Microbial hydrolysis and fermentation of rice straw for ethanol production

In this work, Trichoderma reesei Aq-5b and Trichoderma viride NSW-XM, capable of excreting lignin-degrading enzymes and cellulase were used to create a mixed culture system to hydrolyze rice straw in situ. The results showed that Aq-5b and NSW-XM were able to co-grow and produce complementary lignin degrading enzymes, namely laccase and lignin peroxidase. The two microorganisms were able to produce 22.74 g/L of reducing sugar in the optimal condition. For fermentation of the hydrolysates produced, Saccharomyces cerevisiae and Candida tropicalis NSW-NW were co-immobilized in polymer beads composed of sodium alginate, polyvinyl alcohol, and silicon dioxide (SA-PVA-SiO₂). The beads remained intact after 4 cycles of use and provided satisfactory protection for the yeasts and a suitable microenvironment for ethanol fermentation, greatly improved the efficiency of ethanol production, shortened the fermentation cycle and achieved yeasts recycling for continuous or batch-fed fermentation. The productivity of ethanol reached up to 2.17 g/(L h).