Transformation Characteristics of Organic Carbon at Different Molecular Weight Fractions During Food Waste Composting

Food waste is commonly valorized through aerobic composting, yet the responses of water-soluble organic carbon (WSOC) across molecular-weight (MW) fractions remain insufficiently resolved. This study aimed to quantify how distinct composting strategies regulate WSOC MW distribution and compositional evolution and identify the key physicochemical drivers. Food waste was treated by 30-day conventional composting (CK), 15-day phased inoculation (JJ; 2% (w/w) antioxidative consortium dominated by Bacillus/Pseudomonas followed by 2% (w/w) thermophilic cellulolytic consortium enriched in Geobacillus/Paenibacillus when the temperature reached 50 °C), and 24-h rapid thermophilic composting (RC; 2% (w/w) inoculation with a 24-h moist-heat pretreatment). RC yielded a small molecular weight organic carbon (SMOC)-rich product with low aromaticity, with MW < 5 kDa accounting for 68.21% (MW < 500 Da: 28.50%). JJ preferentially enriched more oxidized, fulvic-like/carboxyl-rich organics, increasing the fulvic-like contribution from 15.97% to 35.40% and raising the HMOC/SMOC to 2.72:1. CK showed the strongest humification, with MW > 5 kDa reaching 65.56% and humic-like Region V increasing from 26.25% to 66.36%. pH was the primary predictor of MW (day 6: CK 3.9; JJ 4.9; final ~8.8), while temperature jointly governed humic-like formation in RC.