Fluorescence Excitation Emission Matrix-parallel Factor Research Articles

Tracking the transformation of extracellular polymeric substances during the ultraviolet/peracetic acid disinfection process: Emphasizing on molecular-level analysis and overlooked mechanisms

In this study, the transformation mechanisms of extracellular polymeric substances (EPS) during ultraviolet/peracetic acid (UV/PAA) disinfection were elucidated based on multiple molecular-level analyses. After UV/PAA disinfection, the contents of soluble EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were reduced by 70.47 %, 57.05 % and 47.46 %, respectively. Fluorescence excitation-emission matrix-parallel factor and Fourier transform ion cyclotron resonance mass spectrometry analyses showed that during UV/PAA disinfection, EPS was transformed from the state characterized by high aromaticity, low saturation and low oxidation to the one with reduced aromaticity, increased saturation and higher oxidation. Specifically, sulfur-containing molecules (CHOS, CHONS, etc.) in EPS were converted into highly saturated and oxidized species (such as CHO), with the aromaticity index (AImod) decreasing by up to 53.84 %. Molecular characteristics analyses further indicated that saturation degree, oxidation state of carbon and molecular weight exhibited the most significant changes in S-EPS, LB-EPS and TB-EPS, respectively. Additionally, mechanistic analysis revealed that oxygen addition reaction was the predominant reaction for S-EPS (+O) and TB-EPS (+3O) (accounting for 31.78 % and 36.47 %, respectively), while the dealkylation was the main reaction for LB-EPS (29.73 %). The results were consistent with functional groups sequential responses analyzed by Fourier transform infrared and two-dimensional correlation spectroscopy, and were further verified by density functional theory calculations. Most reactions were thermodynamically feasible, with reaction sites predominantly located at functional groups such as CO, CO, CN and aromatic rings. Moreover, metabolomics analysis suggested that changes in metabolites in raw secondary effluent during UV/PAA disinfection were strongly correlated with EPS transformation. Our study not only provides a strong basis for understanding EPS transformation during UV/PAA disinfection at molecular-level but also offers valuable insights for the application this promising disinfection process.

Effect of rainfall-derived inflow and infiltration on dissolved organic matter in urban sanitary sewers using chemometric and machine learning approaches

This study investigated changes in dissolved organic matter (DOM) properties within urban sanitary sewers influenced by groundwater infiltration and excessive rainfall-derived inflow and infiltration (RDII). It employed optical indices and fluorescence excitation-emission matrix-parallel factor analysis (PARAFAC) coupled with self-organizing map (SOM) to compare DOM characteristics during wet weather flows (WWFs) and dry-weather flows (DWFs). Sampling sites impacted by RDII were identified based on flowrate. Optical indices and PARAFAC components (C1–C4) were used to differentiate DOM properties between DWFs and WWFs. In WWFs, E<sub>2</sub>/E<sub>3</sub> and S<sub>350-400</sub> increased, while spectral ratio (S<sub>R</sub>) decreased, indicating a shift towards smaller organic matters. Reduced fluorescence and humidification indices suggested the input of fresher/terrestrial organic matters. C3 and C4 exhibited significant distinctions, showing increased C3 and decreased C4 levels. The PARAFAC-SOM modeling further illustrated that water samples in the urban sewer system could be categorized based on the dominance of DOM properties. Principal component analysis revealed separation between DWF and WWF samples in principal component 1 (PC1), associated with molecular size. PC2 was linked to microbial activity in WWFs. Notably, DWF samples from the NY-11 site shifted to the positive side of the PC1 axis, while their corresponding WWF samples moved to the negative side.

Spatial distribution of sediment dissolved organic matter in oligotrophic lakes and its binding characteristics with Pb(II) and Cu(II).

