Life cycle environmental sustainability of valorisation routes for spent coffee grounds: From waste to resources

Spent coffee grounds (SCGs) have a potential to be used as a feedstock for higher value-added products, such as biodiesel. However, the environmental implications of the valorisation of SCGs are largely unknown. This study evaluates the life cycle environmental impacts of utilising SCGs for biodiesel production in comparison with the widely used disposal of SCGs as a waste stream: incineration, landfilling, anaerobic digestion, composting and direct application to land. The scope is from cradle to grave and the functional unit is defined as 'treatment of 1 tonne of SCGs'. The results show that the most environmentally sustainable option is incineration of SCGs, with net-negative impacts (savings) in 14 out of 16 categories, followed by direct application of SCGs to land with 11 net-negative impacts. Biodiesel production is the least sustainable option with the highest impacts in 11 categories, followed by composting. The paper also demonstrates that following various waste hierarchy and resource valorisation guidelines instead of a life cycle approach could lead to a choice of environmentally inferior SCG utilisation options. Therefore, these guidelines should be revised to ensure that they are consistent and underpinned by life cycle thinking, thus aiding sustainable resource management in a circular economy context.