Effects of biochar and microbial inoculum on maturity and greenhouse gas emissions during microaerobic composting of sheep manure

The livestock manure was effectively harmless and resourced by aerobic composting. However, during the aerobic composting process, a large amount of volatile gases are produced due to the isomerization of microorganisms, which is harmful to the environment and leads to serious loss of nutrients such as carbon and nitrogen, affecting the improvement of organic fertilizer quality. Therefore, it is necessary to adjust aerobic composting process parameters to reduce pollution gas emissions to fix carbon and nitrogen elements and improve maturity. Based on the previous research results, does the adjustment of ventilation rate to meet the normal oxygen demand of microorganisms help to degrade organic matter and reduce the emission of pollutants during composting? Based on this assumption, this study monitored compost maturity, gas emission and emission law by adjusting the low ventilation rate of 0.1 L/(kg·min) at the early stage of composting and setting intermittent ventilation mode and stopping ventilation at the late stage of composting. At the same time, biochar and microbial agents were added to strengthen the composting process. In order to investigate comprehensively the effects of exogenous materials (biochar addition and VT microbial inoculum) addition on maturity and greenhouse gas (NH3, CH4 and N2O) emissions during composting under low ventilation conditions. Three treatments were conducted in 60 L composting equipment for 42 days, pure sheep manure (CK) was set as control, which added with biochar (BC) and VT microbial inoculum (MC), respectively, as two treatments. In order to simulate the microaerobic environment, lower and intermittent ventilation rate was supplied during initial 14 days of composting, and stopped the ventilation in the rest of 28 days, Ventilation rate is 0.1 L/(kg·min). Results indicated that all treatments could meet the mature standard, such as germination index (GI)≥70%, pH≥8 and so on. Comparing with CK, BC and MC could improve GI by 27.8% and 38.8%, respectively, and prolonged the thermophilic phase to over 10 days, which satisfied the sanitation standard. Greenhouse gases discharged mainly in the first 14 days of composting, which was influenced by temperature, maturity and other physicochemical parameters. The addition of biochar and bacterial inoculum could reduce the total greenhouse gas emission. Comparing with the CK, the emission of NH3, CH4 and N2O from BC were reduced by 38.68%, 14.26% and 31.54%, and the total greenhouse effect was decreased by 31.11%. However, bacterial inoculum decreased NH3 emission by 18.41%, but increased N2O emission by 21.10%, and increased the total greenhouse effect by 20.70%. Therefore, In the microaerobic process of sheep manure, different exogenous additives have different effects on the emissions and laws of composting pollutants. Compared with microbial agents, biochar is a comprehensive additive that can be used in sheep manure microaerobic composting to improve compost maturity, accelerate degradation and humification of organic matters, reduce greenhouse gas emissions, increase the content of nutrition, as well as to provide theory references of sheep manure disposal in traditional heap composting, which is conducive to the promotion of microaerobic composting process. © 2022 Chinese Society of Agricultural Engineering. All rights reserved.