Characterization of dissolved organic matter using high-performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) with a multiple wavelength absorbance detector

Leaching of organic matter from cigarette butt filters as a potential disinfection by-products precursor

The study aimed to evaluate cigarette butt filters (CBFs) as a potential source of dissolved organic carbon (DOC) in water leading to the formation of disinfection by-products. Two different forms of CBFs - intact (I) and disintegrated (D), as they occur in the environment, were selected for leaching in chlorinated (CI, CD), non-chlorinated (NI, ND), and highly chlorinated (HCD) water samples. The UV absorbance profiles of the leachate samples showed that intact CBFs exhibited higher DOC leaching compared to the disintegrated ones, which was further accentuated in chlorinated samples (CI > CD > NI > ND). The Fourier Transform Infrared spectra of the leachates revealed the presence of characteristic functional groups of cellulose acetate and its chlorinated derivatives, indicating the potential degradation of the polymer. Moreover, trihalomethane (THM) formation in chlorinated samples was relatively higher in CI samples (2 - 11.5 times) compared to CD, consistent with the DOC leaching trends. Further, the speciation characteristics of different THMs in both CI and CD samples were similar. Although spectral and morphological analyzes of CI and CD samples revealed negligible variation, HCD samples depicted significant surface roughness characterized by the formation of pits and holes, along with the evolution of crystallinity. This suggested accelerated degradation of CBFs and disruption of acetyl groups as a factor of elevated chlorine concentrations.

Characterization and quantification of silver complexes with dissolved organic matter by size exclusion chromatography coupled to ICP-MS

The fate and behavior of silver in aquatic systems is intricately determined by its interactions with dissolved organic matter (DOM). In this study, we have introduced a method for identification and quantification of silver-DOM complexes using size exclusion chromatography-inductively coupled plasma mass spectrometry (SEC-ICP-MS). Our findings revealed that silver(I) was weakly bound to Suwannee River humic acid, fulvic acid, and natural organic matter (SRHA, SRFA, and SRNOM) in various media, resulting in facile dissociation during chromatographic separation. Suitable chromatographic conditions were determined for the elution of Ag-DOM complexes, involving the use of 0.5 mM ammonium acetate (pH 7) as the mobile phase and silver-aged column (pre-absorbing 0.1-0.7 μg silver(I)). SEC-UV and SEC-ICP-MS chromatograms revealed that Ag-binding fractions of DOM were dominated by its aromatic compounds. The quantification of silver-DOM complexes was achieved by SEC-ICP-MS combination with on-line isotope dilution. Silver at concentrations below 20 µg L-1 was mainly present in the form of organic complexes in low salinity water. These measurements aligned well with the results obtained using the equilibrium dialysis method. Species analyses of Ag-DOM complexes provide a deeper understanding of the reactivity, transport, and fate of silver in aquatic environments. ENVIRONMENTAL IMPLICATION: Ionic silver is highly toxic to aquatic organisms such as fish and zooplankton. The complexation of silver with binding sites within DOM significantly influences its speciation, mobility, and toxicity. Despite the complex and unknown structure of silver-DOM complexes, this study provided a SEC-ICP-MS method to identify and quantify these complexes in a range of media. By uncovering the formation of silver-DOM complexes across diverse media, this work enhances the comprehension of silver transformation processes and associated environmental risks in aquatic environments.

Stormwater discharge: An overlooked source of disinfection byproduct precursors

Discharge from the stormwater system is as an important pathway for contaminant transport, impacting the quantity and characteristics of dissolved organic matter (DOM) in surface water, and thus the formation of disinfection byproducts (DBPs) during downstream drinking water disinfection. In this study, DOM in stormwater pipes was characterized by size-exclusion chromatography, and the formation of 27 DBPs and halogen-specific total organic halogen (TOX) following chlorination was investigated. Overall, DOM in stormwater pipes was characterized by low molecular weight compounds and microbial-derived organics. Total DBP concentrations in chlorinated stormwaters were ∼1-15 times higher than in chlorinated surface waters. DBPs formed in stormwaters were dominated by trihalomethanes and haloacetic acids. Moreover, the DBP-associated toxicity of chlorinated stormwaters was ∼1-38 times higher than in chlorinated surface waters, and mainly due to the presence of large amount of haloacetaldehydes and haloacetonitriles. Sampling during a rainfall event suggested that stormwater discharge significantly increased DBP precursors in the surface water. The high formation and estimated toxicity of DBPs in stormwater discharge indicates this is an overlooked source of DBP precursors, posing a threat to the aquatic environment and potentially drinking water quality.

