Phase-specific microbial relay strategy enhances lipid degradation and humification in aerobic composting of lipid-rich food waste

Lipid-rich food waste poses significant challenges in aerobic composting owing to oil-induced physicochemical barriers (>10 % oil content reduces porosity by 32–45 % and suppresses microbial activity). To bridge this gap, we designed a phase-specific microbial relay strategy integrating Pseudomonas aeruginosa DO1 with thermophilic consortia derived from agricultural soils (CK3). The results demonstrated that DO1 achieved 25 % lipid degradation within 96 h (mesophilic phase, <45 °C) through lipase secretion (121.18–131.45 U/mL) and enzymatic emulsification of lipids, after which its abundance decreased (from 26.99 % to 8.41 %). Subsequently, CK3-derived thermophilic bacteria (Bacillus, 38.54 %; Thermoactinomyces, 2.53 %) and fungi (Wallemia, 21.12 %) dominated the thermophilic phase (>50 °C for >5 d), driving β-oxidation-mediated lipid degradation to 91.91 % and enhancing humification with 92.74 % humic substances. Metagenomic analysis confirmed the enrichment of lipolytic pathways (ko00071, p < 0.01) and the upregulation of ammonia-assimilation genes (glsA/gdhB), reducing nitrogen loss to 25.1 %. This temperature-phased relay strategy enables the efficient in situ degradation of high-lipid waste (>15 % oil), offering a scalable solution for industrial composting.