Effects Of Pretreatment On Improving Saccharification Efficiency And Adsorption Of Cellulase Onto Rice Straw

As abundant and cheap raw materials, agricultural residues are of great potential for theproduction of bioethanol in china. Pretreatment is essential for destroying the structure oflignocellulosic biomass and enhancing efficiency of enzymatic hydrolysis. In this study, theeffects of sodium sulfite （Na₂SO₃） and sodium carbonate （Na₂CO₃）, as well as steam explosionwith sodium carbonate pretreatment on the chemical composition and enzymatic hydrolysis ofrice or wheat straw were investigated. For further understanding enzymatic hydrolysis, cellulaseadsorption of rice straw from sodium sulfite and sodium carbonate pretreatment was alsodiscussed.Sodium sulfite pretreatment could significantly improve delignification while most of thesugars were kept in pulp. Raising the temperature or increasing the charge of sodium sulfite canimprove the dissolution of lignin and saccharification efficiency. However, when the dissolutionof lignin attained40%, the improvement of saccharification efficiency was nonsignificant. Afterenzymatic hydrolysis, total sugar conversion rate of74.9%and total sugar yield rate of43.5%can be achieved by using the substrate pretreated under the condition of temperature140°C,sodium sulfite charge16%and cellulase loading20FPU/g cellulose.To sodium carbonate pretreatment, lignin removal and polysaccharides loss in pulp wereenhanced with the increase of temperature and TTA charge, of which xylan acted more sensitivethan glucan. The sugar recovery of enzymatic hydrolysis could be increased with relativelyhigher enzyme loading, it went up fast when the TTA charge was added from0%to8%, andthen tended to become gentle or a little bit down with the upgoing of TTA. The highest sugarrecovery of rice straw pretreated by sodium carbonate was obtained with the pretreatmenttemperature140°C, TTA charge8%and the cellulase loading20FPU/g cellulose, which were71.7%and41.6%for total sugar recovery and total sugar yield, respectively.To steam explosion pretreatment with sodium carbonate of wheat straw, lignin content inpretreated wheat straw reduced with the increasing charge of sodium carbonate, while xylanand araban contents went up in pretreated substrate. However, when the sodium carbonatecharge reached8%, the chemical components in pretreated substrate remained stable with thecontinuous increasing charge. Wheat straw pretreated without sodium carbonate showed thehighest glucan yield in enzymatic hydrolysis with a low enzyme dosage. Except thepretreatment without sodium carbonate, a higher lignin content showed negative effect on the glucan and total sugar yield to enzymatic hydrolysis, while the effect became small when ahigher enzyme dosage was employed.Adsorption of cellulase onto rice straw pretreated by sodium sulfite （SS） and sodiumcarbonate （SC） under controlled temperature and chemical charge was investigated. Langmuiradsorption parameters were then estimated by non-linear regression using Origin8.0. Residuallignin in substrate showed some adverse effect on the enzyme adsorption onto the substrates.Cellulase adsorption was obviously improved with the lignin removal. The effect of lignin oncellulase adsorption became very little when lignin removal was over30%for SC pretreatedand50%for SS pretreated substrate. Compared with SS pretreated straw, delignificationshowed less effect on cellulase adsorption to SC pretreated substrate. The maximum adsorptioncapacity of Langmuir adsorption could be improved with the increment of pretreatmentchemical charges for the pretreated solids.