Microwave assisted pretreatment of eucalyptus sawdust enhances enzymatic saccharification and maximizes fermentable sugar yield

There is an urgent need of sustainable and efficient methods for the production of biofuels and chemicals from lignocellulosic feedstock. The purpose of this study was to develop a mild, cost-effective and environmentally benign pretreatment for woody lignocellulose to maximize sugar yield via enzymatic saccharification. Microwave irradiation (MW) of Eucalyptus regnans sawdust in water was investigated and compared directly against conventional liquid hot water (LHW) pretreatment. Following 30 min microwave irradiation at 180 °C, the sugar yield was 3.5 times higher using MW than LHW pretreatment under the same conditions. Complete release of C5 and C6 sugars was achieved after the two-step method of MW pretreatment followed by enzymatic hydrolysis, compared with only 4% without pretreatment and 31% after LHW. Removal of ‘lignin droplets’ formed on the surface of the pretreated fibers via flowing hot water showed only minor improvement in the yield of enzymatic saccharification. Our results support the hypothesis that lignin prevents access of enzymes rather than inhibits their activity. MW accelerated depolymerization of hemicellulose, opening the structure more than LHW pretreatment.