Chemodiversity of Fulvic Acid as Affected by Different Biowastes Materials During Composting: An Analysis by Ultraviolet–Visible Spectroscopy

To explore the effect of UV–Vis spectra of different compost materials, this paper adopted nine other research materials on spectral characteristics of composting fulvic acid (FA). The results showed that the UV–Vis unit molar absorption strength increased in each compost, particularly stem waste, leaf waste, and cabbage waste, implying that the aromatization and unsaturated degree of FA increased, as did the humification of compost. Correlation analysis showed that germination index (GI) was positively correlated with E250/E365, significantly positively correlated with SUVA254 and S275–295, SR, and strongly negatively correlated with E253/E203, respectively. Therefore, E253/E203, SUVA254, S275–295, and E250/E365 could be used to evaluate compost maturity. Furthermore, all compost could be regarded as an indicator of reaching maturation when SUVA254 is higher than 0.21 mg/L. The change of maturity parameters indicated that E465/E665 of leaf waste, cabbage waste, stem waste, and municipal solid waste declined during composting, SUVA254, A240–400, S275–295, A3/A2 of kitchen waste, chicken manure, pig manure, and peat increased during composting. To summarize, the organic matter molecular weight, compost stability, and degree of humification significantly increased. Compost was classified into three groups based on hierarchical cluster analysis: cabbage waste, stem waste, and peat were in the first group; kitchen waste and leaf waste were in the second group; and pig manure, chicken manure, municipal solid waste, and grass waste were in the third group.