Scaling sustainable pig manure treatment: Life cycle assessments for small to large piggeries in China

Over 50 % of pig stockpiling and slaughtering in China is attributed to medium and large piggeries. The diverse scales and distributions of these piggeries present significant challenges for the sustainable management of pig manure, with a research gap in assessing the environmental benefits of treatment technologies across different farm sizes. Therefore, the environmental and economic performances of ten pig manure treatment technologies for small, medium and large piggeries were evaluated via life cycle assessment and life cycle costing methods. The black membrane biogas pool (BMBP) technology for medium-scale piggeries demonstrates superior environmental performance, reducing emissions by 44.00 kg CO2 equivalent, 0.36 kg SO2 equivalent, and 0.05 kg PM2.5 equivalent per ton of dry pig manure treated. Additionally, the products generated from this process can offset 2.93 GJ of energy consumption and 0.25 tons of water consumption. Meanwhile, the ectopic microbial fermentation bed technology provides the best economic efficiency, at the cost of only $17.88 per ton. Significant disparities in the scale of piggeries and manure production across provinces necessitate region-specific policies. The estimated global warming potential (GWP) from pig manure treatment nationwide was 5.31 million tons of CO2 equivalent, with Henan, Sichuan, and Hunan provinces accounting for a combined 28.3 % of this total in 2020. Scenario analysis indicates that by 2025, achieving a pig manure utilization rate of 90 % could reduce GWP by 9.1 % (0.5 million tons of CO2 equivalent) compared to an 80 % utilization rate, with reductions ranging from 1.78 % to 22.36 % across other environmental indicators. Promoting technologies such as BMBP and transitioning 5 % of aerobic processes to anaerobic processes could reduce emissions by 2.9 %, while also lowering other environmental indicators by 12.8 % to 20.1 %. The utilization of anaerobic technology, coupled with enhanced utilization rates, can prove more efficacious in mitigating carbon emissions and pollutants.