Dissolved organic matter (DOM), the most active component in interstitial waters, determines the stability of heavy metals and secondary release in sediments. However, little is known about the composition and metal-binding patterns of DOM in interstitial water from oligotrophic lakes affected by different anthropogenic perturbations. Here, 18 interstitial water samples were prepared from sediments in agricultural, residential, tourist, and forest regions in an oligotrophic lake (Shengzhong Lake in Sichuan Province, China) watershed. Interstitial water quality and DOM composition, properties, and Cu(II)- and Pb(II)-binding characteristics were measured via physicochemical analysis, UV-vis spectroscopic, fluorescence excitation-emission matrix-parallel factor analysis (EEM-PARAFAC), and fluorescence titration methods. The DOM, which was produced mainly by microbial activities, had low molecular weights, humification degrees, and aromaticity. Based on EEM-PARAFAC results, the DOM was generally composed of tryptophan- (57.7%), terrestrial humic- (18.7%), microbial humic- (15.6%), and tyrosine-like (8.0%) substances. The DOM in the metal complexes was primarily composed of tryptophan-like substances, which accounted for ~42.6% of the DOM-Cu(II) complexes and ~72.0% of the DOM-Pb(II) complexes; however, microbial humic-like substances primarily contributed to the stability of DOM-Cu(II) (logKCu = 3.7-4.6) and DOM-Pb(II) (logKPb = 4.3-4.8). Water quality parameters did not significantly affect the stability of DOM-metal complexes. We demonstrated that the metal-binding patterns of DOM in interstitial water from oligotrophic lakes are highly dependent on microbial DOM composition and are affected by anthropogenic perturbations to a lesser extent.

Differences in dissolved organic matter (DOM) composition of soils from native eucalypt forests and exotic pine plantations impacted by wildfire in Southwest Australia

In recent decades, plantations of exotic species have transformed large tracts of forested landscapes, where they often form a mosaic with the surrounding native forest. Wildfires have also increased in frequency and intensity globally, impacting both plantation and native forests and affecting soil organic matter (SOM), including dissolved organic matter (DOM). DOM of soils is considered highly labile and likely sensitive to effects of fire and changes in land use. However, it is unclear how wildfire influences key characteristics of DOM in exotic plantations compared to native forest. In this study, we investigated the impacts of wildfire on chemical properties of DOM in exotic Pinus radiata plantations and adjacent native jarrah (Eucalyptus marginata) forest in southwest Australia. We coupled fluorescence excitation-emission matrix parallel factor analysis (EEM-PARAFAC) and 1H‐NMR with soil nutrient analyses to characterise soil DOM (0–5 cm) from burned and unburned plots of each forest type, four months after the fire. Four fluorescent components (humic-, fulvic-, microbial and protein-like substances) were derived from soil DOM using the PARAFAC model. DOM from burnt forest soils was predominantly of lower molecular weight (E2:E3) and contained a greater microbial-derived component and a lower fulvic component than unburnt forest. As expected, soil pH and labile inorganic P increased in both forest types after fire. By contrast, an increase in the amount of DOC after fire was only recorded in native forest, while δ15N signatures were more enriched in pine plantation soils after fire but not in native forest soils. Differences in impacts of fire on DOC and δ15N between forest types suggest a different response to fire according forest type, even though these differences were not evident above ground. The 1H NMR spectra of DOM revealed all samples were largely dominated by aliphatic structures. However, there were no significant differences in the overall spectra between forest types or between burnt and unburnt forests. Overall, our findings suggest that transformations in soil DOM after fire were affected by feedbacks between forest type and fire (where soils from pine plantations appeared to be more affected by fire).

Effects of organic additives on spectroscopic and molecular-level features of photo-induced dissolved organic matter from microplastics

