Environmental assessment of energy production from anaerobic digestion of pig manure at medium-scale using life cycle assessment

Abstract

This study assessed the potential environmental effects of energy production from pig manure treatment by anaerobic digestion at medium-scale based on the Life Cycle Assessment of a farm in Puebla, Mexico. It also compared the results from common practices of biogas flaring and conventional management. The analysis was based on one ton of pig manure in 4 systems: two with energy production, one with biogas flaring, and the last one conventional management. The use of biogas for electricity production combined with composting techniques generated the lowest net impacts on climate change of 272 kg CO₂eq and photochemical oxidation of 0.056 kg ethylene eq, while the biogas flaring registered impacts of 344 kg CO₂eq and 0.095 kg ethylene eq. The systems with energy production had environmental benefits on fossil resources depletion by avoiding the consumption of -863 MJ and -1608 MJ, but systems that burned biogas required fossil fuel consumption of 246 MJ from the grid. The conventional management generated the greatest environmental impacts, with eutrophication being the most important negative effect due to the manure discharge into water bodies (5.97 kg PO₄eq). Sensitivity analysis shown that energy production could generate greater impacts on global warming compared to the case in which manure was used directly in crop fields, if emissions from unintentional releases and a poor digestate management are not avoided. Results are relevant for developing countries in which processes are carried out in rural and semi-industrial areas with lack of technical knowledge and economic resources.

Keywords: Anaerobic digestion; Biogas flaring; Energy production; LCA; Medium-scale; Pig manure.