Study On Aerobic And Anaerobic Two-Phase Fermentation Process Design And Biogas Production Characteristic Of Rice Straw

It is statisticed that the total straw yield is about 890 million tons in 2012 and the collected resources is about 700 million tons, the yield of rice straw is about 200 million tons. A considerable part of the rice straw is used as firewood or returned to the farmland. The treated way not only wastes resources but also brings great environmental problems. The method of rice straw using anaerobic fermentation is environmental efficient and accorded the law of the nature. Rice straw contains about 60% above lignocellulose, owing to the physical shielding effect from lignin, hinder microbial cell extracellular enzyme contact cellulose and semi-cellulose, limit hydrolysis rate of cellulose and semicellulose, resulting in the anaerobic fermentation process is slow, the utilization of rice straw is low. Obviously, removing the lignin barrier is the primary step to improve the degradation rate of lignin in hydrolysis acidification. Lignin initial cleavage required the presence of molecular oxygen, without aerobic treatment lignin hardly degraded by microbes in anaerobic environment and the reproductive rate of aerobic microorganisms is much greater than that of anaerobic microorganisms. Therefore, put forward to aerobic and anaerobic two-phase fermentation process of rice straw. The process is divide into aerobic hydrolysis phase and anaerobic methanogenic phase, which aerobic hydrolysis phase takes gas supply measures to break the barrier effect of lignin before the methanogenic fermentation. Different cellulose degrading bacteria was added into the aerobic hydrolysis phase. The detected indicators mainly contain the activity of the enzyme, pH value, gas production, gas composition. By analyzing the data, the main results showed that:(1)Aerobic and anaerobic two-phase fermentation process has a significant effect on the removal of lignin barrier. Lignin degradation rate reached 4.57% but the traditional single phase anaerobic fermentation process lignin hardly occur. The degradation rate of cellulose and hemicellulose also changed significantly with Lignin degradation rate increasing. The cellulose degradation rate reached 50%,the cellulose degradation rate was increased20% compared with the single phase anaerobic fermentation. Substrate degradation rate of TS was also significantly increased, the TS degradation rate reached 63%, while the TS degradation rate of single phase anaerobic fermentation was only 44% and the degradation rate of TS was increased 20% compared with the single phase anaerobic fermentation.(2)Aerobic and anaerobic two-phase fermentation process has a significant effect on daily biogas production, cumulative biogas production, TS biogas yield and TS methane yield by comparing with single phase anaerobic fermentation. Cumulative biogas production reached 17000 mL in aerobic and anaerobic two-phase fermentation process but single phase anaerobic fermentation process was only 11000 mL. TS methane yield and VS biogas yield were also significantly higher than those of the control group. The highest TS biogas yield and VS biogas yield could be achieved 411.19 mL?g-1、450.97 mL?g-1 respectively, those were about 30% higher than the control group of single phase fermentation. TS methane yield of Aerobic and anaerobic two-phase fermentation process was about 246.63 mL·g-1,that reached 91.3% of the theory methane yield of the rice straw matter. The growth rate of TS methane yield was 36%.(3)The ability of different strains to produce various kinds of cellulase is different and cellulase is a kind of induced enzyme, the different growth environment will greatly affect the production of various kinds of cellulase and the degradation of cellulose activity, so the degradation rate of lignocellulose is different. The result showed that total enzyme activity of Trichoderma and Aspergillus niger mixed strains was higher than that of single strain and the highest group is mixed strains by aeration gas supply. It was accordance with the degradation rate of cellulose and hemicellulose. Cumulative methane production of mixed bacteria group was significantly higher than that of other groups, so Trichoderma and Aspergillus niger of two kinds of bacteria had no inhibitory effect.(4)the total enzyme activity ofthe treatment by the aeration gas supply was higher than others TS biogas production of the mixed strains by aeration gas supply reached 438.57mL·g-1, it was highest. It showed that aeration gas is more conducive to the growth of Trichoderma and Aspergillus niger mixed bacteria.