The environmental occurrence and impact of dissolved organic matter leached from microplastics (MP-DOM) has been the subject of increased research interest. Commercial plastics, which typically contain additives, are subject to natural weathering processes and can eventually lose their additives. However, the effects of organic additives in commercial microplastics (MPs) on the release of MP-DOM under UV irradiation remain poorly understood. In this study, four polymer MPs (polyethylene; PE, polypropylene; PP, polystyrene; PS, polyvinylchloride; PVC) and four commercial MPs, including a PE zip bag, a PP facial mask, a PVC sheet, Styrofoam, were subjected to leaching under UV irradiation, and the MP-DOM was characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and fluorescence excitation emission matrix-parallel factor analysis (EEM-PARAFAC). Although UV light promoted the leaching of MP-DOM from both MP groups, the amount released was more pronounced for the polymer MPs than for the commercial MPs. The commercial MP-DOM was characterized by a prominent protein/phenol-like component (C1), while a humic-like component (C2) prevailed in the polymer MPs. FT-ICR-MS identified a higher number of unique molecular formulas for the commercial than for the polymer MP-DOM. The unique molecular formulas of commercial MP-DOM included known organic additives and other breakdown products, while the polymer MP-DOM featured more pronounced unsaturated carbon structures in its identified unique formulas. Several molecular-level parameters showed significant correlations with fluorescence properties, such as CHO formulas (%) with C1 and condensed aromatic structure (CAS-like, %) with C2, suggesting the potential application of fluorescent components as an optical descriptor for the complex molecular-level composition. This study also revealed the possible high environmental reactivity of both polymer MPs and fully weathered plastics due to the unsaturated structures generated in sunlit environments.

Release of adsorbed copper and carbon during Fe(Ⅱ) catalytic conversion of ferrihydrite-humic acid coprecipitation under acidic condition: Mechanism and properties

The mobility of copper (Cu) may be significantly impacted during the conversion of ferrihydrite-humic acid (Fh-HA) coprecipitates. However, the environmental behavior of the adsorbed Cu in Fh-HA coprecipitation and the kinetic process of organic carbon (C) during the Fe(Ⅱ)-catalyzed Fh-HA coprecipitates conversion remains unclear. In this study, a series of Fh-HA coprecipitates with various C/Fe molar ratios were synthesized. Furthermore, the effects of the Fe(Ⅱ) mediated Fh and Fh-HA conversion processes on Cu mobility and carbon release characteristics under acidic condition were investigated. The results show that the specific surface area of Fh-HA is reduced as compared to pure Fh, which impedes the conversion of Fe minerals and increases the release of Cu to the solution. The rate of conversion can be accelerated by increasing the Fe(II) concentration, resulting in the retention of Cu in the mineral structure. As compared to artificial HA, Elliott soil humic acid (ESHA) coprecipitated with Fh resulted in a reduced Cu release. According to results of the fluorescence excitation emission matrix-parallel factor analysis, the "release-resorption" process of carbon occurred during conversion and low molecular weight HA related to the biological activity was the main source of the released organic carbon. The major functional groups were C-O functional groups and phenolic hydroxyl groups, and Cu was involved in the formation of Fe-O-Cu after conversion. The findings of this study provide crucial information for comprehending the biogeochemical process of Cu associated with Fh and Fh-HA coprecipitates.

Spectral characteristics coupled with self-organizing maps analysis on different molecular size-fractionated water-soluble organic carbon from biochar.

Biochar-derived water-soluble organic carbon (BWSOC) plays important roles in the environmental effect of biochar. The environmental behavior and fate of BWSOC are closely related to its size distribution and chemical components. However, the molecular size-dependent BWSOC components and properties remain little known. To evaluate molecular size-dependent BWSOC characteristics, BWSOC samples were prepared by pyrolyzing biomasses in air-limitation and N2-flow atmospheres at 300-600 °C and fractionated through a series of membranes with different pore sizes including 0.7 μm, 0.45 μm, 100 kDa, 10 kDa, 3 kDa, and 1 kDa. In all BWSOCs, <1 kDa and 0.45-0.7 μm fractions had the maximum abundance (mean: 40.6 %) and the minimum abundance (mean: 4.4 %), respectively. The spectral characteristics of BWSOC including polarity index, spectral slope, and humification index varied significantly with molecular size. The fluorescence excitation-emission matrix parallel factor (EEM-PARAFAC) analysis indicated that BWSOC was mainly composed of three organic components (humic-like, fulvic-like, and aromatic protein/polyphenol-like substances). Humic-like and fulvic-like substances mainly existed in <1 kDa fraction, while aromatic protein/polyphenol-like substances mainly existed in medium-size fractions (3 kDa-0.45 μm). The different locations of <1 kDa, 1 kDa-0.45 μm, and 0.45-0.7 μm fractions in EEM and PARAFAC self-organizing maps indicated self-organizing maps could effectively distinguish 0.45-0.7 μm, 1 kDa-0.45 μm, and < 1 kDa fractions via the variations of fluorescence intensity and organic components. Additionally, the distribution ratio of different molecular size fractions as well as the abundances of organic components in different molecular size fractions were strongly controlled by pyrolysis atmospheres (air-limitation and N2-flow). This study systematically clarified the organic components and properties of different molecular size fractions in BWSOC, and the results are helpful to understand the possible environmental behavior and fate of BWSOC.