Nucleoside Analogs: A Review of Its Source and Separation Processes

Nucleoside analogs play a crucial role in the production of high-value antitumor and antimicrobial drugs. Currently, nucleoside analogs are mainly obtained through nucleic acid degradation, chemical synthesis, and biotransformation. However, these methods face several challenges, such as low concentration of the main product, the presence of complex matrices, and the generation of numerous by-products that significantly limit the development of new drugs and their pharmacological studies. Therefore, this work aims to summarize the universal separation methods of nucleoside analogs, including crystallization, high-performance liquid chromatography (HPLC), column chromatography, solvent extraction, and adsorption. The review also explores the application of molecular imprinting techniques (MITs) in enhancing the identification of the separation process. It compares existing studies reported on adsorbents of molecularly imprinted polymers (MIPs) for the separation of nucleoside analogs. The development of new methods for selective separation and purification of nucleosides is vital to improving the efficiency and quality of nucleoside production. It enables us to obtain nucleoside products that are essential for the development of antitumor and antiviral drugs. Additionally, these methods possess immense potential in the prevention and control of serious diseases, offering significant economic, social, and scientific benefits to the fields of environment, biomedical research, and clinical therapeutics.

Delimiting conditions under which natural organic matter can control Fe speciation and size in freshwaters

Pollutant and nutrient mobility in natural waters is typically controlled by sorption onto the high surface area of colloidal particles, most of which may form by precipitation of Fe(III)(hydr)oxides. Therefore, prediction of the speciation and size of Fe is critical to managing water quality. Prediction from pH and dissolved oxygen (D.O.) saturation can fail because of Fe binding to natural organic matter (N.O.M.) in natural waters. We test the influence of environmental variables -temperature, illumination and mixing order of Fe and N.O.M. with D.O.- on the impact of N.O.M.. Differences in mixing order simulate Fe(II) mixing with N.O.M. in groundwater prior to emerging, in comparison to Fe(II) emerging into oxic surface waters containing N.O.M.. Fe speciation and size were measured in waters containing N.O.M. with and without D.O., but also a water to which N.O.M. and then D.O. were added sequentially. Without D.O. free Fe(II) bound to N.O.M. and became a filterable particle. Binding increased with pH and at 7.5 was sufficient for Fe speciation in oxic waters to become influenced by whether mixing had been sequential or simultaneous. Therefore, at high pH Fe speciation in oxic surface waters requires knowledge of N.O.M. content of this water and upstream groundwaters. Cold (10 °C) decreased anoxic binding of Fe(II) to N.O.M. and both cold and darkness alsodecreased Fe binding to N.O.M. under oxic conditions, because in both cases Fe(III)(hydr)oxide surfaces out-compete N.O.M. for binding Fe. Cold and darkness therefore overwhelm the effect of mixing order on oxic Fe speciation, and cold even makes the presence or absence of N.O.M. irrelevant. In the cold or dark, prediction of Fe speciation and size in surface waters may not require knowledge of N.O.M. content of upstream groundwaters. Furthermore, when cold, prediction may not even require knowledge of N.O.M. content of the surface waters.

Unravelling relationships between fluorescence spectra, molecular weight distribution and hydrophobicity fraction of dissolved organic matter in municipal wastewater

The characteristics of dissolved organic matter (DOM) in the influent and secondary effluent from 6 municipal wastewater treatment plants (WWTPs) were investigated with a size exclusion chromatogram (SEC) coupled with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) as a function of molecular weight (MW). The SEC chromatograms showed that biopolymers (>6 kDa) and humic substances (0.5-6 kDa) comprised the significant fraction in the influent, while humic substances became the abundant proportion in the secondary effluent. Direct linkages between MW distribution and hydrophobicity of DOM in the secondary effluent were further explored via SEC analysis of XAD resin fractions. DON and DOC with different hydrophobicity exhibited significantly distinct MW distribution, indicating that it was improper to consider DOC as a surrogate for DON. Different from DOC, the order of averaged MW in terms of DON was hydrophobic neutral ≈ transphilic neutral > hydrophobic acid > transphilic acid > hydrophilic fraction. Fluorescence spectral properties exhibited a significant semi-quantitative correlation with MW and hydrophobicity of DOC, with Pearson's coefficients of -0.834 and 0.754 (p < 0.01) for biopolymer and humic substances. Meanwhile, regional fluorescence proportion was demonstrated to indicate the MW and hydrophobicity properties of DON at the semi-quantitative level. The fluorescence excitation-emission matrix (EEM) could be explored to provide a rapid estimation of MW distribution and hydrophobic/hydrophilic proportion of DOC and DON in WWTPs.

