Bioprocessing of rice husk into monosaccharides and the fermentative production of bioethanol and lactate

Rice husk, a residue from agro-industrial processing, is one of the most abundant lignocellulosic feedstocks in South Brazil. In the present study, the uncatalysed steam-exploded rice husk slurry was separated into liquid and solid fractions. The liquor was efficiently hydrolysed using an enzymatic complex produced from the Penicillium echinulatum S1M29 strain, followed by lactic acid production using Lactobacillus buchneri NRRL B-30929, which can consume a blend of xylose and glucose. The laboratory-produced enzyme cocktail proved to be a successful strategy for hydrolysis of the liquor, without the release of by-products that occurs during the usual acid hydrolysis technique. The water-insoluble solids were subjected to simultaneous saccharification and fermentation processes using high solid loading combined with distinct doses of commercial enzymes, producing ethanol via Saccharomyces cerevisiae CAT-1. In total, 12.69 g L−1 lactic acid and 19.17 g L−1 ethanol were produced, demonstrating that this abundant low-value renewable feedstock can be explored using a cleaner, greener, and environmentally friendlier production process.