Temperature-Driven Responses and Contributions of Hyperthermophiles: Linking Storage and Inoculation Strategies in Municipal Sludge Composting

Conventional aerobic composting is limited by incomplete organic matter degradation, long composting times, and low product quality. Hyperthermophiles have been applied in composting, but systematic studies on their storage conditions and inoculation strategies are lacking. In this study, the hyperthermophilic microbial consortium, designated as NJ, maintained higher post-storage regrowth capacity after 6-month storage at 25 °C and 4 °C than at −80 °C. Furthermore, inoculated at the medium-temperature stage, NJ enhanced organic matter decomposition and shortened the composting time by 50% compared with high-temperature stage inoculation (>55 °C). Compared with a commercial inoculant, NJ shortened composting time by 67%, increased the germination index from 70% to 85%,raised DTN by 40%, and led to humic substance accumulation by the end of composting, indicating improved product quality. Consequently, medium-temperature stage inoculation of NJ enhances composting efficiency and product quality by enabling earlier functional expression and effective ecological niche occupation.