Analysis of the time series difference of the material structure evolution of DOM and humic acid during composting of different materials

Dissolved organic matter (DOM) and humic acid (HA) were extracted from three composting processes of chicken manure without bacterial agent (CM), chicken manure with bacterial agent (CMB) and kitchen waste (FW). The material structure and transformation time sequence of DOM and HA were characterized by fluorescence spectrum parallel factor analysis and two-dimensional correlation spectrum analysis. The results showed that the humification index (HIX) value of DOM was CMB>CM>FW, FW compost had stronger autogenous source characteristics of organic matter, and CMB compost had the highest degree of organic matter humification. Compared to composting time, the spectral structural characteristics of DOM and HA had a stronger response to the type of compost; the relative contents of protein-like components in DOM of the three composts were CM>FW>CMB, and humus components showed CMB>FW>CM; the relative content of protein-like components in HA was CM>CMB(FW), and humus-like components showed CMB(FW)>CM. The two-dimensional correlation spectra showed that the evolution sequence of DOM components in chicken manure compost was as follows: humic acid-like>tyrosine-like>tryptophan-like>fulvic acid-like. The components of HA were as follows: tyrosine-like>fulvic acid-like>tryptophan-like; the evolution sequence of DOM components in kitchen waste was as follows: tryptophan-like>tyrosine-like>fulvic acid-like; the components of HA were as follows: humic acid-like>tyrosine-like>tryptophan-like>fulvic acid-like. Appropriate moisture content was conducive to the generation of humic-like substances in DOM. The decrease of ammonia nitrogen (NH₄ ⁺-N) content was related to the degradation of protein-like substances and the enhancement of humic degree in DOM, and nitro-nitrogen (NO₃ ⁻-N) content was significantly positively correlated with humic-like components. A decrease in water-soluble organic carbon (DOC) and water content may signal increased HA humification during composting.