NOM fractionation by HPSEC-DAD-OCD for predicting trihalomethane disinfection by-product formation potential in full-scale drinking water treatment plants

Chlorination is a common method for water disinfection; however, it leads to the formation of disinfection by-products (DBPs), which are undesirable toxic pollutants. To prevent their formation, it is crucial to understand the reactivity of natural organic matter (NOM), which is considered a dominant precursor of DBPs. We propose a novel size exclusion chromatography (SEC) approach to evaluate NOM reactivity and the formation potential of total trihalomethanes-formation potentials (tTHMs-FP) and four regulated species (i.e. CHCl_3, CHBrCl_2, CHBr₂Cl, and CHBr₃). This method combines enhanced SEC separation with two analytical columns working in tandem and quantification of apparent molecular weight (AMW) NOM fractions using C content (organic carbon detector, OCD), 254-nm spectroscopic (diode-array detector, DAD) measurements, and spectral slopes at low (S_206-240) and high (S_350-380) wavelengths. Links between THMs-FP and NOM fractions from high performance size exclusion chromatography HPSEC-DAD-OCD were investigated using statistical modelling with multiple linear regressions for samples taken alongside conventional full-scale as well as full- and pilot-scale electrodialysis reversal and bench-scale ion exchange resins. The proposed models revealed promising correlations between the AMW NOM fractions and the THMs-FP. Methodological changes increased fractionated signal correlations relative to bulk regressions, especially in the proposed HPSEC-DAD-OCD method. Furthermore, spectroscopic models based on fractionated signals are presented, providing a promising approach to predict THMs-FP simultaneously considering the effect of the dominant THMs precursors, NOM and Br^-.

Provenances, preponderances, and distribution of humic acids and organic pollutants in hydro-geosphere: The co-existence, interaction and isotopic biomarkers in the riverine ecosystem

This paper aims to critically review the importance of geochemical fingerprinting and tracing using biomarkers and stable isotopes in the riverine ecosystem and depicts that isotopic ratios of δ¹³C, δ¹⁵N, and δ³⁴S can be used for tracing pollution sources. Stable isotopes like carbon, hydrogen, nitrogen, oxygen, and sulfur are being used for this purpose, and their isotopic signatures are primarily used to distinguish close sources of organic matter through dual isotopes. The present review is articulated to bridge the critical research gaps of the previous and contemporary documented literature on the genesis and transport of OM between freshwater and marine systems. This review comprehensively provides methods and techniques in geochemical tracing and discusses the future directions to address the challenges of the current methods to enhance the knowledge about the source identification of organic matter in the riverine environment. Tracer geochemistry emphasizes the implications of elemental abundances and isotope ratio variations in geologic substances to track natural earth processes, anthropogenic contaminants, and geochemical signatures in the hydrologic system. The principal constituent of organic matter comprises humic substances like humic acid, fulvic acid, and humin, and these comprise 50-75% of the sediments and DOC in natural waters. Their structural and functional characterization is required to elucidate the transport and fate of organic matter, which are often influenced by several paleoenvironmental factors.

Transport of Veterinary Antibiotics in Farmland Soil: Effects of Dissolved Organic Matter

The application of manure as a fertiliser to farmland is regarded as a major source of veterinary antibiotic (VA) contamination in the environment. The frequent detection of such emerging contaminants and their potential adverse impacts on the ecosystem and human health have provoked increasing concern for VA transport and fate. Extrinsic dissolved organic matter (DOM) may be introduced into farmland soil along with Vas, and thus exert significant effects on the transport of VAs via hydrological processes upon rainfall. The leaching of VAs can be either enhanced or reduced by DOM, depending on the nature, mobility, and interactions of VAs with DOM of different origins. From the aspect of the diversity and reactivity of DOM, the state-of-the-art knowledge of DOM-VA interactions and their resulting effects on the sorption-desorption and leaching of VAs in farmland soil was reviewed. Spectroscopic techniques for examining the extent of binding and reactive components of DOM with VAs are summarized and their usefulness is highlighted. Models for simulating VA transport under the effects of DOM were also reviewed. It is suggested that distinct impacts of DOM of various organic fertiliser/amendment origins should be considered for predicting the transport of VAs in farmland soil.

