LCA-based carbon footprint analysis of anaerobic digestion of coffee husk waste

Abstract

While studies have shown that anaerobic digestion (AD) with energy generation of agricultural residues have many benefits, it is still unclear the extent to which this technology can reduce greenhouse gas (GHG) emissions, particularly in the context of coffee husk wastes. To address this knowledge gap, this work explored three scenarios of coffee husks as an energy source: 0) business-as-usual (landfilling); 1) AD with energy generation; 2) same as the previous one, adding a hydrothermal hydrolysis pre-treatment step. The study adopted a Life Cycle Assessment (LCA) methodology to estimate the environmental impacts of this technology in terms of GHG emissions. The results indicate that the main benefit of using AD is to avoid the impacts of landfilling, as the carbon footprint for the landfilling scenario was more than 13 times higher than the others. The emissions from digestate management were the main source of the overall emissions, accounting for 34 %. However, its use to replace chemical fertilizers affected the environmental performance positively. The inclusion of the pre-treatment was a key factor in making the bioenergy from coffee husks less carbon-intensive than natural gas and oil, although common renewable sources such as wind and hydropower tend to have lower GHG emissions. Sensitivity analyses indicate that this type of bioenergy can mitigate GHG emissions from energy generation in coffee-producing countries with fossil-based energy mixes. Overall, this work fills a knowledge gap by providing empirical evidence to the potential benefits of using coffee husks in the world's transition to a low-carbon economy.