Anaerobic digestion of poultry litter - A consequential life cycle assessment.

Concentrated land spreading of poultry litter has the potential to cause nutrient build-up in soils, eutrophication of water bodies, air pollution and the spread of pathogens. As a result, alternative routes for the disposal of poultry litter are being sought. A consequential life cycle assessment was conducted to examine several scenarios where biogas produced from poultry litter is used to generate heat and electricity or is upgraded to biomethane which can substitute natural gas. For all of the scenarios considered in this study, diverting poultry litter to anaerobic digestion leads to reduced environmental impacts for global warming, fine particulate matter formation and terrestrial acidification. However, the extent to which environmental impacts are reduced varies significantly across the scenarios. Displaced processes including electricity or natural gas, peat moss production and avoided land spreading of litter contribute the most to reducing environmental impacts. Consequential life cycle assessment is a suitable tool to inform decision-makers about the impact of introducing a new multifunctional technology like anaerobic digestion when considering the systems which are displaced. The results show the range of potential environmental outcomes, rather than predicting a single most-likely outcome. The results of this study indicate that anaerobic digestion is a suitable disposal route for poultry litter which may lead to reduced environmental impacts. This type of analysis is recommended when considering alternative feedstocks and valorisation pathways in the circular economy.