Application of UV-vis absorption spectrum to test the membrane integrity of Membrane bioreactor (MBR)

In this work, UV-vis absorption spectrum of the membrane integrity analysis based on slopes of log-transformed absorbance spectra, differential absorbance spectroscopy (DAS), and absorption coefficient α(254) were studied at different number of breakage fibers and filtration times. Moreover, we analyze the influence of Fe²⁺ and Ca²⁺concentration on UV spectrum detection results. Cluster analysis and the change ratio R_s were used to determine the dissolved organic matter (DOM) leakage stages. As a result, the correlation coefficient between slope_280-350 value and the number of breakage fibers is 0.901. Seven gaussian bands were successfully model from the DAS, and A4 (312 nm), A5 (339 nm), A6 (367 nm) were chosen to indicate the extent of breakage fiber. Peak 4(A4) is minimally affected by ions concentration. The α(254) could be used as a good indicator for detecting industrial wastewater treatment process which correlation coefficient between the number of breakage fibers is 0.955. The DOM leakage process was divided into three stages which were bulk leakage stage, development stage and stabilization stage. The UV-vis absorption spectrum can effectively detect the membrane integrity more sensitive than particle counter and three analyse methods are suitable for different substance in feed water.

Applying synchronous fluorescence and UV-vis spectra combined with two-dimensional correlation to characterize structural composition of DOM from urban black and stinky rivers

UV-visible spectroscopy and synchronous fluorescence spectroscopy (SFS) combined with two-dimensional correlation spectroscopy (2D-COS) were applied for extracting fluorescence components, tracing organic functional groups, and revealing variations of dissolved organic matter (DOM) in Puhe River. Water samples were collected from the mainstream and two tributaries (Nanxiaohe River and Huangnihe River). DOM in three rivers was composed of protein-like fluorescent (PLF), microbial humus-like fluorescent (MHLF), fulvic-like fluorescent (FLF), and humic-like fluorescent components, which were relative to aromatic groups, phenolic groups, carboxylic groups, and microbial products. The PLF and MHLF were dominated in DOM fractions in the rivers, and the average content of the PLF was the highest in Nanxiaohe River. Humification degree of DOM was the highest in Puhe River, followed by Huangnihe River and Nanxiaohe River. However, molecular mass of DOM in Puhe River was the lowest, followed by Huangnihe River and Nanxiaohe River. Based on the 2D-COS of the SFS and UV-visible spectra, the variation order of DOM fractions in Puhe River was PLF → MHLF → FLF, and the PLF was consistent with the phenolic groups, aromatic groups, and carboxylic groups, but the adverse trend with the microbial products. The variation order in Nanxiaohe River was MHLF → PLF → FLF, and the MHLF was consistent with the aromatic groups, phenolic groups, carboxylic groups, and microbial products. The variation order in Huangnihe River was MHLF → PLF → FLF too, and the PLF was consistent with the carboxylic groups and aromatic groups. The results of the present study demonstrate that UV-visible spectroscopy and SFS combined with 2D-COS are useful methods to characterize structural composition of DOM from urban black and stinky rivers so as to investigate their pollution status.

Spatial intensity distribution model of fluorescence emission considering the spatial attenuation effect of excitation light

The fluorescence quantitative analysis method of a solution is widely applied in chemical analysis, clinical medicine testing, environmental monitoring, food safety detection, and so on. It is based on the linear relationship between the intensity of fluorescence emission and the concentration of the substance in solution. Without consideration of the spatial attenuation effect of excitation light, it is applied only to a dilute solution. In this research, a fluorescence emission model is established based on the interaction and propagation law between the excitation light and the fluorescent substances. The spatial attenuation effect of excitation light is analyzed by an element analysis method, and the spatial intensity distribution of fluorescence is revealed. Further, a high accuracy model between the received fluorescence intensity and concentration is obtained. Applications of this model and further design will allow for high throughput fluorescence analysis and the analysis of fluorescent substances with ultra-wide range concentration, such as on-line testing fluorescent dyes in the textile industry, monitoring protein plasma in biomedical field, and high-throughput DNA fluorescence analysis etc. As an example, based on this model, an ultra-wide concentration range (0.02 - 250 mg/L) detection of tryptophan with high accuracy (R² = 0.9994, RRMSE = 0.0356) is realized.

Advances in the characterization and monitoring of natural organic matter using spectroscopic approaches

Natural organic matter (NOM) is ubiquitous in environment and plays a fundamental role in the geochemical cycling of elements. It is involved in a wide range of environmental processes and can significantly affect the environmental fates of exogenous contaminants. Understanding the properties and environmental behaviors of NOM is critical to advance water treatment technologies and environmental remediation strategies. NOM is composed of characteristic light-absorbing/emitting functional groups, which are the "identification card" of NOM and susceptive to ambient physiochemical changes. These groups and their variations can be captured through optical sensing. Therefore, spectroscopic techniques are elegant tools to track the sources, features, and environmental behaviors of NOM. In this work, the most recent advances in molecular spectroscopic techniques, including UV-Vis, fluorescence, infrared, and Raman spectroscopy, for the characterization, measurement, and monitoring of NOM are reviewed, and the state-of-the-art innovations are highlighted. Furthermore, the limitations of current spectroscopic approaches for the exploration of NOM-related environmental processesand how these weaknesses/drawbacks can be addressed are explored. Finally, suggestions and directions are proposed to advance the development of spectroscopic methods in analyzing and elucidating the properties and behaviors of NOM in natural and engineered environments.

