Cellulase Production By Submerged Fermentation And Bioconversion Of Poplar Wood To Ethanol

With the rising tightness of the world's energy supply, growing attention has been devoted to fuel ethanol, but the real cause lied deeper is the inevitable depletion of fossil fuels. However, nearly all bioethanol fuel is produced by fermentation of sugar from food crops. On the other hand, the utilization of cellulosic materials with relatively low cost and plentiful supply is very limited. The central technological impediment to bioconversion of lignocellulosic biomass to ethanol is the general absence of low-cost and efficient technology for delignification to liberate cellulose and hemicellulose from their complex with lignin, depolymerization of cellulose and hemicellulose to monose, and fermentation of mixed hexose and pentose to ethanol.First, the effects of inoculums and proportion of microcrystalline cellulose and bran on the cellulase yield by Trichoderma reesei Rut C-30 were examined in this study. The results showed that the differences of effects among nine inoculums were significant and proper content of bran improve the cellulase production. With Design-Expert, the design of the quadratic rotation-regression-orthogonal combination was done, and a point corresponding to 1.223% cellulose and 2.350% bran was suggested as an optimum proportion. Experiment running under the optimum condition in 7.5 L fermentor, filter paper activity and yield coefficient reached 6.383 IU/ml,17.403% higher than that before optimization, and 521.913 FPIU/g cellulose,4.004% lower than that before optimization. And then experiments replacing cellulose with dilute-acid pretreated poplar or steam exploded poplar as substrate were carried out and filter paper activity were 1.953 IU/ml and 1.745 IU/ml.Second, dilute acid pretreatment of poplar wood and its simultaneous saccharification and fermentation (SSF) for ethanol were studied. Pretreatment was performed in a simple reactor. The maximum hemicellulose recovery from poplar powder (15.0%, w/v) by sulphuric acid pretreatment (0.4%,190℃,75 min) was 65.9%. The concentration of ethanol from solid residue by Escherichia coli KO11 was 9.7 g/l, corresponding to 63.3% of the maximum theoretical yield based on glucan of solid residue. The concentration of ethanol from liquid residue after overliming was 12.4 g/1, corresponds to 56.9% of the maximum theoretical yield based on reducing sugar in liquid residue.Third, steam explosion of poplar wood and its simultaneous saccharification and co-fermentation (SSCF) for ethanol were studied. The concentration of ethanol from steam exploded poplar wood by E.coli KO11 was 3.6 g/l, corresponding to 51.4% of the maximum theoretical yield based on glucan of solid residue.Finally, scanning electron microscopy (SEM), FT-IR spectroscopy and X-ray diffraction results indicated that changes of cellulosic materials in physical/chemical happened after dilute acid pretreatment and steam explosion. It is postulated that these physical/chemical changes enhance the enzymatic digestibility in the pretreated poplar wood.