Optimization of microwave-assisted FeCl3 pretreatment conditions of rice straw and utilization of Trichoderma viride and Bacillus pumilus for production of reducing sugars

In this study, Box-Behnken design (BBD) and response surface methodology (RSM) were used to optimize microwave-assisted FeCl3 pretreatment conditions of rice straw with respect to FeCl3 concentration, microwave intensity, irradiation time and substrate concentration. When rice straw was pretreated at the optimal conditions of FeCl3 concentration, 0.14 mol/L; microwave intensity, 160 °C; irradiation time, 19 min; substrate concentration, 109 g/L; and inoculated with Trichoderma viride and Bacillus pumilus, the production of reducing sugars was 6.62 g/L. This yield was 2.9 times higher than that obtained with untreated rice straw. The microorganisms degraded 37.8% of pretreated rice straw after 72 h. The structural characteristic analyses suggest that microwave-assisted FeCl3 pretreatment damaged the silicified waxy surface of rice straw, disrupted almost all the ether linkages between lignin and carbohydrates, and removed lignin.

► Rice straw is pretreated by microwave and FeCl3.
► We optimize the microwave-assisted FeCl3 pretreatment conditions of rice straw by RSM.
► Rice straw is degraded with Trichoderma viride CCTCC AF93252 and Bacillus pumilus CCTCC AB93225.
► The degradation with T. viride and B. pumilus can avoid enzyme recycling and eliminate the need to utilize costly enzyme preparations.
► The maximum production of reducing sugars is obtained after the optimization of microwave-assisted FeCl3 pretreatment conditions.