The production of bioethanol from oat hulls by enzyme-substrate replenishment

Abstract

A promising way for oat hulls utilization is their bioconversion to industrial bioethanol. To improve economic efficiency of the process, it is necessary to increase the concentration of bioethanol in the wash. Here, bioethanol was produced using a combination of enzymatic hydrolysis and alcoholic fermentation, i.e. a combination of biocatalytic steps; in addition, a delayed introduction of inoculum was used. The aim of the work was a comparative study of the indicated processes at the initial concentration of substrate 60 g/l (single loading of the substrate) and upon its increase to 120 g/l by enzyme-substrate replenishment (loading of the substrate in the concentration 60 g/l at the beginning of the process, and replenishment after 4 and 8 h with 30 g/l of the substrate). The substrate was represented by oat hulls treated with 4 wt.% nitric acid on a pilot production plant; enzymatic hydrolysis was carried out using a multienzyme composition of commercial enzyme preparations Cellolux-A and Ultraflo Core; alcoholic fermentation was performed with the yeast Saccharomyces сerevisiae Y-1693 (Russian Collection of Industrial Microorganisms); equipment – a fermenter of volume 11 l. A twofold increase in the substrate concentration via the replenishment led to an increase in bioethanol concentration by a factor of 1.7 (from 2.4 to 4.0 vol.%) but decreased its yield by 11.4 %. The replenishment modes providing an increased concentration of bioethanol in the wash without a decrease in its yield are under development.