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Refractory organic matter in different water matrices poses tremendous challenges for treatment processes. The substoichiometric titanium oxide (Ti 4 O 7) anode-designed reactive electrochemical membrane (REM) introduced for this critical problem and its performance was comprehensively evaluated in terms of current density, conductivity, membrane flux, total organic carbon (TOC) concentration, and pH using humic acid (HA) as a surrogate refractory organic compound. Increase in membrane flux from 500 to 2000 LMH showed a positive impact on the HA removal. The increase in current density and conductivity improved the mineralization performance. Depending on pH, the induction of electrical current to REM improved the HA removal from 0% to 80% compared to the case without power. It appeared that HA removal was achieved through direct electron transfer, oxidation by hydroxyl radicals (•OH), and electrosorption. The distribution of the three leading phenomena showed electrosorption as the main contributor to HA removal. The noticeable generation of •OH was recorded using electron paramagnetic resonance (EPR), and the structural transformation of HA was confirmed through the blue shift in the major fluorescence peak of HA. The energy consumption per g TOC was recorded to be economical for operation at lab-scale applications and thus highly promising for full-scale consideration. This study showed that REM could remove HA at a medium-level to a higher concentration with extraordinary stability. [Display omitted] • Ti 4 O 7 REM efficiently removed humic acid at mild conditions. • Membrane flux showed insignificant impact on the performance of REM. • A substantial blue shift was noted in fluorescence spectra of humic acid by REM. • Humic acid first transformed followed by adsorption on REM. • EPR provided evidence of hydroxyl radical by REM. [ABSTRACT FROM AUTHOR]

• REM effectively removed fluorescence components in secondary effluent. • REM system showed consistent performance in repeated experiments. • FT-ICR MS confirmed extensive degradation/transformation of DOM on REM surface. • Highly unsaturated and phenolic compounds were transformed to the aliphatic. • Sulfur-containing molecular formulas were easily degraded. This research evaluated the performance of reactive electrochemical ceramic membrane (REM) in treating secondary effluent and investigated the fate of dissolved organic matter (DOM) at the molecular level. The role of adsorption, electrosorption, and oxidation in DOM removal was comprehensively elucidated based on fluorescence spectroscopy and high-resolution mass spectrometry (FT-ICR MS). Among the fluorescence components (C1-C3) in secondary effluent, microbial humic-like C2 showed fewer adsorption on the REM surface without applying an electrical potential. The electrosorption helped an enhanced uptake of all DOM components and transformed them onto the electrode surface. The fluorescence components and all three fractions (hydrophilic, transphilic, and hydrophobic) were rapidly degraded, and finished water with stable DOM was obtained. The leading degradation phenomena were the change of the unsaturated compounds to the aliphatic and transformation of large-sized molecules to medium and small-sized ones. Above 70% of the compounds in the secondary effluent acted as precursors, which were mineralized/degraded and transformed products were found on the REM surface and in the finished water. The compounds containing sulfur (CHOS) were easily and preferably degraded/mineralized, followed by the compounds containing nitrogen (CHON) and CHO. The oxidation of DOM led to the extensive formation of organo-chlorinated compounds, which contributed above 80% in products. Overall, the combination of fluorescence spectroscopy and FT-ICR MS provided unique behavior of DOM in the secondary effluent toward electro-oxidation in the REM system. These findings could help explore the potential of REM for different water matrices to project the possible composition of DOM in the finished water. [Display omitted] [ABSTRACT FROM AUTHOR]

• Higher chlorine consumption was noted during wet season in drinking water networks. • NDMA and NDMA-FP were found to increase with increase in length of distribution. • Humic-like component in finished water acted as a surrogate of residual chlorine. • Fluorescence peaks, I 245/410 and I 335/410 , correlated with chlorine consumption. • Fluorescence-based monitoring could help in adjusting chlorine dosage. Several factors play a role in chlorine consumption in drinking water networks such as microbial contamination and dissolved organic matter (DOM). This study investigated the simultaneous impacts of seasonal variations on chlorine consumption and DOM composition for a year-long period in three different full-scale water distribution networks in a southern city of China. Efforts were made to determine the association between different fluorescence moieties in DOM of finished water and chlorine consumption through excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC). The chlorine consumption was also found to be directly related to N -Nitrosodimethylamine (NDMA) and NDMA-formation potential (NDMA-FP), presenting consequence of excess residual chlorine. The wet season with high rainfall showed elevated consumption of chlorine on the opposite of dry season. During wet season, humic-like component in finished water was dominant than protein-like features and its abundance decreased in dry season. Results proved that chlorine consumption was season dependent and highly influenced by DOM composition in the finished water. Unlike the bulk quality parameters and protein-like component, fluorescence moieties related to humic substances acted as a surrogate for the chlorine consumption. Based on humic-like component, a single excitation based fluorescence peak, I 245/410 or I 335/410 , was also extracted from EEMs of finished water samples and validated on different water distribution networks. These two single peaks well-explained the trends of residual chlorine and have the potential for on-line monitoring and portable purposes. This field-based study demonstrated application of fluorescence spectroscopy in designing chlorine dose to obtain optimal residual chlorine at consumer's tap. [ABSTRACT FROM AUTHOR]

