Study on dynamic spectral characteristics of humic acid in municipal solid wastes composting

In the present study, the compost consisted of residual MSW with metal, plastic and glass removed. The composting process was assisted using industrial technology. During the composting, humic acid (HA) was extracted and purified. The spectroscopic characteristics of the HA were determined by using UV, FTIR, and fluorescence spectroscopy. During the composting process, the HA fluorescence spectra exhibited a sharp reduction in relative fluorescence intensity at the short wavelength region, and the primary peak shifted from 335 nm at the initial stage to 458 run at the final stage of composting, thereby approaching the main peak at 460-480 nm for HA in soil. The FTIR spectra exhibited a reduction in polysaccharides and aliphatic components, and a relative increase in aromatic components; while the HA UV spectra revealed an increase in conjugation and the degree of humification. However, compared with the E-4/E-6 value and the spectroscopic characteristics of HA in soil, the HA in the MSW compost has a relatively low molecular weight, a simpler structure and a relatively low degree of aromatic condensation, which also implies that the HA in compost is highly active.