Alternatives for the energy reuse of coffee husk waste : an LCA based carbon footprint analysis.

Abstract

As the biggest coffee producer in the world, one of the most readily available renewable energy sources in Brazil is biomass, more specifically, coffee husks, the solid waste of coffee processing. However, this resource is still little used and there is not enough information in the literature about its environmental aspects. Due to the amount of this residue, the sustainable management of such residues is a growing concern. Emerging options for sustainable management of coffee husks include the anaerobic digestion and energy generation using agricultural waste as feedstock, and several studies have shown the great potential benefits, such as reducing the impacts of waste management, decreasing greenhouse gas (GHG) emissions and helping the country achieve its goals in the Paris Agreement. Life Cycle Assessment (LCA) is an environmental tool widely used around the world to assess environmental impacts in value chains. When an LCA study quantifies the direct and indirect GHG emissions of a product, its carbon footprint (CF) is calculated. This work compared coffee husk landfilling to two energy generation scenarios using anaerobic digestion, one of them including a hydrothermal hydrolysis pre-treatment of the husks. The results point to the fact that the main benefit of using anaerobic digestion to produce electricity is to avoid the impacts from the current management route of coffee husks, as the CF results for landfilling were over 13 times higher than the other scenarios. The emissions from digestate management, especially N2O volatilization on the soil, was the biggest contributor to the carbon footprint, with over 34% of results. On the other hand, the use of digestate to replace chemical fertilizers affected the environmental performance positively, in terms of avoided impacts. The carbon footprint of the kWh generated in the pre-treated scenario is 72% lower than the crude coffee husks, but it is still higher than the footprint of the Brazilian grid. When compared to other types of energy, the inclusion of the pre-treatment was a determining factor to render the bioenergy from coffee husks more interesting from a GHG emissions perspective, but renewable sources such as wind and hydro still have a lower CF. However, in countries such as in Indonesia and Vietnam, where the grid is more heavily based on fossil fuels, coffee husks, especially with pre-treatment, showed potential mitigate the carbon footprint of energy generation.