[Spectroscopic Characterization of DOM During Hyperthermophilic Composting of Sewage Sludge]

Spectroscopy methods such as three-dimensional excitation-emission (3D-EEM) fluorescence spectroscopy were applied to analyze the structures and changes of DOM in hyperthermophilic composting of sewage sludge to fully understand the advantages of hyperthermophilic composting in promoting sludge maturity. The results showed that the temperature reached its peak value at 90℃ and remained over 80℃ for 5 d. The thermophilic period more than 50℃ lasted for 22 d. This indicated that the microorganisms were metabolically active during the composting. The parameters of UV-visible (UV-Vis), including E₂₅₃/E₂₀₃, SUVA₂₈₀, and S_275-295, significantly changed from days 0 to 23, showing that the aromaticity degree of DOM and the humification degree of the compost gradually strengthened. Combined with the fluorescence regional integration (FRI), the 3D-EEM analysis results illuminated that the protein-like materials in DOM were completely degraded during days 0 to 6 of the hyperthermophilic composting and a large amount of humic acid-like and fulvic-like materials formed from days 0 to 23, indicating the compost was mature at the hyperthermophilic stage. This was consistent with the germination index (GI) on day 23 (GI=98.5%) as well. Based on the correlation analysis between spectroscopic parameters, P_Ⅴ,/P_Ⅲ, showed close relationship with others (r ≥ 0.68), showing their potential as indicators for maturity of hyperthermophilic composting. The results above confirmed that fermentation time could be greatly shortened to about 20 d by using the hyperthermophilic composting, which has great potential for application in organic solid waste management.