A Microbial Inoculum (PLC-8) Improves Composting of Spent Mushroom Substrate

Composting is a useful way to reduce and recycle agricultural and forestry waste; however, low-temperature environments can inhibit the microbial processes involved in composting. Spent mushroom substrate has a high lignocellulose content, making it particularly difficult to decompose. There is a need to explore methods for effectively promoting microbial activity and enhancing composting efficiency under low-temperature conditions. This study explored the use of C/N ratio adjustments and a microbial inoculum (PLC-8; comprising Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes, Basidiomycota, Ascomycota, and Cryptomonadales) to improve spent mushroom substrate composting in a low-temperature environment. The temperature, lignocellulose content, pH, and gas emissions were measured during composting, and the microbial community structure was determined to explore associations between biotic and abiotic factors. Compost piles with PLC-8 entered the high-temperature period in 25 days, which was 15 days earlier than the control pile. When the C/N ratio was adjusted to 30:1 and PLC-8 was applied, the cellulose and hemicellulose degradation rates after 60 days were 88.04% and 71.95%, whereas the control group only exhibited degradation rates of 25.39% and 35.64%. Moreover, PLC-8 significantly increased CH₄ and CO₂ emissions and reduced nitrous oxide emissions. Microbial community analysis showed that Proteobacteria and Ascomycota were the dominant phyla in the piles with PLC-8, and these phyla were responsible for lignocellulose decomposition and carbon metabolism.