Anaerobic digestion pathways and policy for low-cost CO2e mitigation on livestock facilities

Manure anaerobic digesters are typically funded by the amount of renewable fuel they produce and marketed by the amount of CO 2 e emissions they mitigate. Nonetheless, manure anaerobic digesters do not need to be excellent renewable fuel producers to be excellent CO 2 e emission mitigators. This study analyzes anaerobic digestion policy and pathways to investigate methods to expand the biogas industry and reduce livestock facility CO 2 e emissions. We assessed thirteen dairy farm sizes ranging from 100 to 10,000 head and fourteen swine farm sizes ranging from 1200 to 50,000 head to determine the necessary herd sizes for economically viable covered lagoon anaerobic digesters, heated anaerobic digesters, and heated anaerobic digesters with a covered effluent storage. We modeled profitability and emissions associated with renewable natural gas production (RNG), electricity production, and biogas flaring. Current incentives favor RNG production on large farms, leaving most farms with unprofitable prospective anaerobic digester projects, limiting biogas growth in the US. Our results indicate that electricity production from biogas costs 15% to 70% less than RNG per unit of CO 2 e mitigated. Additionally, a scenario analysis of Iowa suggests that an eRIN credit, worth the same value as a D3 RIN credit, would enable feasible biogas to electricity projects on over 90% of Iowan dairy and swine farms. Biogas to electricity projects and biogas flaring projects reduce livestock facility CO 2 e at reduced cost compared to biogas to RNG systems, however current electricity and flaring incentives struggle to support the biogas industry.