Enhancement of sugar recovery and ethanol production from wheat straw through alkaline pre-extraction followed by steam pretreatment

• Published in: Bioresource technology 2018-10, Vol.266, p.194-202
• Main Authors: Yuan, Zhaoyang, Li, Guodong, Hegg, Eric L.
• Format: Article
• Language: English
• Subjects: Alkaline pre-extraction; Enzymatic hydrolysis; Ethanol; High solid loading; Steam pretreatment; Wheat straw
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2018.06.065

•Alkaline pre-extraction improved wheat straw fractionation during steam treatment.•Steam pretreatment of NaOH-extracted wheat straw produced low amount of inhibitors.•Sequential NaOH-steam pretreatment enabled efficient hydrolysis of wheat straw.•Two-stage treated wheat straw was readily hydrolyzed at up to 25% solid loading.•An ethanol yield of 237 kg/ton of wheat straw at a titer of 54.5 g/L was achieved. To improve sugar recovery and ethanol production from wheat straw, a sequential two-stage pretreatment process combining alkaline pre-extraction and acid catalyzed steam treatment was investigated. The results showed that alkaline pre-extraction using 8% (w/w) sodium hydroxide at 80 °C for 90 min followed by steam pretreatment with 3% (w/w) sulfur dioxide at 151 °C for 16 min was sufficient to prepare a substrate that could be efficiently hydrolyzed at high solid loadings. Moreover, alkaline pre-extraction reduced the process severity of steam pretreatment and decreased the generation of inhibitory compounds. During enzymatic hydrolysis, increasing solid loading decreased the yield of monomeric sugars. Enzymatic hydrolysis at 25% (w/v) solid loading, the yields of approximately 80% of glucose and 65% of xylose could be reached with an enzyme dosage of 25 mg protein/g glucan. Following fermentation of hydrolysate with sugar concentration of approximately 120 g/L, an ethanol concentration of 54.5 g/L was achieved.