Physicochemical and percolating characteristics of sequencing batch dry anaerobic digestion of straw-cow manure mixture

The sequencing batch dry anaerobic digestion (SBD-AD) technology has advantages in large-scale treatment of agricultural wastes. SBD-AD project has the characteristics of large processing capacity of raw materials, high volumetric biogas production rate and less biogas slurry emission. Moreover, it is easy to operate and has low failure rate, and easy to handle agricultural solid wastes with high fiber content and difficult to degrade, such as crop straw, livestock manures. In the previous research, the key influencing factors of promoting methane yield were screened, the efficient control methods and operation processes were summarized, and the mechanism of methanogenesis was revealed. However, the mechanism of interaction between materials and leachate flow in dry fermentation process, especially the synergistic promotion of biogas production peak stage and biotransformation, needs further study. Therefore, the different dry fermentation systems were established based on the environmental factors of fermentation temperature and straw particle size, and the properties of dry fermentation, materials and leachate were explored by comparing the systems. In order to provide theoretical guidance for further improving the quality and operation efficiency of the SBD-AD, the relationship among material fermentation, structure and percolation fluid flow characteristics was established. In this paper, under the interaction of fermentation temperature and particle size, different dry fermentation environments were launched to compare biotic and abiotic characteristics, and to explore the fermentation mechanism, material morphology and leachate flow characteristics of improving mass transfer efficiency. The results show that changing the fermentation temperature and particle size of the straw can significantly promote the SBD-AD bioconversion efficiency (P<0.05), high temperature conditions make the straw degradation rate increased by 22.61% and accelerate the transformation of organic acid and ammonia nitrogen generating rate, the ultimate methane yield increased by 29.56%, straw particle size change can significantly promote the improvement of carbon conversion rate (P<0.05). In addition, straw particle size is the main factor affecting the material structure and the flow properties of leachate. Under the condition of short particle size, the total porosity decreases by 23.17% and the bulk density increases by 14.64%, and the water holding porosity and aeration porosity in the middle zone (inner zone) increase significantly, resulting in the outer area of leachate collection volume being 5.5 times and 10.8 times of that in the middle zone and inner zone. Under the condition of long particle size, the porosity of materials and the flow rule of percolate have no obvious change. Furthermore, the first 10 d of fermentation, material structure and the leachate flow characteristics tend to be stable, short particle size under the condition of leachate along the sides of their present material porosity from the center to the seepage rule, and long particle size significant difference (P<0.05), and the Clostridiales, Bacillales, Methanosarcina, Methanoculleus abundance was significantly positive correlation (P<0.05), which is the best state to promote biomass conversion efficiency. This study can provide a theoretical basis for evaluating and improving the operating efficiency of different SBD-AD systems. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.