The role of interactions between extracellular organic matter and humic substances on coagulation-ultrafiltration process

Removals of extracellular organic matter (EOM) derived from cyanobacterium M. aeruginosa and humic acid (HA) in single-component and bi-component systems and the interactions during the coagulation-ultrafiltration (C-UF) process were investigated in this study. In a single-component system, only 23% EOM could be removed by alum at dose as high as 6 mg/L, which induced serious membrane fouling in the following UF process. Interestingly, higher EOM removal efficiency was achieved (increase by about 20%) with the existence of HA and EOM-HA achieved less decline of permeate flux compared with individual EOM C-UF process. Zeta potential and Fourier transform infrared spectroscopy analysis indicated that the interactions of HA and EOM can strengthen charge neutralization and reduce CH₂ chemical bonds, which had a positive effect on the coagulation process. In addition, EOM-HA floc had a more open and looser structure than EOM floc, which was more favorable in the UF process. The extended Derjaguin-Landau-Verwey-Overbeek theory indicated that the acid-base interaction energy was mainly reduced, thereby alleviating membrane fouling. The study showed this beneficial interaction between the HA and EOM would enhance the EOM removal efficacy by coagulation and release the membrane fouling caused by EOM.

Removal efficiency of dissolved organic matter from secondary effluent by coagulation-flocculation processes

Wastewater reuse has been widely discussed as an essential strategy to minimize the consumption of drinking water for less noble purposes. During biological wastewater treatment, organic matter is converted into a complex matrix containing a variety of soluble organic compounds. The objective of the present study was to evaluate the removal efficiency of the residual organic load in the final effluent from wastewater treatment plant with a conventional activated sludge process by different coagulants and parameters of coagulation-flocculation process, using dissolved organic carbon (DOC) concentration, molecular weight (MW) size distribution by size exclusion chromatography (SEC) coupled to mass spectrometry (MS), and zeta potential (ZP) analyses. The results showed a DOC removal efficiency up to 45% with iron chloride, and of 38% for aluminum sulfate and 31% for PAC coagulants. ZP was also measured during the procedures and authors conclude that the ZP also does not have a determining role in these removals. SEC and MS assessment was able to detect changes on secondary effluent molecular weight distribution profile after effluent coagulation-flocculation, this technique might be a promising tool to understand the composition of effluent organic matter and be helpful to estimate and optimize the performance of wastewater effluents treatment processes.

Evaluation of aliphatic/aromatic compounds and fluorophores in dissolved organic matter of contrasting natural waters by SEC-HPLC with multi-wavelength absorbance and fluorescence detections

The analytical high performance size exclusion liquid chromatography (SEC-HPLC) with multi-wavelength absorbance and fluorescence detections and fluorescence 3D-excitation/emission matrix (EEM) were used for the analysis of average molecular size (MS), molecular size distribution of aliphatic/aromatic compounds and fluorophores in dissolved organic matter (DOM) from Suwannee River (SRDOM) and two Karelian lakes (Vodoprovodnoe Lake - L1DOM and Onego Lake - L2DOM). The average MS of DOM samples varied in the order SRDOM > L1DOM > L2DOM. The absorbance ratios A250/A365 and A210/A254 have been used for the DOM samples characterization. The absorbance ratio A250/A365 provided significant information about average MS of the bulk aquatic DOMs but was not exactly correlated with the results of SEC-HPLC data. The absorbance ratio A210/A254 in combination with SEC was well correlated with the content of DOM aliphatic/aromatic compounds and could be used as an important water quality index to estimate the level of protein-like material in the aquatic DOM. Regardless of the origin (river or lakes), different geographical locations and different average MS of DOM, several similar types of humic-like SEC-separated fluorophores were found within the samples. In all DOM samples the decrease of the fluorophores emission maxima paralleled the decrease of their relative MS. The combination of SEC-HPLC with multi-wavelength fluorescence and absorbance detection and EEM analyses appears very useful for DOM characterization and for tracking of microbial activity resulting from anthropogenic and/or eutrophic impact in aquatic environments.

