Separate hydrolysis and co-fermentation for improved xylose utilization in integrated ethanol production from wheat meal and wheat straw

Separate hydrolysis and co-fermentation of steam-pretreated wheat straw (SPWS) combined with wheat-starch hydrolysate feed was performed in two separate processes. The average yield of ethanol and the xylose consumption reached 86% and 69%, respectively, when the hydrolysate of the enzymatically hydrolyzed (18.5% WIS) unwashed SPWS solid fraction and wheat-starch hydrolysate were fed to the fermentor after 1 h of fermentation of the SPWS liquid fraction. In the other configuration, fermentation of the SPWS hydrolysate (7.0% WIS), resulted in an average ethanol yield of 93% from fermentation based on glucose and xylose and complete xylose consumption when wheat-starch hydrolysate was included in the feed. Increased initial cell density in the fermentation (from 5 to 20 g/L) did not increase the ethanol yield, but improved and accelerated xylose consumption in both cases.Higher ethanol yield has been achieved in co-fermentation of xylose and glucose in SPWS hydrolysate when wheat-starch hydrolysate was used as feed, then in co-fermentation of the liquid fraction of SPWS fed with the mixed hydrolysates. Integration of first-generation and second-generation processes also increases the ethanol concentration, resulting in a reduction in the cost of the distillation step, thus improving the process economics.The use of bioethanol is beneficial for several reasons. One is that it can be easily integrated into the current fuel distribution system, and another is that it will reduce the production of greenhouse gases as the raw material used is biomass. Bioethanol can be produced from lignocellulosic biomass in three main steps: pretreatment, enzymatic hydrolysis, and fermentation. Enzymatic hydrolysis and fermentation can be carried out either separately, using separate hydrolysis and fermentation (SHF), or simultaneously, using simultaneous saccharification and fermentation (SSF).Over the past decade SSF has become the preferred process, since end-product inhibition of the