Enhancement of high-solids enzymatic hydrolysis and fermentation of furfural residues by addition of Gleditsia saponin

•High-solids enzymatic hydrolysis with the addition of GS was investigated.•A hydrolysate with 115.4 g/L glucose was obtained.•Ethanol (69.1 g/L) was produced with a total cellulose conversion of 82.2%.•The accumulated sugar in high-solids enzymatic hydrolysis led to a low glucose yield.•GS improved glucose yield greatly, especially for FRs with high lignin content.

Gleditsia saponin (GS) assisted high-solids enzymatic hydrolysis and fermentation for alkaline peroxide (AP)-pretreated furfural residues (FRs) was investigated. The addition of GS increased the glucose yield of untreated FRs to 74.8% in high-solids-loading enzymatic hydrolysis. AP pretreatment before enzymatic hydrolysis resulted in a high sugar concentration (115.4 g/L) and a glucose yield of 57.5% by the end of hydrolysis at 20% solids loading. It was suggested that GS could improve significantly the glucose yields of FRs with high lignin content. After simultaneous saccharification and fermentation (SSF), the total cellulose conversion of FRs with 14.3% lignin content reached 82.2% and the highest ethanol concentration (69.1 g/L) was achieved, which was 121% higher than that of untreated FRs (30.1 g/L). The results indicated that the main reason behind the decreased glucose yield at high-solids loadings was product inhibition. Moreover, the lignin content plays an important role in the enhancement of GS-assisted high-solids enzymatic hydrolysis of AP-treated FRs.