Variations in the concentration, composition, and sources of WEOM in erosion and deposition landscapes over an erosion intensity gradient on the Loess Plateau of China

Water-extractable organic matter (WEOM) is the most active and mobile fraction of soil organic matter and responds sensitively to soil erosion. However, previous studies on the chemical nature of WEOM in the erosion and deposition landscapes were controversial at site-level studies and mainly focused on surface soils, limiting our assessment of WEOM’s environmental fate at larger and deeper scales. Here, we collected eroded soils and deposited sediments from a depth of 0–200 cm in five eroding catchments with an erosion intensity gradient across the Loess Plateau. We examined the concentration, composition, and potential sources of WEOM using UV–visible absorption and fluorescence excitation-emission matrix-parallel factor analysis. Soil WEOM quantity and quality varied significantly in the erosion and deposition landscapes, with greater variations in soils below 20 cm, where WEOM in the deposition zone was characterized by higher concentration, aromaticity, hydrophobicity, and UVA and UVC humic-like components derived from terrestrial and soil organic matter. WEOM variations in deep soils increased with increasing erosion modulus among sites, and were mainly driven by changes in soil organic carbon concentration, aggregate stability, and carbon to nitrogen ratio. However, the pattern of WEOM parameters between erosion and deposition zones at 0–20 cm was opposite to that in soils below 20 cm. Vegetation inputs compensated the loss of organic matter in sites with suitable climatic status and weak erosion, and led to higher concentrations and exogenous features of WEOM in the surface erosion area. Concludingly, the WEOM concentration, components, and sources differed significantly between erosion and deposition zones, and these differences, as well as their response to erosion intensity, revealed an opposing pattern in surface and deep soils.

Emerging applications of EEM-PARAFAC for water treatment: a concise review

In this work, the application of EEM-PARAFAC (fluorescence excitation-emission matrix-parallel factor analysis) in water treatment processes, has been summarized. First, its most common use, the characterization and monitoring of dissolved organic matter (DOM) along freshwater ecosystems, drinking and wastewater treatment plants (DWTP and WWTP, respectively), was reviewed. In particular for DWWT/WWTP, the effect towards the different DOM fractions after adsorption, coagulation, biological/chemical processes or tertiary treatments (e.g. advanced oxidation processes), as well as the PARAFAC components scores (i.e. fluorescence intensity) correlation with disinfection by-products formation, were reported. On the other hand, barely barely for the first time, we also reviewed the emerging uses of EEM-PARAFAC focused on water treatment studies, such as, the simultaneous analysis of several fluorescent CECs degradation (with the concomitant formation of major by-products), the use of PARAFAC components scores decay to estimate certain CECs removals, the correlation of reactive oxygen species formation with the specific DOM fractions originating them, or even the study of interactions between DOM with other water constituents. Therefore, this study aims to extend the uses of this economical, reagentless and low time-consuming tool to obtain further insight into fluorescent compounds during water treatment processes, mainly to: i) tentatively elucidate structural modifications of target analyte (DOM or CECs), ii) obtain semi-quantitative data on parent pollutants and by-products variation, and iii) investigate the plausible mechanistic aspects which are involved.

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

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.

