Characterization of dissolved organic matter in urban sewage using excitation emission matrix fluorescence spectroscopy and parallel factor analysis

Wastewater dissolved organic matter (DOM) from different processing stages of a sewage treatment plant in Xiamen was characterized using fluorescence and absorption spectroscopy. Parallel factor analysis modeling of excitation-emission matrix spectra revealed five fluorescent components occurring in sewage DOM: one protein-like (C1), three humic-like (C2, C4 and C5) and one xenobiotic-like (C3) components. During the aerated grit chamber and primary sedimentation tank stage, there was only a slight decrease in fluorescence intensity and the absorption coefficient at 350 nm (a350). During the second aeration stage, high concentration of protein-like and short-wavelength-excited humic-like components were significantly degraded accompanied by significant loss of DOC (80%) and a350 (30%), indicating that C1 and C2 were the dominant constituents of sewage DOM. As a result, long-wavelength-excited C4 and C5 became the dominant humic-like components and the DOM molecular size inferred from the variation of spectral slope S (300-650 nm) and specific absorption (a280/DOC) increased. Combination use of Fmax of C1 and the ratio of C1/C5, or a350 may provide a quantitative indication for the relative amount of raw or treated sewage in aquatic environment.