Environmental Assessment of a Waste-to-Energy Cascading System Integrating Forestry Residue Pyrolysis and Poultry Litter Anaerobic Digestion

Poultry and forestry waste residues, despite their environmental concerns, offer nutrient-rich content and wider availability. Utilising them in cascading approaches can create high-value products and establish new value chains in bioeconomy. This study aims to evaluate the environmental consequences of coupling forestry residue pyrolysis and poultry litter anaerobic digestion processes in a waste-to-energy cascading system. Moreover, a scenario analysis was conducted considering six scenarios with varying total solids loading with biochar (8%, 15%, and 28%) and final energy products (bioelectricity and upgraded biomethane). Life cycle assessment (LCA) results demonstrated a net reduction in selected potential impact categories across all scenarios, though with considerable variation in mitigation levels among them. Analysis revealed a major influence of selection of biogas utilisation pathway (electricity/biomethane) on overall impacts. The displaced processes such as natural gas contributed majorly towards the reduction in climate change and fossil depletion, whereas electricity grid mix contributed to terrestrial acidification and freshwater eutrophication. This study suggests that integrating pyrolysis and anaerobic digestion processes effectively valorises poultry and forestry residue waste, presenting a promising opportunity for promoting new value chains within Ireland's bioeconomy. This approach enhances bioresource utilisation, resulting in the production of value-added products with reduced environmental costs.