N -nitrosamines have been identified as emerging contaminants with tremendous carcinogenic potential for human beings. This study examined the seasonal changes in the occurrence of N -nitrosamines and N -nitrosodimethylamine formation potential (NDMA-FP) in drinking water resources and potable water from 10 drinking water treatment plants in a southern city of China. The changes in N -nitrosamines are well correlated with dissolved organic matter (DOM), particularly fluorophores, which were measured and compared between traditional fluorescence indices and excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC). Four of N -nitrosamine species including N -nitrosodimethylamine (NDMA), N -Nitrosodibutylamine (NDBA), N -Nitrosopyrrolidine (NPYR), and N -Nitrosodiphenylamine (NDPhA) are found to be abundant compounds with an average of 29.5% (26.7%), 20.0% (25.2%), 18.9% (16.0%), and 9.0% (9.9%) in the source (and treated) water, respectively. The sum of N -nitrosamines concentration is recorded to be low in the wet season (July–September), whereas the dry season (October–December) provided opposite impacts. EEM-PARAFAC modeling indicated the predominance of humic-like component (C1) in the wet season while in the dry season the water was dominant in protein-like component (C2). All the N -nitrosamines excluding NDPhA and N -Nitrosomorpholine (NMOR) showed a strong association with protein-like component (C2). In contrast, humic-like C1, which was directly influenced by rainfall, was found to be a suitable proxy for NMOR and NDPhA. The results of this study are valuable to understand the correlation between different N -nitrosamines and DOM through adopting fluorescence signatures. Image 1 • The mean concentration of each N -nitrosamine in drinking water is below 5 ng/L. • Sum of N -nitrosamines in drinking water is higher in dry season than wet season. • Humic-like component shows higher intensity in wet season. • Most of N -nitrosamines associate with protein-like component. • Compare to HIX and BIX, EEM-PARAFAC provides better proxies for N -nitrosamines. [ABSTRACT FROM AUTHOR]

In biological wastewater treatment systems, extracellular polymeric substances (EPS) are continuously excreted as a response to environmental changes and substrate conditions. It could severely affect the treatment efficacy such as membrane fouling, dewaterability and the formation of carcinogenic disinfection by-products (DBPs). The heterogeneous dissolved organic matter (DOM) with varying size and chemical nature constitute a primary proportion of EPS. In the last few decades, fluorescence spectroscopy has received increasing attention for characterizing these organic substances due to the attractive features of this low-cost spectroscopic approach, including easy sample handling, rapid, non-destructive and highly sensitive nature. In this review, we summarize the application of fluorescence spectroscopy for characterizing EPS and provide the potential implications for online monitoring of water quality along with its limitations. We also link the dynamics of fluorescent dissolved organic matter (FDOM) in EPS with operational and environmental changes in wastewater treatment systems as well as their associations with metal binding, membrane fouling, adsorption, toxicity, and dewaterability. The multiple modes of exploration of fluorescence spectra, such as synchronous spectra with or without coupling with two-dimensional correlation spectroscopy (2D-COS), excitation-emission matrix (EEM) deconvoluted fluorescence regional integration (FRI), and parallel factor analysis (PARAFAC) are also discussed. The potential fluorescence indicators to depict the composition and bulk characteristics of EPS are also of interest. Further studies are highly recommended to expand the application of fluorescence spectroscopy paired with appropriate supplementary techniques to fully unravel the underlying mechanisms associated with EPS. Unlabelled Image • Fate of fluorescence moieties in EPS of WWTPs is elucidated. • Modes of fluorescence spectra: 2D-COS, EEM, and PARAFAC, are broadly discussed. • Membrane fouling and sludge properties are linked with the FDOM in EPS analyzed. • Intensity of protein– and humic–like fluorescence indicates sludge properties. • On-line fluorescence sensors are urgently needed for wide scale applications. [ABSTRACT FROM AUTHOR]