| Recent years, to reduce the reliance on fossil fuels, governments have initiated the extensive research into the renewable energies. The breakdown of plant lignocellulose to glucose monomers is the basis for second-generation cellulosic bio-ethanol production. The lignocellulose consists of three basic chemistry components of cellulose, hemicellulose, and lignin, whose conversion to ethanol employs three major steps:pretreatment, enzymatic hydrolysis, and fermentation. Due to the robust structure of lignocellulosic biomass, the efficiency of conversion is low indeed. So pretreatment is a prerequisite for enzymatic hydrolysis into fermentable sugars to be completed within an industrially acceptable time frame.The typical pretreatment methods, such as acid, alkali, and steam explosion, have some disadvantages in the commercialization of lignocelluloses conversion, including inefficiency, special equipment requirements and a lot of energy consumption. To overcome these obstacles, a stepwise pretreatment of combination of bacterial treatment with chemical treatment was conducted to enhance enzymatic hydrolysis of rice straw. The technical parameters and functional mechanism of combination pretreatment were studied by measuring the key indicators containning the composition, organization structure, surface morphology and enzymatic hydrolysis efficiency of the rice straw. The new design of combination pretreatment performed well at simplifying the requirements of equipment, lowering cost and/or increasing efficiency and employing easy process to follow, which accords with the principle of lignocellulose pretreatment and the request of industrialized application.In this study, a lignocellulose degrading bacterial strain LD-1 were isolated from pulp paper mill effluent sludge, which showed potential of lignocellulose pretreatment. Combining this bacterial strain pretreatment with NaOH/Urea pretreatment, The rice straw was dealt by LD-1, and then treated with NaOH/Urea, achieving a method of rice straw pretreatment. The results showed that biological treatment with a bacterium Sphingobacterium sp. LD-1 achieved mild conditions for the sequential NaOH/Urea treatment, obtaining an obvious enhancement on enzymatic hydrolysis. The research findings and conclusions of this paper are as follows:(1) LD-1 showed homology to Sphingobacterium and Bacillus, and the the strain was finally designated as Sphingobacterium sp. LD-1. Under the appropriate culture conditions (10% inoculum, pH=7, at 30?, shaker spade at 120 rap/min), the LD-1 degraded 50.4%,46.8%,49.58% of cellulose, lignin and hemicellulose, respectively, after 5 days incubation, which showed relatively high degrading ability of lignocellulose.(2) The 9.25 mg·ml-1 of reducing sugar and 5.98 mg·ml-1 of glucose were obtained under co-treated with LD-1 and 4%/6% NaOH/Urea at-10?, which increased 6.35 and 6.49-fold compared to untreated sample.(3) In the stepwise pretreatment, the biological treatment with a bacterium Sphingobacterium sp. LD-1 achieved mild conditions for the sequential NaOH/Urea treatment, reducing the concentration of the NU solution from 7%/12% to 4%/6% and increasing the temperature from 20? to 10?, indicating that synergistic effect existed in the stepwise pretreatment.(4) After the combination pretreatment, the chemical composition of rice straw had changed significantly. The content of lignin reduced to 7.7% from 12.7% and hemicellulose decreased from 20.4% to 14.2%,whereas the cellulose content increased to 69.7% from 51.7%, which indicated that this combination pretreatment had significantly delignification to enhance the enzymatic hydrolysis of rice straw.(5) The results of SEM, FTIR, XRD and TG analysis showed that the combination pretreatment could increase the porosity and surface area of biomass substrate, isrupt the robust structure and reduce the crystallinity to enhance the initial adsorption of enzyme and reactivity of cellulose in the saccharification so the enzymatic hydrolysis was improved significantly. |
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