Introducing the Farm Energy Analysis with Anaerobic Digestion (FEAAD) tool: Insights into farm-level energy, economic, and environmental analysis with comparative case studies

Agriculture faces increasing pressure to reduce greenhouse gas emissions and manage nutrients sustainably. On-farm anaerobic digestion offers an option to generate revenue, improve circularity, and reduce greenhouse gas emissions, but its success depends on the complex interactions between the cropping, livestock, and energy systems. This paper introduces the Farm Energy Analysis with Anaerobic Digestion (FEAAD) tool, an open-source, spreadsheet-based model designed to provide an evaluation of integrated farm management systems and scenarios. FEAAD provides users with an analysis of the farm-level life cycle greenhouse gas emissions, nutrient (nitrogen, phosphorus, and potassium) cycling, energy balances, and economic returns specific to Pennsylvania and Iowa agronomic conditions. We demonstrate the capabilities of the tool through two comparative case studies: a Pennsylvania dairy and an Iowa beef farm, both containing OFAD systems with different end-use cases. In both scenarios, anaerobic digestion transformed the farms from net energy consumers to producers and reduced farm-level global warming potential by 28 - 60%. However, the analysis revealed important trade-offs. For example, while co-digestion with food waste or herbaceous feedstocks can increase energy production, it may also exacerbate nutrient accumulation and methane emissions from digestate storage. Understanding these relationships and trade-offs is crucial for developing sustainable agricultural systems. FEAAD provides a useful decision-support framework for researchers, farmers, and other stakeholders to analyze and better understand these trade-offs.