The application of combined additives to enhance compost humification and carbon sequestration: Current status and...

Enhancing humification is a key strategy to increase carbon sequestration during composting, which also aligns with global carbon neutrality goals. However, traditional composting suffers from a number of challenges including prolonged humification cycle and a lower degree of humification. Additives, in particular the combined additives, are widely regarded as an effective and simple way to accelerate humification. So far, the effects of exogenous additives on compost maturity and microbial diversity have been well documented in previously literature. However, an in-depth review of the application of combined additives to improve humic substances and understand the synergistic mechanisms of humification pathway regulation is still missing from literature. This review innovatively summarizes the significant effects of combined additives on improving the humification process during composting. Compared with traditional composting, combined additives markedly decrease the emissions of CO₂ (by 12.2 %-36.8 %) and CH₄ (by 32.3 %-40.9 %) and increase the content of humic acids (by 26.7 %-133.3 %) and the degree of polymerization (by 13.8 %-100.0 %) during composting. The synergy of combined additives on compost humification are significantly influenced by the types and dosages of individual additives. The combination of biochar and microbial agent was found to be most effective for improving humic acids. Further research on the development of combined additives and the optimization of management practices for composting will improve the humification process in a sustainable and economic way.