Identification of visible colored dissolved organic matter in biological and tertiary municipal effluents using multiple approaches including PARAFAC analysis

Min Yang , Ashraful Islam , Guangxi Sun , Ayman N. Saber , Wei Shang , Xingcan Zheng , Yu Zhang


Received November 17, 2021,Revised , Accepted January 29, 2022, Available online February 08, 2022

Volume 34,2022,Pages 174-183

This study provided insights into the persistent yellowish color in biological and tertiary effluents of municipal wastewater through a multi-characterization approach and fluorescence excitation-emission matrix-parallel factor (EEM-PARAFAC) analysis. The characterization was performed on three to five full-scale municipal wastewater treatment plants (WWTPs), including differential log-transformed absorbance (DLnA) spectroscopy, resin fractionation, size-exclusion chromatography for apparent molecular weight analysis (SEC-AMW), and X-ray photoelectron spectroscopy (XPS) analysis. Hydrophobic acids (HPOA) were abundant in visible colored dissolved organic matter (DOM). The SEC-AMW result showed that the molecular weight of the colored substances in the secondary effluents is mainly distributed in the range of 2–3 kDa. Through XPS analysis, C-O/C-N and pyrrolic/pyridonic (N-5) were found to be positively correlated with chroma. PARAFAC component models were built on biological (two components) and tertiary effluent (three components) and the correlation analysis revealed that PARAFAC component 2 in biological effluent (BE-C2) and component 1 in tertiary effluent (TE-C1), which were ascribed to Hydrophobic acids and Humic acid-like, were the responsible visible colored DOM components cause yellowish color. In addition, component similarity testing found that the identified visible colored DOM PARAFAC BE-C2, and PARAFAC TE-C1 were identical (0.96) in physicochemical properties, with 4% removal efficacy on average, compared with 11% for invisible colored DOM. This implied that tertiary effluents containing colorants (TE-C1) were resistant to degradation/removal using different disinfection and filtration processes in advanced treatments. This sheds light on many physicochemical aspects of PARAFAC-identified visible colored DOM components and provides spectral data to build an online monitoring system.

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