrolysates and water-insoluble solids (WISs) were produced from reed straw and corn stover pretreated with hydrolysate-recycled liquid hot water (LHW) at different cycle times. The chemical components of the prehydrolysates and WISs were then investigated to assess the possible effects of hydrolysate recycling on bioethanol production. The WISs were subjected to fed-batch, semi-simultaneous saccharification and fermentation (S-SSF) to investigate the changes in bioethanol concentration and evaluate the efficiency of the pretreatment. The pretreatment conditions consisted of a temperature of 195 degrees C, time of 20 min, and liquid ratio of 1:20. The prehydrolysates were recycled using a circulation volume of 50% and were applied to 10 cycles. The results showed that recycling did not significantly decrease the pH of the hydrolysates. The content of glucose and xylan in the hydrolysates decreased and then increased with increasing cycle times. In the WISs, the contents of benzene alcohol extractives and ash increased remarkably. The content of acid-insoluble lignin and glucan increased slightly. The amounts of xylan and acid-soluble lignin in the WISs were low, and the changes in these contents were not significant. Thus, hydrolysate-recycled LHW pretreatment was beneficial for bioethanol production from reed straw, but not from corn stover.