Effects of biochar addition and wheat straw size on greenhouse gas emissions during the pig manure/wheat straw aerobic composting: based on pore structure and baterial communities

The change of porosity characteristics inside the reactor during aerobic composting is an important indicator affecting gas production and discharge, heat dissipation, microbial activity and organic matter degradation in the composting process. In recent years, biochar, as a porous substance, is often added to the aerobic composting process to reduce greenhouse gas emissions during the composting process and improve the microbial biochemical environment. However, the effect of wheat straw-based biochar as an additive on the change of pore characteristics of the reactor and its influence on the greenhouse gas emission and microbial activities in the aerobic composting process are unknown.In this study, wheat straw-based biochar pyrolyzed at 500 celsius was used as an additive to explore the effects of pore characteristics on greenhouse gas emissions and microbiota during aerobic composting of pig manure. In this paper, four groups of pig manure/wheat straw aerobic composting experiments were designed and carried out (Group A used a mixture of swine manure and 1-3 cm wheat straw without the addition of biochar; Group B used the same mixture with the addition of biochar; Group C used swine manure and wheat straw less than or equal to 0.6 cm without the addition of biochar; and Group D used the same mixture as Group C with the addition of biochar.), monitoring and analyzing the changes of basic physical and chemical parameters and the dynamic changes of CO2, CH4, NH3 and N2O gas production and discharge during composting; Based on micro-computed tomography, Micro-CT to characterize the local three-dimensional characteristics at the reactor scale, and analyze the pore changes of each group. High-throughput sequencing was used to further explore the functional succession mode of bacteria in the aerobic composting process of pig manure. The results showed that the C/N of the biochar group was higher than that of the biochar group, and the straw length had little effect on the C/N. Biochar as an additive can inhibit the formation of methane in dense piles. Long straw treatment can improve the pore characteristics of the pile, while the addition of biochar treatment will make the pore characteristics more complex. The pore characteristics inside the reactor reflect the macroscopic oxygen permeation, which affects the activity of anaerobic bacteria. The addition of biochar treatment increased the relative abundance of Proteobacteria and Actinobacteriota flora. Through RDA analysis, it was found that the pore characteristics had a relative influence on the distribution of microflora in each group, and the composting process increased.Exploring the pore characteristics of aerobic compost compost body of biochar as an additive provides a theoretical basis for greenhouse gas emission reduction.