Effect of MnO2 on biotic and abiotic pathways of humic-like substance formation during composting of different raw materials

Abstract The humic-like substances (HLS) are proposed to be formed by biotic and abiotic pathways. The abiotic pathways were neglected in existed composting studies. The present study aims to accelerate the abiotic pathways, and to investigate how MnO 2 drives the HLS transformation via changing the contribution of abiotic and biotic pathways during composting with different materials. Parallel factor analysis model (PARAFAC), hetero two-dimensional correlation spectra (hetero-2DCOS) and variance partitioning were used to identify the effects of MnO 2 on the formation of humic acid (HA) and fluvic acid (FA) during composting of chicken manure (CM) and corn straw (CS). The addition of MnO 2 could change the structures of HLS during CS and CM composting, mainly promoting the formation of complex components in HA and FA during CS composting, as well as the complex components of FA during CM composting. Meanwhile, the addition of MnO 2 could reshape the microbial ecology, which enhanced the correlation between microbes and complex components formation during composting, especially in CM composting. Variance partitioning showed that both abiotic and biotic pathways were stimulated in conversion of HLS components after adding MnO 2 during CS composting, especially for the abiotic pathways. During CM composting, the MnO 2 promoted biotic effects on the conversion of HLS components. Above all, the addition of MnO 2 could stimulate pathways of biotic, abiotic or both of them to improve the humification degree of HLS by changing microbial ecology, which could be a promising way for promoting the application value of composting products.