Extended thermophilic phase promotes fungal-bacterial collaboration to facilitate humification in batch-fed composting.

Traditional composting is constrained by short thermophilic phases, which limit organic waste degradation and humification. This study investigated batch-fed composting (BFC) with extended high-temperature phases lasting up to 25 days to enhance microbial synergy and humic substance (HS) formation. Three treatments (K2: 2 kg/day, K3: 3 kg/day, and K4: 4 kg/day) were applied to determine the effect of feeding load on HS formation and compost maturity and elucidate the microbial mechanisms involved in fungal-bacterial synergy under sustained thermophilic conditions (45.2°C-63.1 °C). The results indicated that prolonged thermophilic conditions promote microbial interdependence, enabling fungal survival and activity despite high temperatures. K4 achieved the highest HS content (298.6 mg/g). However, K2 exhibited optimal maturity (germination index: 90 %) due to balanced humic acid/fulvic acid ratios (2.11), which contrasts with the increased phytotoxicity of K4. Structural equation modeling identified fungi as key drivers of HS regulators. Network analysis revealed microbial synergy (94 % positive interactions in K2), with fungi (e.g., Geotrichum) and bacteria (e.g., Bacillus) driving lignin depolymerization and humification. The study demonstrates that extended thermophilic conditions in BFC restructure microbial communities, enabling efficient lignocellulose degradation and humification. However, excessive feeding (K4) may compromise the reduction of phytotoxicity, highlighting a trade-off between HS accumulation and phytotoxic safety. These results advance sustainable food waste management by linking microbial dynamics to compost quality and provide actionable strategies to optimize feeding loads in BFC systems for high-quality compost production.