Insight into interactions of heavy metals with livestock manure compost-derived dissolved organic matter using EEM-PARAFAC and 2D-FTIR-COS analyses

Dissolved organic matter (DOM), as the most active ingredient in compost, directly determines the speciation and environmental behavior of HMs. Here, the binding properties of DOM derived from chicken-manure compost (CHM), cow-manure compost (COM) and pig-manure compost (PIM) with HMs were explored by analyses of Fluorescence excitation-emission matrix parallel factor (EEM-PARAFAC) and two-dimensional correlation Fourier transform infrared spectroscopy (2D-FTIR-COS). Results showed that the binding characteristics vary with origin of DOM and type of HMs. The fulvic-like component dominated the transformation of HMs speciation, and CHM-DOM had higher affinity with HMs and greater risk causing pollution due to its higher aromaticity, molecular weight and distribution of fluorescent components. Moreover, Cu(II) can efficiently bind to DOM with the stability constants (log kM) ranging from 4.53 to 5.38, followed by Pb(II) (3.34–3.57), whereas Cd(II) can hardly bind to DOM. The amide and polysaccharide were the predominant sites for HMs binding in CHM-DOM, and polysaccharide and phenolic in COM-DOM, while phenolic and amide in PIM-DOM, respectively. Although the proportion of protein-like components and non-fluorescent polysaccharides in DOM were low, their role in HMs binding should not be ignored. In brief, the environmental risk caused by livestock manure compost may originate from interactions between DOM and HMs.

EEM–PARAFAC characterization of dissolved organic matter and its relationship with disinfection by-products formation potential in drinking water sources of northeastern China

Dissolved organic matter (DOM) is the precursor of disinfection by-products (DBPs) which is widely found in the aquatic environment. The analysis of DOM in raw water is helpful to evaluate the formation potentials of DBPs. However, there is relatively little research on the DOM identification of raw water in northern China. In this study, the variation in DOM in M reservoir water in one year by fluorescence excitation–emission matrix-parallel factor analysis (EEM–PARAFAC) was investigated to evaluate the DBP formation potential (DBPFP). The results suggested that five components, namely, two humic-like substances (C2, C3), two fulvic-like substances (C1, C4) and one protein-like substance (C5), were identified in the DOM of M reservoir water. The content of DOM in autumn and winter was higher than that in spring and summer. The source of DOM in the water body of M reservoir was mainly from terrestrial source, but less from aquatic source. The source, types and humification degree of DOM affect the formation of DBPs. The formation potential of DBPs had the following order: trihalomethanes (THMs) > dichloroacetic acid (TCAA) > trichloroacetic acid (DCAA) > chloral hydrate (CH). The formation potentials of THM and TCAA were strongly correlated with C2 (rTHM = 0.805, rTCAA = 0.857). The formation potential of CH has a good correlation with C1 (r = 0.722). The formation of DCAA has a good correlation with C4 (r = 0.787). DOM and DBPFP were negatively correlated with the biological index (BIX) and fluorescence index (FI) of the raw water, and positively correlated with the humification index (HIX).

Characterizing fluorescence fingerprints of different types of metal plating wastewater by fluorescence excitation-emission matrix

To prevent the illegal discharge of metal plating wastewater (MPW), it is necessary to explore a monitoring method that could achieve the identification of MPW in natural water bodies. Fluorescence excitation-emission matrix-parallel factor (EEM-PARAFAC) analysis might be a promising tool for the detection of MPW. However, before conducting the practical monitoring, the apparent fluorescence features of different kinds of MPW must be first understood. In this study, six types of MPW (576 samples) from ten metal plating plants were collected and their fluorescence fingerprints (FFs) were characterized by EEM-PARAFAC analysis. Results showed that pretreatment wastewater (PTW), copper-contained electroplating wastewater (Cu-EPW), nickel-contained electroplating wastewater (Ni-EPW), copper-contained electroless wastewater (Cu-ELW), nickel-contained electroless wastewater (Ni-ELW), and metal plating effluent (MPE) presented one, three, one, one, two, and three types of FFs, respectively. Among them, three individual fluorescent components were identified in Ni-EPW and two were decomposed in other kinds of MPW. Owing to the discrepancies of production processes, electroplating additives, wastewater treatment techniques, and management levels, different metal plating plants owned different FFs. By spectral comparison, the tyrosine-like components in PTW and Ni-ELW might derived from some phenolic and benzenesulfonic acidic compounds. Fluorescent component similarity analysis indicated that EEM-PARAFAC technique could distinguish the raw and treated MPW. This study not only constructed the first FF database for MPW, but also provided valuable guidance for their practical monitoring in aquatic environment.

