Efficiency of cellulosic ethanol production by Saccharomyces cerevisiae and Mucor indicus from biomass after microwave-assisted pretreatment with aqueous solutions of deep eutectic solvents

Current trends promote a reduction of the quantity of chemicals used and resorting to energy-effective methods of heating biomass. This study aims to assess the usefulness of microwave radiation and selected aqueous solutions of deep eutectic solvents in preparing oat hull or brewer's spent grain biomass for the production of cellulosic ethanol. Fermentation was carried out using the Saccharomyces cerevisiae or Mucor indicus. Oat hull pretreatment using an aqueous solution of choline chloride and ethylene glycol led to the generation of biomass highly susceptible to enzymatic degradation. The above resulted in hydrolysates containing 116.8 g/L of glucose, which constituted complementary fermentation media for yeast (S. cerevisiae) enabling comprehensive attenuation within 48 h and the generation of ethanol concentration at 54.5 g/L. The use of S. cerevisiae resulted in a faster conversion of glucose to ethanol in comparison with M. indicus, regardless of the plant biomass type. Additionally, the acquired lignocellulosic hydrolysates, after supplementation with amino nitrogen compounds, constituted a medium facilitating an effective production of M. indicus biomass under oxygen conditions. Tests clearly indicate the possibility of using the developed pretreatment method in the cellulosic ethanol production.