Effect of inoculating microbes in municipal solid waste composting on characteristics of humic acid

Municipal solid waste (MSW) compost contains a significant amount of humic substances. In this study, the compost consisted of residual MSW with the metal, plastic and glass removed. In order to enhance degradation processes and the degree of composting humification, complex microorganisms (Bacillus casei, Lactobacillus buchneri and Candida rugopelliculosa) and ligno-cellulolytic (Trichoderma and White-rot fungi) microorganisms were respectively inoculated in the composting process. During the MSW composting, humic acid (HA) was extracted and purified. Elements (C, N, H, O) and spectroscopic characteristics of the HA were determined using elementary analyzer, UV, Fourier transform infrared (FTIR), and fluorescence spectroscopy. The elements analysis, UV, FTIR and fluorescence spectra all led to the same conclusion, that is inoculations with microbes led to a greater degree of aromatization of HA than in the control process (CK) with no inoculation microbes. This indicated that inoculation with microbes in composting would improve the degree humification and maturation processes, in the following order: lingo-cellulolytic > complex microorganisms > CK. And mixed inoculation of MSW with complex microorganisms and lingo-cellulolytic during composting gave a greater degree of HA aromatization than inoculation with complex microorganisms or lingo-cellulolytic alone. But comparing with the HA of soil, the HA of MSW compost revealed a lower degree of aromatization.