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Characteristic Regions of the Fluorescence Excitation–Emission Matrix (EEM) To Identify Hydrophobic/Hydrophilic Contents of Organic Matter in Membrane Bioreactors

Xiao, Kang, Shen, Yuexiao, Liang, Shuai, Tan, Jihua, Wang, Xiaomao, Liang, Peng, Huang, Xia
Environmental science & technology 2018 v.52 no.19 pp. 11251-11258
Monte Carlo method, acids, chemical bases, dissolved organic matter, fluorescence, fluorescent dyes, hydrophilicity, hydrophobicity, membrane bioreactors, monitoring, regression analysis, wastewater treatment, wavelengths
This study systematically investigated the correlations between fluorescence distributions characterized by the excitation–emission matrix (EEM) and hydrophobic/hydrophilic composition of dissolved organic matter (DOM) in membrane bioreactors (MBRs). On the basis of samples from 10 full-scale MBRs, we performed point-to-point comparisons among different components using an EEM fluorescence quotient (FQ) method and obtained a hydrophobic/hydrophilic fluorophore distribution map via Wilcoxon signed rank test. Hydrophobic acids/bases (HOA/HOB) concentrated in the low-wavelength region [excitation wavelength (Ex) < 235 nm], while hydrophilic substances (HIS) were enriched in the region of Ex > 235 nm [especially with emission wavelength (Em) = 300–360 nm]. Quantitatively, EEM regional contribution to whole wavelength fluorescence was found to significantly correlate with the hydrophobic/hydrophilic proportions of DOM, with Pearson’s coefficients of 0.94 and 0.78 (p < 0.01) for HOA and HIS, respectively. We established a linear regression model showing the HOA proportion as a function of the EEM regional contribution at (Ex, Em) = (200–285, 340–465 nm), with R² = 0.876, which was validated via leave-one-out cross-validation and Monte Carlo simulation. This study shows a statistically hydrophobicity-dependent fluorescence property across different MBRs, and it might be applied to provide a quick estimation of hydrophobic/hydrophilic composition of DOM in wastewater treatment systems based on EEM monitoring.