Energy and environmental trade-offs in anaerobic digestion: Batch tests and LCA investigations of giant hogweed, canola straw, and manure

This study investigated the energy and environment trade-offs of anaerobic digestion (AD) using invasive giant hogweed, agricultural residue canola straw, and cow manure by combining mesophilic batch tests with a gate-to-gate life cycle assessment (LCA). Seven scenarios, comprising both mono-digestion and co-digestions were evaluated. Mono-digestion of Giant Hogweed achieved the highest specific biogas yield (671 L_N/kg VS) and methane content (74.7%), with no detectable hydrogen sulphide (H₂S), while co-digestion introduced mix-dependent trade-offs between gas yield and emissions. The LCA identified the combined emissions from manure and digestate storage as the primary hotspot for Global Warming Potential (GWP), contributing 53-67% of total emissions. Crop-based mono-digestion scenarios exhibited higher GWP per tonne but lower emissions per kWh due to superior energy recovery; the same pattern held for abiotic depletion (fossil and elements). Sensitivity analysis showed that a 50% cut in storage emissions reduced GWP by 27-34% across all scenarios. Scenarios with higher net electricity output achieved lower impact intensities per kWh. The study concludes that optimizing feedstock ratios and implementing advanced storage practices is critical for maximizing both energy recovery and environmental performance of AD systems.