| 其他摘要 | Agricultural residues are attractive and potential feedstock for anaerobic digestion due to its abundance, low production costs, high polysaccharide content and methane yield. However, the efficiency of converting lignocellulosic biomass into methane is limited, which is attributed to not only the complex structure of corn straw but also the low activity and stability of the anaerobic microbial populations. So it is significative to pay attention to design and optimize the complex microbial consortia. Bioaugmentation is a technology for improving the removal of undesired compounds by introduction of specific competent strains or consortia. The basic premise for this intervention is that the metabolic capacities of the indigenous microbial community already present in the biotope slated for cleanup will be increased by an exogenously enhanced genetic diversity. Environmental friendly, energy saving and no any chemicals addition are the significant advantages of bioaugmentation. The method, application the bioaugmentation technology into the anaerobic digestion of straw, could accelerate the degradation of straw and improve production efficiency in condition of low consumption, no pollution and mild environment. This study mainly focused on the effect of the two exogenous, anaerobic enhanced bacteria on the mesophilic, methanogenic, anaerobic fermentation of untreated corn straw. Hydrogen producing acetate-type bacterium Acetobacteroides hydrogenigenes and benzoic acid degrading bacterium Sporotomaculum syntrophicum were found to have the bioaugmentation potential, according to the cumulative methane production. Then, the optimum inoculation ratios of the bacteria were determined through setting different inoculation ratios (5%, 10% and 20%). To investigate the functional mechanism of the enhanced bacteria on the degradation of corn straw, on the one hand, the composition of corn straw before and after digestion were studied, on the other hand, effect of the bacteria on anaerobic degradation of methyl cellulose, kraft lignin and xylan models were measured. Besides, nineteen types of environmental samples, which may have the potential for lignin degradation, were chosen as the initial system to domesticate efficient anaerobic lignin-degrading consortia. Details are as follows.
1. The bioaugmentation effect of Bacteroidetes bacterium A. hydrogenigenes on anaerobic digestion of corn straw was studied. A. hydrogenigenes is a hydrogen-producing acetate-type bacterium with a wide range of growth, substrate utilization, relatively high growth rate, high hydrogen yields, substrates and products tolerance. Bioaugmentation with A. hydrogenigenes could increase 19–23% methane yield from corn straw degradation. The maximum methane yield was 258.1 mL/g-corn straw with 10% inoculation. A. hydrogenigenes could improve the methane yields from methyl cellulose and xylan (models for cellulose and hemicelluloses, respectively) by 16.8% and 7.0%, respectively. A proposed mechanism is that A. hydrogenigenes promotes more hydrolysates of lignocellulosic biomass, such as C5 and C6 sugars to acetate and hydrogen. As a result, it provides a source of energy for the methanogens.
2. The bioaugmentation effect of benzoic acid degrading bacterium Sporotomaculum syntrophicum on corn straw anaerobic fermentation was investigated. S. syntrophicum in 5-20% inoculation ratios could improve the methane yield by 12-20%. The maximum methane yield was 252.2 mL/g-corn straw with 5% inoculation. S. syntrophicum increased not only the degradation efficiency of cellulose, hemicelluloses and lignin of corn straw by 10-13%, 3-5% and 38%, respectively, but also the methane production from methyl cellulose, xylan and kraft lignin models. A proposed mechanism is that S. syntrophicum could regulate the structure and activity of the indigenous flora, making it more adapt to fermentative environment.
3. Nineteen types of environmental samples, which may have lignin-degrading potential, were chosen as the initial system to domesticate efficient anaerobic lignin-degrading consortia with 0.1% (m/v) kraft lignin as the sole substrate. After two generations of culture, the culture from rice soil was the best among the remaining ten samples. It’s methane yield was 136.1 mL/g-lignin, and the kraft lignin degradation rate reached 9.9%. The characteristics of the culture will be determined in the next step. It hopes that apply the culture to the corn straw anaerobic fermentation system in order to increase the degradation of lignin. |
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