Using life cycle assessment to determine the environmental interest of the treatment of organic effluents by anaerobic digestion with regard to territorial constraints

Abstract

The management of organic waste is a territorial issue and especially in Brittany because of the existence of nitrogen excess inducing a significant deterioration of surface water used for drinking water production and a green algae bloom on the coast under certain conditions. Collective management of organic waste by anaerobic digestion allowing nitrogen export represents a possible way to locally reduce the nitrogen pollution. In order to provide evidence of the environmental performance of this alternative, a Life Cycle Assessment (LCA) was carried out for three scenarios on the management of livestock effluent and food industry waste for a watershed in Brittany: a reference scenario representing current practice and two alternative scenarios with a post-treatment of the composting allowing the use of the biogas produced from anaerobic digestion either by a local industry or for an evapo-concentration process. Only three relevant environmental impact categories were assessed: climate change, acidification and eutrophication. The scenario with composting highlights the interest of biogas recovery. The scenario with evapo-concentration is the least impacting but leads to a potential impact transfer for eutrophication, due to the export of a significant amount of nitrogen out of the studied watershed. LCA is insightful for collective thinking but also opens the debate on these complex territories that watersheds are: should we favour a local collaboration to move towards industrial ecology and probably facilitated social acceptance, or encourage the reduction of the nitrogen pressure into a watershed in litigation?