Pretreatment of wheat straw using combined wet oxidation and alkaline hydrolysis resulting in convertible cellulose and hemicellulose

Abstract

The wet oxidation process of wheat straw has been studied as a pretreatment method to attain our main goal: To break down cellulose to glucose enzymatic, and secondly, to dissolve hemicellulose (e.g., for fermentation) without producing microbial inhibitors. Wet oxidation combined with base addition readily oxidizes lignin from wheat straw facilitating the polysaccharides for enzymatic hydrolysis. By using a specially constructed autoclave system, the wet oxidation process was optimized with respect to both reaction time and temperature. The best conditions (20 g/L straw, 170°C, 5 to 10 min) gave about 85% w/w yield of converting cellulose to glucose. The process water, containing dissolved hemicellulose and carboxylic acids, has proven to be a direct nutrient source for the fungus Aspergillus niger producing exo-β-xylosidase. Furfural and hydroxymethyl-furfural, known inhibitors of microbial growth when other pretreatment systems have been applied, were not observed following the wet oxidation treatment.