Bioethanol production from oxalic acid-pretreated biomass and hemicellulose-rich hydrolysates via a combined detoxification process

• The combined detoxification processes removed fermentation inhibitors more efficiently.
• Ferulic acid was the major component in the detoxified hydrolysate.
• Ferulic acid concentration was high in the XAD-ED treated hydrolysate.
• ED-XAD process was most effective for ethanol production in the hydrolysate.
• The theoretical ethanol yields of ED-XAD treated hydrolysate (yellow poplar) was 91.22%.

A combined detoxification process was investigated for ethanol fermentation with hemicellulose rich hydrolysates obtained from mixed hardwood and yellow poplar. Acetic acid was the most abundant compound in the hydrolysates, which also contained inhibitors such as 5-hydroxymethylfurfural (HMF), furfural, and total phenolic compounds (TPC). Electrodialysis (ED) efficiently removed 100% of the acetic acid, whereas most of the HMF, furfural, and TPC remained in the hydrolysates. However, XAD-4 resin removed non-ionizable compounds such as HMF, furfural and TPC. Compared with the single detoxification processes (ED or XAD), the combined detoxification processes (ED-XAD or XAD-ED) removed fermentation inhibitors more efficiently. Compared with XAD-ED, ED-XAD produced higher ethanol yields of 0.48 g/g and 0.49 g/g in mixed hardwood and yellow poplar hydrolysates, respectively. Ferulic acid concentration was high in the XAD-ED treated hydrolysate compare to that of ED-XAD treated hydrolysate. For this reason, ethanol fermentability was higher with ED-XAD-treated hydrolysates compared with XAD-ED-treated hydrolysates. Simultaneous saccharification and fermentation was performed with pretreated biomass. Ethanol production was 23.20 g/L with yellow poplar and 19.14 g/L with mixed hardwood after 120 h of fermentation.