• Open-access life cycle inventory tool for future anaerobic digestion biorefineries. • Robust mass and energy balances for accurate nutrient tracking towards circularity. • Counterfactual processes included to capture full environmental effects. • Largest circularity potential via biofertiliser production with effluent irrigation. • Largest climate effects: methane slip, carbon capture, and counterfactual processes. Anaerobic digestion (AD) is central to most biorefinery concepts, as an enabler of nutrient cycling and energy recovery. However, the environmental performance of AD-biorefineries remains poorly represented in many life cycle assessment (LCA) studies, owing to complex flows and indirect effects - including diversion of waste streams and multiple pathways of biogas and digestate use. Using a novel, expanded boundary LCA model (LCAD2.0), we systematically demonstrate critical factors influencing the environmental sustainability and nutrient circularity of 150 prospective AD-biorefineries. Critical factors for climate effects are methane yield, the type of energy being substituted, fugitive emissions during biogas upgrading, the counterfactual treatment of waste, and the application of carbon capture and use or storage (CCU/CCS). Critical factors for nutrient cycling include feedstock composition, digestate upcycling, and nitrogen losses during digestate storage. This study provides robust evidence to facilitate the transition towards a climate neutral, circular economy based on AD-biorefineries.
Martínez-Arce et al. (Thu,) studied this question.