High cadmium pollution from sediments in a eutrophic lake caused by dissolved organic matter complexation and reduction of manganese oxide

Eutrophication and metal pollution are global environmental problems. The risk of metal pollution is high in the eutrophic lakes because of high mobility of metal in sediments. However, the mechanism of cadmium (Cd) mobility in sediments is still unclear. Here we study the mobilization of Cd in sediments from the eutrophic Lake Taihu via monthly field monitoring of mobile Cd using diffusive gradient in thin films (DGT) and high resolution dialysis (HR-Peeper) techniques. We found a high mobility of Cd in sediments in February and March, resulting from reductive dissolution of Mn oxide mediation by high microbial activities, as shown by the similarities in distribution patterns of DGT-labile Cd and Mn. A two orders of magnitude increase in dissolved Cd concentrations (about 28 μg L−1) was observed in May and June, with dissolved Cd concentrations in overlying water about 110 times higher than the criteria continuous concentration set by Environmental Protection Agency. Hourly changes were found to coincide and correlate between dissolved Cd and dissolved organic matter (DOM) under simulated anaerobic conditions, strongly suggesting that the sudden outbreak of Cd pollution observed in the field resulted from the complexation of DOM with Cd in sediments. This was further supported by the NICA-Donnan model that more than 71% of dissolved Cd in the pore water in May and June was present as Cd-DOM complexes. Three components of DOM including humic-, tryptophan-, and tyrosine-like components in the sediments in June was identified using the fluorescence excitation emission matrix-parallel factor analysis. We found that Cd was stable complexed with tyrosine-like component. The Fourier transform infrared and two-dimensional correlation spectroscopy further revealed that Cd was bound to phenolic OH, alkene CC, alcoholic CO, aromatic CH, and alkene CH groups. Our study effectively promotes the understanding of Cd mobilization in sediments and highlights the risk of sudden Cd pollution events in the eutrophic lakes.

Mixing behavior, biological and photolytic degradation of dissolved organic matter in the East China Sea and the Yellow Sea

Optical properties of dissolved organic matter (DOM) were used as an indicator of the quantitative and qualitative changes occurring in marine DOM. The spatiotemporal distribution, bioavailability, and photoreactivity of chromophoric DOM (CDOM) and dissolved organic carbon (DOC) were investigated in the East China Sea (ECS) and the Yellow Sea (YS) during spring and summer using absorption spectroscopy and fluorescence excitation-emission matrix–parallel factor analysis. Over a 4-month laboratory study, we measured changes in six commonly used optical indices, including spectral slope (S275–295), slope ratio (SR: S275–295/S350–400), specific ultraviolet absorbance (SUVA254), ratio of the sum of protein-like components to the sum of humic-like components (Cprotein/Chumic), biological index (BIX), and humification index (HIX) to determine their changes following biological and photochemical degradation processes. Significant seasonal variations were observed in the spectral characteristics of CDOM in the ECS and the YS, indicating a stronger influence of the terrestrial origin and highly aromatic content of DOM in summer than in spring; this result was likely the consequence of an increase in the Changjiang River discharge, phytoplankton production, and biological activity, resulting in an increase in DOM production. Significant correlation between salinity and optical parameters (SUVA254, S275–295, S350–400, Cprotein/Chumic) indicated that water mixing strongly influenced the distributions of these optical parameters. The bioreactivity and photoreactivity of DOM varied depending on the source material, and the autochthonous protein-like DOM was more prone to biodegradation than the terrestrial DOM. The photodegradation processes acted preferentially on the CDOM than the colorless DOM. These results demonstrated that the optical parameters exhibited distinct changes during the mixing and the biodegradation and photodegradation processes and explained the seasonal distribution of DOM in the ECS and the YS.

