Fast Tracking and Detection of Organic Matter in an Urban Sewage Treatment Plant Using Fluorescence Spectroscopy and UV-Vis Absorption Spectroscopy

Organic matter distributions and concentrations at various stages of an urban wastewater treatment plant were analyzed via ultraviolet‒visible (UV‒Vis) absorption and three-dimensional fluorescence spectroscopy. Six components identified via the excitation‒emission matrix and PARAFAC analysis revealed that components related to tryptophan (components 1, 3, and 6) correlated strongly with the chemical oxygen demand (COD) concentration, with Pearson correlation coefficients of 0.656, 0.447, and 0.674 respectively. Analysis of the fluorescence and UV‒Vis absorption parameters revealed a reduction in the organic matter content, increased humification, and a shift from exogenous organic substances to endogenous organic substances throughout the sewage treatment process. Notably, the humification index had the highest correlation with the COD level (–0.834). Based on the use of Monte Carlo–uninformative variable elimination‒partial least squares for characteristic wavelength extraction from normalized fluorescence and absorption spectra, a COD characteristic fusion spectral analysis model was developed. The results revealed good agreement between the COD concentrations obtained via feature fusion spectral analysis and the true COD values obtained via the potassium dichromate method. The coefficient of determination between the predicted COD values and the true COD values in the testing set reached 0.9725, the root mean square error was only 10.51 mg/L, and the residual predictive deviation was 4.74. These findings suggest the efficacy of using UV‒Vis absorption and three-dimensional fluorescence spectroscopy for direct COD tracking and detection in wastewater treatment processes without any pretreatment.

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