Biological Pretreatment of Cynodon sp. Using Trametes hirsuta: Influence on Enzymatic Activity and Anaerobic Bioconversion

Garden pruning waste from Cynodon sp. is a lignocellulosic resource with high lignin content, which limits anaerobic digestion efficiency. While white-rot fungi can delignify biomass through solid-state fermentation (SSF), their efficacy depends on balancing lignin removal with preservation of fermentable carbohydrates. This study evaluated the effect of SSF times (8, 21, and 36 days) with Trametes hirsuta on enzymatic activity and subsequent biogas production. Laccase activity increased progressively, reaching 983.84 U/L at 36 days; whereas manganese and versatile peroxidases peaked at 21 days. Fungal-pretreated samples exhibited lower methane yields, a maximum of 225.32 NmL/gVS at 8 days, compared to untreated biomass (381.66 NmL/gVS). Total lignin content apparently increased across treatments, suggesting pseudo-lignin formation during autoclave sterilization, while glucose and xylose decreased. Biological pretreatment affected methane production by reducing sugar availability, potentially forming inhibitory furanic compounds and antimicrobial metabolites, thereby negating the benefits of enzymatic delignification. These results underscore the complexity of optimizing fungal pretreatment and highlight the need to balance fermentation time to preserve carbohydrates while modifying lignin structure.