Effect of sulfonamides on the dissolved organic matter fluorescence in biogas slurry during anaerobic fermentation according to the PARAFAC analysis

The biogas slurry produced by anaerobic fermentation process contained a large amount of dissolved organic matter (DOM). In this study, the reason for the effect of sulfanilamide antibiotics (SAs) on DOM components was revealed by analyzing the interaction between microbial community structure and DOM composition in the biogas slurry. Four components of DOM, including tyrosine-like, tryptophan-like or xenobiotic-like, Ultraviolet A (UVA) humic-like and UVA marine humic-like substances, were identified from all the samples through fluorescence excitation emission matrix-parallel factor (EEM-PARAFAC) analysis. The most abundant phyla in biogas slurry were identified to be Firmicutes (60.99 %), Bacteroidetes (19.65 %), Proteobacteria (15.33 %) and Actinobacteria (3.15 %). The contents of soluble microbial byproduct-like substances were related to the growth and metabolism of high abundance of bacterial phyla. Firmicutes could lead to the content change of tyrosine-like substance. The content of the xenobiotic-like substance was negatively correlated with the abundances of Bacteroidetes and Proteobacteria. The addition of high concentration SAs inhibited the growth and reproduction of Firmicutes, resulting in the decrease of the content of tyrosine-like substance. The addition of 100 mg/L sulfaquinoxaline and sulfamethoxydiazine reduced the content of tyrosine-like by 47.5 % and 41.2 %, respectively. The change of tryptophan-like groups was opposite to that of the tyrosine-like. However, the addition of sulfamethoxazole had little effect on the content of all the abovementioned substances.

H2O2-assisted photocatalysis for removal of natural organic matter using nanosheet C3N4-WO3 composite under visible light and the hybrid system with ultrafiltration

In this study, a nano-sheet C3N4-WO3 composite (nsCW21) was applied as a visible-light active photocatalyst to degrade natural organic matter (NOM). The nsCW21 photocatalyst exhibited a higher removal efficiency for NOM than the bare host and other composite counterparts due to the effective separation of the charge carriers in the Z-scheme pathway. The addition of H2O2 resulted in the enhanced photocatalytic performance via the generation of hydroxyl radicals from the catalyst with an NOM removal rate of up to 71% for 5 h. The catalyst showed a considerable stability, which held a good NOM degradation efficiency during five cycle runs. The complex NOM removal behavior was unraveled by using a fluorescence excitation emission matrix-parallel factor analysis and a two-dimensional correlation spectroscopy (2D-COS) combined with Fourier-transform infrared spectroscopy (FT-IR). The large sized and the terrestrial humic-like component exhibited a high adsorption tendency toward the catalyst and was degraded primarily by h+, while a typical humic-like component, which is mainly removed by .OH, displayed a high degradation rate constant (k = 0.159 h−1). The 2D-COS revealed the sequence of the preferable removal among the different NOM functional groups in the nsCW21 system with H2O2 addition, which occurred in the order of open ring reaction > oxygenated functional groups > the transformation into aliphatic compounds/inorganic moieties. Meanwhile, the hybrid system that employed ultrafiltration as a post-treatment demonstrated synergetic effects on the improved effectiveness for NOM removal in the overall system, which was a total of 91%, of the residuals from the precedent photocatalysis as well as alleviating the membrane fouling.

