[Study on three-dimensional fluorescence spectroscopy characteristics of humic acid during composting with microbes inoculation].

Composting is one of the municipal solid wastes (MSW) treatment ways. In order to increase composting humification process, in the present study, inoculation microbes were used in MSW composting. The experiment design included RUNck with no microbes inoculation and RUNmic with microbes inoculation. The inoculation microbes were composed of Bacillus casei, Lactobacillus buchneri, Candida rugopelliculosa and Trichoderma. During composting, samples were taken from MSW composting, and humic acid (HA) was extracted from composting and purified, the three-dimensional-excitation emission matrix fluorescence spectroscopy (3DEEM) characteristics and elemental analysis of the HA were determined, and the effect of inoculation microbes on the degree of humification of composting was studied. At initial stage of MSW composting, HA 3DEEM exhibited a peak of fulivc-like at an Ex/Em wavelength pair of 330/440 nm (peak a), and with MSW composting process, the excitation wavelength of peak a shifted from 330 to 350 nm. And a new peak of humic-like reformed nearby an Ex/Em wavelength pair of 390/470 nm (peak b). At 336 h of MSW composting, compared with RUNck (with no micromial inoculation), the fluorescence intensity of peak a (fulivc-like) nearby an Ex/Em wavelength pair of 350/440 in RUNmic (with microbial inoculation) was decreased, while that of peak b (humic-like) nearby an Ex/Em wavelength pair of 390/470 was slightly increased; the excitation and emission wavelength of peak a and peak b all shifted to long wavelengths. Elemental analysis indicated that C/H and O/C of HA molecule in RUNck increased by 9.68% and 10.91% respectively; and those of RUNmic increased by 11.11% and 20.37% at 336 h of MSW composting, respectively. The changes in HA 3DEEM and parameters of elemental analysis occurred in RUNmic at the final stage of composting, because degraded molecules, by the intense microbiological activity during composting, became reorganized to form more condensed compounds, richer in aromatic components. These results all led to the similar conclusion that inoculation microbes composting would accelerate the degree of HA humification, and increase the efficiency of composting.