Emerging investigator series: critical review of photophysical models for the optical and photochemical properties of dissolved organic matter

Optical measurements (absorbance and fluorescence) are widely used to track dissolved organic matter (DOM) quantity and quality in natural and engineered systems. Despite many decades of research on the optical properties of DOM, there is a lack of understanding with regards to the underlying photophysical model that is the basis for these optical properties. This review both summarizes advances to date on the photophysical properties of DOM and seeks to critically evaluate the photophysical models for DOM optical properties. Recent studies have refined the quantitative understanding of DOM photophysical properties such as excited state lifetimes and energies, rates of different photophysical processes, and quantum yields. Considering fundamental models, more clarity is needed on whether DOM photophysical processes are due to a superposition of non-interacting components (superposition model), or whether a portion of optical signals can be ascribed to electronically interacting moieties, for example in the form of electron donor-acceptor complexes (charge transfer model). Multiple studies over more than two decades have provided evidence for the charge transfer model. Questions have been raised, however, about the broad applicability of the charge transfer model. The charge transfer and superposition model are critically reviewed in light of this current research. Recommendations are given for future studies to help clarify the accuracy of these competing photophysical models.

Characterizing the molecular weight distribution of dissolved organic matter by measuring the contents of electron-donating moieties, UV absorbance, and fluorescence intensity

Electron-donating moieties (EDM) have recently been used to characterize the redox properties and treatability of dissolved organic matter during water and wastewater treatment. In this study, size exclusion chromatography followed by a derivatization-spectrometric method was developed to determine the molecular weight (MW) distribution of EDM in dissolved organic matter. The relationships between EDM concentration and chromophore content (indicated by UVA₂₅₄), fluorophore content (indicated by fluorescence), and dissolved organic carbon (DOC) concentration were analyzed for different MW fractions. In general, natural organic matter (NOM) showed higher total EDM concentration and higher EDM average MW than effluent organic matter (EfOM). For NOM, fractions with MW between 1.8 k and 6.9 k Da accounted for most of the EDM (45.4%-48.6%), followed by the fractions with MW < 1.8 k Da (25.6%-42.4%). By contrast, the EDM in EfOM occurred predominantly in fractions with MW < 1 k Da (51.8%-58.6%), with lower concentrations in fractions with MW > 1.8 k Da (<20.2%). The heterogeneous MW distribution of EDM was strongly correlated to the presence of chromophores, but not DOC or fluorophores. The EDM difference between MW fractions suggested that the fraction with MW 1.8-6.9 k Da (40.7%-47.1%) and the fractions with MW < 1 k Da (50.2%-58.8%) should be the dominant oxidant consumers in NOM and EfOM, respectively. When the EDM was normalized by the DOC for each MW fraction (EDM_MW/DOC_MW), the EDM_MW/DOC_MW of relatively high-MW fractions (>1.8 k Da) is 1.2-1.9 times of relatively low-MW (<1 k Da) fractions for both NOM and EfOM, which indicates that higher-MW fractions are more susceptible to chemical oxidations. The relationship between EDM change and UVA₂₅₄ change varied for different MW fractions during advanced ozonation treatment, because of the different oxidation mechanisms in operation for MW fractions. The ozonation of EfOM fractions with higher MW (>1.8 k Da) and lower MW (<1 k Da) preferentially resulted in benzoquinone formation and ring-cleavage, respectively.

Characterizing property and treatability of dissolved effluent organic matter using size exclusion chromatography with an array of absorbance, fluorescence, organic nitrogen and organic carbon detectors

In this study, size exclusion chromatography with an array of absorbance, fluorescence, organic nitrogen and organic carbon detectors was used for characterizing property and treatability of effluent organic matter (EfOM) from 12 wastewater treatment plants. According to their apparent molecular weight (AMW), EfOM fractions were assigned to biopolymers (>20 kDa), humic substances that comprise sub-fractions of humic-like acids (HA-I & HA-II, 2.3-7.0 kDa) and fulvic-like acids (FA, 1.5-2.3 kDa), building blocks (0.55-1.5 kDa) and low molecular weight neutral substances (<550 Da). The fractions of biopolymers and low molecular weight neutral substances didn't show humic-like fluorescence, while the fractions of HA-II, FA and building blocks usually had signatures of both humic-like and protein-like fluorescence. Humic substances generally contributed the largest proportion of dissolved organic carbon and nitrogen (DOC & DON) in effluents. Coagulation removed EfOM fractions following the order of biopolymers > HA subfraction > FA subfraction > building blocks, while little removal of protein-like fluorescence in HA-II and FA subfractions was detected. Anion exchange treatment could effectively reduce DOC and DON concentrations; the sequence of the treatment efficiency was humic substances > biopolymers > building blocks. Increasing O₃ doses caused DOC and DON of EfOM to be gradually transformed from large AMW fractions into small AMW fractions, while chromophores and fluorophores in HA subfractions were relatively more refractory than those in the other fractions. Size exclusion chromatography with multiple detectors are suggested to be an informative technique for estimating treatability of EfOM by advanced wastewater treatment processes.

