Abstract:
China is a big agricultural country, which produces a lot of agricultural waste every year. With the improvement of China’s agricultural productivity, agricultural wastes such as straw and livestock manure are relatively concentrated, which creates appropriate conditions for the application of sequencing batch dry anaerobic digestion (SBD-AD) technology to produce methane. Sequential batch anaerobic dry fermentation is an important technology for large-scale processing of agricultural and rural wastes to produce clean energy. It has such outstanding problems as low decomposition rate of materials, high operating energy consumption, and uneven mass and heat transfer, which limit the increase in methane yield.In this study, by adjusting the dissolved oxygen concentration in the initial reactor of the fermentation, a microaerobic simultaneous pre-heating and efficient sequential batch anaerobic dry fermentation system was established to further study the self-heating, decomposition, intermediate product properties and key microbial communities. The mechanism of promoting material heating and methane production.The results show that the micro-aerobic speeds up the heating rate of the materials in the reactor, which is 27.12% higher than the un-aerated temperature; the temperature of methanogenesis can be maintained above 42.48 ℃ without relying on external heating. A small amount of aeration in the initial stage of fermentation significantly improved the conversion efficiency of intermediate products in the anaerobic fermentation process (P<0.05). The lignocellulose degradation rate was increased by 57.88% -85.53% compared with the non-aerated group; the sCOD concentration was increased by 74.67% compared with the non-aerated group. The concentration of ammonia nitrogen in the non-aeration group is increased by 31.95% compared with the micro-aeration group, and micro-aeration increases the conversion efficiency of ammonia nitrogen; in particular, the accumulation of propionic acid decreased by 82.63%. The concentration was consumed by 285 mg/L on the 33rd day, and the system pH value was always maintained at 6.8-7.5. After 7 days of micro-aeration, the cumulative biogas production gap gradually increased, and the methane output of the micro-aeration group increased rapidly. On the 5th to 15th days, it was a rapid period of methane production. Overall, the cumulative methane content in the aeration group was 1.5 tines of the non-aeration group after 60 days of fermentation, the cumulative biogas and methane production increased by 56.76% and 41.79%, respectively. Bacteria Bacteroidales, Clostridiales and archaea Methanosarcina, Methanobacterium are conducive to promoting microaerobic simultaneous pre-heating and methane production efficiency, and have a significant correlation with degradation rate and organic acid concentration. This study provides a theoretical basis for exploring the efficient engineering control process of the sequential batch anaerobic dry fermentation.