Improvement of the hydrolysis and fermentation of rice straw by Saccharomyces cerevisiae by ammonia-based pretreatments

Abstract

This work aimed at improving the hydrolysis and fermentation processes of rice straw through different ammonia-based pretreatments to aid in bioethanol production. For this purpose, pretreatment was performed at 70 °C for 12 h, followed by enzymatic hydrolysis at 50 °C for 24 h and 72 h using 15 FPU cellulase and 30 CBU cellobiase. The best hydrolysis yield, based on the production yield and rate, for the 24-h digestion period was samples that had been soaked in methanolic aqueous ammonia (SMAA), with 72% of the theoretical maximum. However, for the 72-h digestion period, soaking in ethanolic aqueous ammonia (SEAA) was the best method, with 88% yield. In the case of ethanol production after 24 h, the SMAA pretreatment and SSF resulted in the highest yield at 72%. However, after 72 h of simultaneous saccharification and fermentation (SSF), SMAA-pretreated rice straw showed a yield of 85%, while the SEAA-pretreated sample resulted in a noteworthy yield of 89% of the theoretical maximum. However, with regard to the production yield and rate and pretreatment cost, the best method for ethanol production was judged to be the SMAA with 5% methanol, particularly after 24 h of SSF.