Improving biogas production from spent coffee grounds via photocatalytic pre-treatment in comparison with UV photolysis

Spent coffee grounds (SCG) are a significant organic waste with potential for energy recovery in anaerobic digestion. However, their processing is limited by their high lignin content and complex lignocellulosic structure. This work aimed to compare photolytic and photocatalytic pre-treatment of SCG. Changes in lignocellulosic composition, particle morphology, and biogas production were evaluated. Photocatalytic pre-treatment was performed under UV radiation in the presence of a TiO 2 photocatalyst. This pre-treatment caused significant reduction in lignin content. SEM analysis confirmed a significant disruption of the biomass structure. These modifications were associated with an approximately 23% increase in biogas production and a 16% increase in methane yield. Furthermore, photocatalytic treatment reduced the caffeine content of the substrate. Photolytic pre-treatment, which took place under UV radiation without a catalyst, did not significantly affect lignin content, biogas production, or methane yield. This method thus increases the energy valorisation of coffee waste while reducing the risk of caffeine being released into the environment as a micropollutant.