Visible light-activated degradation of natural organic matter (NOM) using zinc-bismuth oxides-graphitic carbon nitride (ZBO-CN) photocatalyst: Mechanistic insights from EEM-PARAFAC

In this study, the complex degradation behavior of natural organic matter (NOM) was explored using photocatalytic oxidation systems with a novel catalyst based on a hybrid composite of zinc-bismuth oxides and g-C3N4 (ZBO-CN). The photooxidation system demonstrated the effective removal of NOM under low-intensity visible light irradiation, presenting removal rates of 53–74% and 65–88% on the basis of dissolved organic carbon (DOC) and the UV absorption coefficient (UV254), respectively, at 1.5 g/L of the catalyst. The NOM removal showed an increasing trend with a higher ZBO-CN dose. Comparative experiments with the hole and OH radical scavengers revealed that the direct oxidation occurring on the catalyst's surface might be the governing photocatalytic mechanism. Fluorescence excitation emission matrix-parallel factor analysis (EEM-PARAFAC) revealed the individual removal behavior of the different constituents in bulk NOM. Different tendencies towards preferential adsorption and subsequent oxidative removal were found among dissimilar fluorescent components within a bulk terrestrial NOM, following the order of terrestrial humic-like (C1) > humic-like (C2) > microbial humic-like (C3) components. The result suggests the dominant operation of π-π and/or hydrophobic interactions between the NOM and the catalyst. The discriminative removal behavior was more pronounced in visible light versus UV-activated systems, probably due to the incapability of visible light to excite è - h+ pairs of ZnO and the triplet state of NOM. The high photoactivity and structural stability of ZBO-CN under visible light implies its potential for an effective, low-cost and energy-saving treatment technology to selectively remove large sized humic-like substances from water.

Identification of textile wastewater in water bodies by fluorescence excitation emission matrix-parallel factor analysis and high-performance size exclusion chromatography

Identifying the causes of water body pollution is critical because of the serious water contamination in developing countries. The textile industry is a major contributor to severe water pollution due to its high discharge of wastewater with high concentrations of organic and inorganic pollutants. In this study, fluorescence excitation emission matrix-parallel factor (EEM-PARAFAC) analysis was applied to characterize textile industry wastewater and trace its presence in water bodies. The EEM spectra of textile wastewater samples collected from 12 wastewater treatment plants (WWTPs) revealed two characteristic peaks: Peak T1 (tryptophan-like region) and Peak B (tyrosine-like region). Two protein-like components (C1 and C2) were identified in the textile wastewater by PARAFAC analysis. The components identified from different textile WWTPs were considered identical (similarity >0.95). C1 and C2 were not sensitive to changes in pH, ionic strength, or low humic acid concentration (TOC < 4 mg/L). Therefore, C1 combined with C2 was proposed as a source-specific indicator of textile wastewater, which was further demonstrated by conducting high-performance size exclusion chromatography analysis. These results suggested that EEM-PARAFAC analysis is a reliable means of identifying textile wastewater pollution in water bodies and may also enable the identification of other industrial wastewater.

Unraveling complex removal behavior of landfill leachate upon the treatments of Fenton oxidation and MIEX® via two-dimensional correlation size exclusion chromatography (2D-CoSEC).

The complex removal behavior of stabilized landfill leachate was explored for the treatments of Fenton oxidation (FnO) and magnetic ion exchange (MIEX®) resin using two-dimensional correlation size exclusion chromatography (2D-CoSEC) and fluorescence excitation emission matrix-parallel factor analysis (EEM-PARAFAC). The overall removal rates of the bulk parameters (∼45% for dissolved organic carbon and ∼78% for UV absorbance) were similar between the two treatment options, while distinct differences were found with respect to different molecular sizes and chemical composition. The resin treatment eliminated humic substances (HS) and low molecular weight acid (LMWA) fractions to a greater extent than other fractions (i.e., HS: 62% and LMWA: 99%), while low molecular weight neutral (LMWN) and biopolymers (BP) fractions were more effectively treated by the FnO with the removal rates of 56% and 92%, respectively. The 2D-CoSEC further revealed that the sequential or preferential changes of different size fractions with increasing the resin or H2O2 were opposite between the two treatment options in the order of HS → LMWA → LMWN → BP for MIEX®. Due to their complementary roles in treating leachate, the combined processes removed a wider ranges of different molecular sizes compared to the single operation.