\textcopyright 2017 Elsevier Ltd Nopal (Opuntia ficus-indica (L.) Mill.) has the ability to grow in climatic conditions that are adverse for most conventional crops. It can be an alternative for biogas production by co-digestion with dairy cow manure, the second largest source of greenhouse gas emissions in dairy farms. To evaluate the feasibility of using nopal as a biogas source, the environmental impacts associated with the process need to be quantified. In this study, a life cycle assessment is carried out to evaluate the environmental impacts and energy balance of biogas production through co-digestion of nopal cladodes and dairy cow manure. A Baseline and three scenarios that had different farming systems and digestate storage management strategies were compared. Cropping system and direct field emission data were experimentally obtained from two plots using an organic farming system and a conventional farming system; biogas production and yield data were obtained in a 10-L anaerobic digester. Results indicated that the energy return on investment for biogas production ranged from 8.1 to 12.4. Organic farming system decreases the environmental impact by 22.5\% in the global warming potential category but increases the acidification potential and eutrophication potential impact category values by 47.2 and 45\% respectively, while covering the digestate tank results in a 2.3\% reduction in global warming potential and in a 1.7\% reduction in photochemical ozone creation potential. Based on these results, biogas production from nopal cladode and dairy cow manure co-digestion and digestate management offers cleaner energy production since the global warming potential has a lower value than that reported for similar feedstocks. The use of these two biomasses combines the strengths of a plant that accumulates biomass efficiently and the reduction of greenhouse gas emissions by using one of the main wastes in dairy production.
|Journal||Journal of Cleaner Production|
|State||Published - 2018|