Enhancing humification in high-temperature composting: Insights from endogenous and exogenous heating strategies

Livestock manure is difficult to manage for high moisture and nutrients. High-temperature composting (> 75 °C) reduces moisture. However, the humification process, crucial for nutrient recycling, remains poorly understood. This study investigated the humification mechanisms of endogenous-heating hyperthermophilic composting (HC) and exogenous-heating continuous thermophilic composting (CTC). Both methods significantly increased humus by 258.70 % in HC and 193.93 % in CTC. Spectral analysis showed stronger humification in the early stage for HC and in the later stage for CTC. Microbial activity primarily drove humification in HC, while environmental factors had more influence in CTC due to its simpler microbial structure. These results suggested that the polyphenol pathway, involving quinones and protein condensation, dominates humification in HC, while the Maillard reaction, with sugars and protein aggregation, dominates in CTC. Humification can be enhanced by increasing protein in HC and sugar in CTC. These findings provided strategies to improve humification efficiency and promote sustainable agriculture.