Component-specific microbial degradation and humification mechanisms of typical kitchen waste during winter hyperthermophilic composting in northeastern China.

Kitchen waste (KW) is generated in enormous quantities, while conventional composting often performs poorly in winter because low temperatures suppress self-heating and biodegradation. Although hyperthermophilic composting (HC) can markedly promote KW degradation, the degradation mechanisms of specific KW components under cold-climate conditions remain insufficiently understood. A single-substrate enrichment strategy was established to compare the degradation of four representative fractions: cellulose, hemicellulose, lignin, and fats. After 30 days of composting, fat showed the highest degradation efficiency (49.51%), followed by cellulose (47.64%) and hemicellulose (45.29%), whereas lignin showed the lowest degradation efficiency (29.61%). Firmicutes played a dominant role across all four component-enriched systems. Tepidimicrobium was dominant in fat degradation, whereas Gracilibacillus and Ammoniibacillus were mainly associated with the degradation of cellulose, hemicellulose, and lignin. EEM-PARAFAC showed that aromatic proteins and soluble microbial by-products in all four systems were gradually transformed into humic-like substances, whereas lignin-derived dissolved organic matter showed weaker humification. Partial least-squares path modelling further indicated that hemicellulose and fat degradation were mainly driven by microbial activity, whereas cellulose and lignin degradation were more strongly influenced by environmental factors. These findings reveal component-specific microbial degradation and humification mechanisms during winter HC and provide a mechanistic basis for inoculum selection and process regulation for kitchen waste treatment in cold regions.