Fungal pretreatment of yard trimmings for enhancement of methane yield from solid-state anaerobic digestion

Yard trimmings were pretreated by Ceriporiopsis subvermispora, a white-rot fungus that selectively degrades lignin, to enhance methane production via solid-state anaerobic digestion. Effects of moisture content (MC), at 45%, 60%, and 75%, on the degradation of holocellulose and lignin in the fungal pretreatment step and on methane production in the digestion step were studied with comparison to the control group (autoclaved without inoculation) and raw yard trimmings. It was found that C. subvermispora had a high lignin degradation of 20.9% but limited cellulose degradation of 7.4% at 60% MC. Consequently, samples pretreated at 60% MC achieved the highest methane yield of 44.6 L/kg volatile solid (VS) in the digestion step, which was 106% and 154% higher than the control group (21.6 L/kg VS) and the raw yard trimmings (17.6 L/kg VS), respectively. The increase in methane production was probably caused by the degradation of lignin during the pretreatment.