Detection of humic acid in water using flat-sheet and folded-rod viscous alkaline glucose syrups

Interaction of the alkaline glucose solution with humic acid.

Characterization of aquatic organic matter: Assessment, perspectives and research priorities

Organic matter (OM) refers to the largest reactive reservoir of carbon-based compounds on Earth. Aside of its role as a source of carbon, OM is also actively involved in a wide range of ecological functions. It also plays an important role in the solubility, toxicity, bioavailability, mobility and distribution of pollutants. Therefore, OM is a key component in the local and global carbon cycle. About 12,000 articles containing organic matter in the title were published during the past decade, with a continuous increasing number each year (ISI Web of Science). Although this topic was widely explored and its interest has significantly increased, some limitations remain. These limitations can be technical (e.g., pre-treatment processes, low-resolution instrument, data handling) and can be related to the current approach. In this review, we first present the current strategies and tools to characterize the organic matter in the aquatic environment, then we tackle several aspects of current characterization limitations. Finally, we suggest new perspectives and priorities of research to improve the current limitations. From our point of view, simultaneous studies of particulate and dissolved OM fractions should be prioritized and multi-disciplinary approach, creation of databases, controlled experiments and collaborative works should be the next targets for future OM research priorities.

Redox properties and dechlorination capacities of landfill-derived humic-like acids

Electron transfer capacities (ETC) of humic-like acids (HLA) and their effects on dechlorination are dependent on their redox-active properties. Aging and minerals can affect the chemical compositions and structures of HLA. However, the underlying mechanism and the impacts on the dechlorination capacities of HLA are poorly understood. We investigated how redox properties change in association with the intrinsic chemical natures and exterior minerals of the HLA extracted from landfilled solid wastes. Furthermore, the ETC of the landfill-derived HLA could be strengthened by increasing landfill age and demineralization, thereby facilitating the dechlorination of pentachlorophenol (PCP). The HLA molecules started to polymerize aromatic macromolecules during landfilling, leading to an increase in ETC and dechlorination capacities. Macromolecular HLA were dissociated to smaller molecules and exposed more aromatic and carboxyl groups when separated from minerals, which enhanced the ETC and the dechlorination abilities of the HLA. Microbial-mediated dechlorination was an effective way to degrade PCP, and almost 80% of the PCP was transformed after 40 days of demineralized HLA and Shewanella oneidensis MR-1 incubation. The demineralization and aging further facilitated the microbial-mediated PCP dechlorination. The findings provide a scientific base for improving in-situ bioremediation of chlorinated compound-contaminated soils using freshly synthesized HLA.

A Rapid Fenton treatment of bio-treated dyeing and finishing wastewater at second-scale intervals: kinetics by stopped-flow technique and application in a full-scale plant

A rapid Fenton treatment at second-scale intervals was investigated for further removal of organic compounds in the effluent of bio-treated dyeing and finishing wastewater (BDFW). The decolorization kinetics was studied using a stopped-flow spectrophotometer (SFS) at second-scale intervals. A combined first-order model was found to fit well for the decrease of both methylene blue and rhodamine B in SFS as well as SCOD (soluble chemical oxygen demand) and DOC (dissolved organic carbon) in real BDFW in batch test during Fenton oxidation. A full-scale plant with treatment capacity of 400,000 m³·d⁻¹ was designed and has been run continuously based on the results of the stopped-flow study to treat the effluent of BDFW using Fenton oxidation in 16 pipeline reactors, each with a volume of 6.9 m³ and 24 s of reaction time since 2014. The COD, SCOD and DOC decreased from 140, 110 and 35 mg·L⁻¹ to 77, 71 and 26 mg·L⁻¹ respectively, which can meet the latest strict discharge limitations. The natural fluorescent substances detected in the BDFW were completely removed. The main organic pollutants in the BDFW can be significantly reduced using both gas chromatography-mass spectrometry and ultrahigh-performance liquid chromatography-hybrid quadrupole time-of-flight mass spectrometry. The rapid Fenton reaction applied in pipeline reactors at second intervals has several advantages over the conventional Fenton’s process such as much shorter reaction time at second scale intervals, no need to build extra pH adjustment or reaction tanks, simple operation, low capital cost, etc.

