Optimizing Phosphoric Acid Plus Hydrogen Peroxide Pretreatment On Wheat Straw For Enzymatic Hydrolysis And Fermentation At High Solid Loading

The production of bioethanol mainly involved three processes:pretreatment,enzymatic hydrolysis and fermentation.In this paper,a new pretreatment method-phosphoric acid plus hydrogen peroxide?PHP?was used to pretreat wheat straw.Based on the technological process of bioethanol production,the optimal conditions of PHP pretreatment and enzymatic saccharification and fermentation?SSF?at high solid loading were investigated for providing a reference for bioethanol production by using PHP pretreated wheat straw.The main results were as follows:?1?During the optimization of PHP pretreatment,temperature,H₃PO₄ concentration and time for pretreatment was investigated using Box-Behnken Design response surface method.And analyzed the response of pretreatment conditions to cellulose recovery,hemicellulose removal,lignin removal,cellulose-glucose conversion and glucose yield.Results indicated hemicellulose and lignin removal positively responded to the increase of pretreatment temperature,H₃PO₄ proportion and time.H₃PO₄ proportion was an important variable to control cellulose recovery,followed by pretreatment temperature and time.Moreover,these 3 variables all negatively related to cellulose recovery.Increasing H₃PO₄proportion can improve cellulose-glucose conversion,however,reduced cellulose recovery resulting in decrease of glucose yield.Extra higher temperature or longer time for pretreatment was not beneficial to cellulose-glucose conversion and glucose yield.Based on the criterion for maximizing cellulose-glucose conversion and glucose yield,the optimized pretreatment conditions were 40.2°C,2.9 h,and H₃PO₄ concentration of 79.6%,by which cellulose-glucose conversion reach 90%,glucose yield was 244 mg/g wheat straw after 48h enzymatic hydrolysis.Besides,the maximal glucose yield?299 mg/g wheat straw?can be reached after 72 h enzymatic hydrolysis by using PHP pretreated wheat straw in condition of 40°C,2.0 h,and H₃PO₄ concentration of 70.2%.?2?Based on the optimal PHP conditions,the pretreated wheat straw was investigated for cellulose-glucose conversion at high solid loadings.Results indicated solid loading could reach 20%with 77.4%cellulose-glucose conversion and glucose concentration of 164.9 g/L in hydrolysate,it even was promoted to 25%with only 3.4%decrease on cellulose-glucose conversion as the pretreated wheat straw was dewatered by air-drying.72.9%cellulose-glucose conversion still was achieved as the minimized enzyme input of 20 mg protein/g cellulose was employed for hydrolysis at 20%solid loading.In the corresponding conditions,100 g wheat straw can yield 11.2 g ethanol with concentration of 71.2 g/L by simultaneous saccharification and fermentation.Thus,PHP pretreatment benefitted the glucose or ethanol yield at high solid loadings with lower enzyme input.Additionally,decreases on the maximal cellulase adsorption and the direct-orange/direct-blue indicated drying the PHP pretreated substrates negatively affected the hydrolysis due to the shrinkage of cellulase-size-accommodable pores.?3?According to the characteristics of enzymatic hydrolysis at high solid loading by using PHP pretreated wheat straw in the optimal condition,the pretreated wheat straw was fermented?SSF?on different solid loading,enzyme input and yeast input.The results showed that solid loading of PHP-pretreated wheat straw can be greatly promoted to 20%.More enzyme input improved ethanol conversion significantly,but it still can be potentially reduced to 10-20 mg protein/g cellulose.Excessive higher or lower yeast input was not benefit for SSF.The proper yeast concentration of SSF was 1-2 g/L.Therefore,the optimal conditions of SSF was determined by using Box-Behnken Design response surface method.As minimization of enzyme and yeast input in SSF,and simultaneous maximization of ethanol conversion and ethanol concentration,the maximal ethanol conversion of 88.2%and ethanol concentration of 69.9 g/L could be achieved after SSF 120 h at solid loading of15.3%,CTec2 enzyme input of 13.2 mg protein/g cellulose and yeast input of 1.0 g/L.In this condition,15.5 g ethanol can be produced from 100 g wheat straw.