An integrated process to produce bio-ethanol and xylooligosaccharides rich in xylobiose and xylotriose from high ash content waste wheat straw

•An integrated process for bio-ethanol and XOS productions from straw pulping residue.•Prewashing step greatly improved enzymatic glucose yield and XOS content.•Highly similar ethanol yields were obtained from SSF at varied substrate loadings.•Enzymatic post-hydrolysis significantly increased xylobiose and xylotriose.

A bio-refinery process of wheat straw pulping solid residue (waste wheat straw, WWS) was established by combining prewashing and liquid hot water pretreatment (LHWP). The results showed that employing a prewashing step prior to the LHWP remarkably improved enzymatic glucose yields from 39.7% to 76.6%. Moreover, after 96 h simultaneous saccharification and fermentation (SSF), identical ethanol yields of 0.41 g/g-cellulose were obtained despite varied solid loadings (5-30%). Beyond ethanol, enzymatic post-hydrolysis of the prehydrolyzate effectively increased xylobiose and xylotriose yields from 15 mg/g-WWS and 14 mg/g-WWS to 53 mg/g-WWS and 20 mg/g-WWS, respectively. For mass balance, about 10.9 tons raw WWS will be consumed to produce 1 ton ethanol, in addition to producing 614.8 kg xylooligosaccharides (XOS) containing 334.3 kg xylobiose and 124.8 kg xylotriose. The results demonstrated that the integrated process for the WWS bio-refinery is promising, based on value-adding co-production in addition to robust ethanol yields.