Synthesis of Bioethanol from Oat Husk via Enzyme-Substrate Feeding

Abstract

A promising way of utilizing oat husks is its bioconversion into technical bioethanol. Ways of increasing the concentration of bioethanol in the mash must be found to increase the economic efficiency of the process. A combination of enzymatic hydrolysis and alcoholic fermentation (combined biocatalytic stages, or CBS) can be used to obtain bioethanol. In addition, delayed introduction of the inoculum can be used when combining stages. In this work, a comparative study is performed of the CBS processes with an initial substrate concentration of 60 g/L (one-time substrate loading) and an increased substrate concentration of 120 g/L after enzyme–substrate feeding (loading the substrate at a concentration of 60 g/L at the beginning of the process and feeding 30 g/L of the substrate after 4 and 8 hours. The substrate is oat husks treated with 4 wt % nitric acid in a pilot plant; a multi-enzyme composition of industrial preparations Cellolux-A and Ultraflo Core is used for enzymatic hydrolysis. Alcohol is fermented using the yeast Saccharomyces сerevisiae Y-1693 (VKPM). The equipment is a fermenter with a capacity of 11 L. Feeding with a doubled concentration of the substrate raises the concentration of bioethanol by 1.7 times (from 2.4 to 4.0 vol %) but lowers its yield by 11.4%. Make-up regimes are being developed that ensure higher concentrations of bioethanol in the mash without reducing its yield.