The effect of prehydrolysis and improved mixing on high-solids batch simultaneous saccharification and fermentation of spruce to ethanol

Abstract

In the production of ethanol from lignocellulosic material, it is necessary to reach a high ethanol concentration after fermentation. Simply increasing the substrate concentration leads to stirring problems and inhibition of the enzymes and yeast in the process.Batch simultaneous saccharification and fermentation (SSF) of steam-pretreated spruce with 13.7% water-insoluble solids (WIS) (25% total solids (TS)) was run in a stirred-tank reactor as well as in two reactors designed to handle solid or semi-solid material. In all reactors, the overall ethanol yields were only between 5 and 6%. Fermentation of the liquid fraction of the steam-pretreated spruce slurry resulted in an overall ethanol yield of 85%.22h of prehydrolysis at 48°C prior to SSF at 32°C significantly increased the overall ethanol yield to 72% (final ethanol concentration of 47.8g/L), using the whole slurry of steam-pretreated spruce at a dry matter content of 13.7% WIS (25% TS).