Anaerobic co-digestion as a strategy for treating coffee Pulp: Insights into process performance

Coffee pulp (CP) is an energy-rich agro-industrial waste, but its treatment in anaerobic digestion is prone to digester instability. This study evaluated the performance and microbial dynamics of mono-digestion and co-digestion systems treating CP and cattle manure (CM) at increasing organic loading rates (OLRs). At 1.0 g volatile solids (VS) L^-1 d^-1, CP mono-digestion produced significantly higher methane yields than both CM mono-digestion and CP:CM co-digestion (4:1, VS basis), confirming its high energy potential under stable digester conditions. However, the methane yield substantially decreased in CP mono-digestion and CP:CM co-digestion systems at an OLR of 1.5 g VS L^-1 d^-1. Extending the retention time to 30 days yielded similar methane yields and methanogenic community profiles for both CP mono-digestion and CP:CM co-digestion. Specifically, the relative abundance of acetoclastic methanogens declined while hydrogenotrophic methanogens became more prevalent. This pattern suggests that feedstock-related inhibition favored hydrogenotrophic methanogenic pathways over acetoclastic methanogenesis. These findings underscore CP's high energy potential but also its sensitivity to elevated OLRs, emphasizing the need for strategies to counteract inhibitors.