Humic substances and its electron transfer capacity during composting: A review

Humic substances (HS) are important product during composting, which play a key role in the maturity of compost, and its electron transfer characteristics have significant applications in the reduction of pollutants. We focus on the structure and composition characteristics and formation mechanism of HS during the composting. The effects of composting raw materials, additives, microorganisms and oxygen supply conditions on the formation of HS were reviewed. The electron transfer mechanism of compost HS was summarized as well as the structural and environmental factors affect the electron transfer of HS. The applications of HS in soil pollution control and water treatment are introduced. The research directions of HS formation mechanism, electron transfer mechanism and its application are also prospected.