Application of hyperthermophiles in sludge composting: a review

Sewage sludge treatment and disposal remains a challenging problem. Composting of sewage sludges is gaining increasing attention due to its cost-effectiveness, operation convenience, advantages in lifecycle management, and low greenhouse gas emissions. Disadvantages, such as long reaction time, significant land area occupation requirement, potential risks of residual heavy metals, and emerging contaminants, have restricted wider application. Here we review applications of hyperthermophiles in composting , focusing on the unique improvements provided by hyperthermophiles in composing temperatures, product safety, nitrogen preservation and humification. Inoculation of hyperthermophiles allows temperature of composting to reach over 80 °rees C. Specific metabolic strategies are critical in hyperthermophiles-inoculated composting. High-temperature resistance in the metabolism of hyperthermophiles and their roles in temperature rising during composting is often overlooked. This review discusses both aspects, allowing for a deeper understanding of the functions and influences of hyperthermophiles in sludge composting. Additionally, this review highlights the policy challenges associated with the hyperthermophiles-inoculated sludge composing technique and provides potential directions for future research in this field.