Evaluating the full life cycle of the mixed-flow box and silo composting for livestock and poultry manure

Decentralized composting can be optimized for livestock and poultry manure in rural areas. In this study, the life cycle assessment (LCA) and life cycle costing (LCC) approaches were employed to compare the environmental, economic, and social performances of two composting reactor models: the mixed-flow box and the silo system. A systematic evaluation was made on the synergistic mechanisms between economies of scale and low-carbon technologies, as well as the alignment pathways between technological choices and regional development needs. The sustainable management of the rural waste was aligned with the carbon neutrality goals, resource recycling, and rural revitalization. In the environment, the mixed-flow box exhibited a significantly lower standardized total environmental impact potential (-0.106) than the silo system (-0.013), indicating a stronger overall environmental benefit. The reason was that the solar-assisted design reduced the fermentation electricity consumption by 56%, leading to notable reductions in the climate potential, fossil depletion, and ecotoxicity categories. Midpoint impact analysis was performed on the 18 key indicators. It was found that the mixed-flow box shared the lower contributions to the human toxicity, particulate matter formation, and freshwater eutrophication. Contribution analysis further revealed that the production and use phases also exerted less pressure on the environmental systems, compared with the silo. In terms of economic performance, the silo system demonstrated greater profitability and financial feasibility, due to its scale advantages. The silo achieved a unit economic benefit of 79.01 CNY/t, which was 8.4 CNY/thigher than the mixed-flow box. The mixed-flow box and silo composting also exhibited significant differences in the energy consumption structure. The operational electricity consumption of the mixed-flow reactor was only 26.1 kW·h/t, accounting for approximately 41% of that of the silo system (63.8 kW·h/t). Financial indicators showed a net present value (NPV) of 1.9344 million CNY, an internal rate of return (IRR) of 13.04%, and a dynamic payback period (DPP) of 7.82 years. These values were well above the national benchmark discount rate (4.9%), indicating the investment attractiveness for the medium-to-large-scale rural projects. Social performance analysis indicated that the mixed-flow box offered 2.7 times more employment opportunities per unit investment than the silo, indicating a more effective approach for poverty alleviation and inclusive development in the labor-rich rural areas. However, the silo-related jobs provided higher monthly wages than the job quality in the low-wage mixed-flow systems. Some recommendations were proposed to balance the job quantity and quality, including the government subsidies to the poverty reduction metrics, such as the hiring ratios of the low-income households, and the employment quotas, as seen in international practices like India’s “Green Job Quota” scheme. In conclusion, the mixed-flow box is more suitable for the decentralized deployment in the small village communities with the dispersed manure generation, limited infrastructure, and greater labor availability. In contrast, the silo system is more appropriate for the centralized operations in townships or cooperatives for the greater economic returns and process standardization. Solar energy and intelligent aeration technologies can be integrated to reduce the energy consumption for high composting efficiency and performance. Overall, this finding can provide a systematic evaluation of two composting technologies from a multi-dimensional sustainability perspective. The actionable guidance can provide solutions for the localized manure treatment for environmental sustainability, economic viability, and rural social development in modern agriculture.