Linking the electron transfer capacity with the compositional characteristics of dissolved organic matter during hyperthermophilic composting

Highlights: • The ETC and compositional characteristics of HA, FA and HyI in HTC were studied. • Compared with TC, HTC can significantly enhance the ETC of DOM. • The formation of quinone-like moieties contributed to the enhancement of EAC. • The degradation of tryptophan-like substances was conducive to enhancing the EDC. • PLS-PM revealed that the EAC of HA can be used as a maturity index for compost. Redox-active functional groups in dissolved organic matter (DOM) can mediate reductions in organic pollutants and the passivation of heavy metals, which are related to the humification process of composting. Hyperthermophilic composting (HTC) has been shown to promote changes in the composition and structure of DOM and accelerate humification. However, how HTC affects the redox properties of DOM remains unclear. Here, we fractionated DOM into humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) fraction to study their electron transfer capacities (ETC) and the relationship between ETC and compositional characteristics using electrochemical method and excitation-emission matrix-parallel factor analysis. HTC accelerated the formation of component 3 containing quinone-like moieties, which mainly existed in the HA, improving the electron accepting capacity (EAC) of DOM. The rapid degradation of component 4 containing tryptophan-like substances of HA, FA and HyI strengthened the electron donating capacity of DOM in HTC. Partial least squares path model also showed that compositional changes and the stronger ETC of DOM in HTC had a positive effect on the maturity degree, revealing that the EAC of HA could be used as a maturity index for compost. This study advances our understanding of the humification process and the contamination control mechanism of HTC.