Mechanistic insights into humic acid formation from lignocellulosic waste via aerobic composting: A review

Aerobic composting of lignocellulosic waste is a key strategy for resource recycling, with humic acid (HA) formation being a central outcome of this process. This review systematically examines the mechanisms underlying HA synthesis, emphasizing the synergistic roles of biotic and abiotic pathways. Key findings reveal that microbial communities, particularly functional microorganisms like White-rot fungi and Actinomycetes, drive lignocellulose degradation and precursor aggregation through enzymatic actions and quorum sensing mechanisms. Abiotic factors, including metal ions, pH, and temperature, further regulate the humification process by influencing reaction pathways and efficiency. Optimization strategies, such as process parameter regulation and exogenous additives, significantly enhance HA yield and quality. The review highlights that HA formation occurs via multiple interconnected pathways, including the polyphenol, microbial synthesis, cellular autolysis, and Maillard reaction pathways, each contributing uniquely to humification. Advanced technologies like microbiomics and proteomics have elucidated microbial regulatory mechanisms, while the catalytic functions of key enzymes and metal ions have been identified as critical for HA polymerization. This comprehensive analysis provides theoretical and practical insights into improving humification efficiency, offering valuable guidance for the resource utilization of lignocellulosic waste in sustainable agriculture and environmental management.