Multi-spectral characterization of natural organic matter (NOM) from Manitoba surface waters using high performance size exclusion chromatography (HPSEC)

The main objective of this research was to develop an algorithm that would be able to relate ultraviolet absorbing moieties in potable water to trihalomethanes (THMs) and other water quality parameters. The characterization was carried out using high performance size exclusion chromatography (HPSEC) to separate water samples based on apparent molecule weight (AMW); while the developed algorithm utilized multi-spectral information extracted from 7 Manitoba source waters, and from samples treated with strong base ion-exchange (IX). AMW components between 2.2-4 k Da were strongly associated with the formation of THMs, and more strongly with chlorinated byproducts, determined using Spearman and Pearson coefficients. associations were not improved upon removal of the raw samples from the dataset, indicating that the applied methodology is not specific to IX treatment. Strong associations were also found between initial wavelengths of 226-239 nm and final wavelengths of 257-273 nm, which suggests that absorbing moieties in these ranges are prime precursors in the reaction mechanism to form THMs. A closer look noted that chlorinated THMs were more strongly associated than THMs in general; with brominated byproducts following closely to profiles of UV₂₅₄ - indicating these parameters are closely related.

A new molecular weight (MW) descriptor of dissolved organic matter to represent the MW-dependent distribution of aromatic condensation: Insights from biodegradation and pyrene binding experiments

In this study, we utilized a size exclusion chromatography (SEC) system that was equipped with a fluorescence emission scanning mode to explore the heterogeneous distribution of the humification index (HIX) values within bulk dissolved organic matter (DOM). The HIX-based SEC chromatograms showed that the molecular weight (MW)-dependent distribution of aromatic condensation was heavily affected by the DOM sources and the progress of biodegradation. The HIX heterogeneity across different MW was more pronounced for terrestrial versus aquatic DOM sources. Microbial incubation of leaf litter DOM led to the initial enhancement of the HIX at a relatively low MW, followed by a gradual increase at larger MW values. The dynamic changes of the HIX can be attributed to (1) the preferential removal of non-aromatic or less-aromatic molecules by microorganisms, (2) the production of microbial metabolites, (3) microbial humification, and (4) self-assemblage of humic-like molecules. From the SEC chromatograms, the HIX-based average molecular weight (or MW_HIX) was proposed as a unifying surrogate to represent an MW that was highly associated with aromatic condensation. The MW_HIX discriminated four different DOM sources and described well the biodegradation-induced changes. The MW_HIX also presented a good positive correlation with pyrene organic carbon-normalized binding coefficients (K_oc). The prediction capability of the MW_HIX for pyrene K_oc was higher than those based on the single descriptors of bulk DOM, such as HIX and MW, which revealed its superior linkage with the DOM reactivity related to both MW and HIX.

Diethyl phenylene diamine (DPD) oxidation to measure low concentration permanganate in environmental systems

Permanganate has been used traditionally in drinking water treatment for its oxidation properties and ease of use. The concentration of permanganate in treatment conditions is low and difficult to detect. A colorimetric method using diethylphenylene diamine (DPD) oxidation to measure low levels (i.e., less than 6 μM) of permanganate in water was developed and applied to quantify permanganate scavenging by dissolved organic matter (DOM). Manganese dioxide (MnO₂) particles were shown to interfere with DPD oxidation; however, particles were removed effectively using 0.1 μm PVDF filters prior to reaction with DPD. DOM and complexed-Mn(III) were concluded to not interfere with the DPD reaction. The DPD method was validated by obtaining the second-order rate constant for permanganate reaction with phenol (1.7 ± 0.2 M^-1 s^-1), and comparing to the rate constant obtained independently by monitoring phenol degradation (i.e., UPLC-UV) (1.6 ± 0.2 M^-1 s^-1). Permanganate reaction with DOM isolate samples did not follow pseudo-first order kinetics. Faster reaction rates were observed with higher ionic strength (1 mM versus 5 mM carbonate). No change in reaction rates with pH was observed at lower ionic strength (1 mM); while at higher ionic strength, the reaction rate was faster at pH 7 than at pH 10. In contrast, linear kinetics were observed for permanganate reaction with DOM in filtered whole water samples. These samples showed similar trends with pH and ionic strength as for DOM isolates. The presented method is valid to quantify permanganate reaction rates with organic contaminants or with natural scavengers.

An overview of the uses of high performance size exclusion chromatography (HPSEC) in the characterization of natural organic matter (NOM) in potable water, and ion-exchange applications

Natural organic matter (NOM) constitutes the terrestrial and aquatic sources of organic plant like material found in water bodies. As of recently, an ever-increasing amount of effort is being put towards developing better ways of unraveling the heterogeneous nature of NOM. This is important as NOM is responsible for a wide variety of both direct and indirect effects: ranging from aesthetic concerns related to taste and odor, to issues related to disinfection by-product formation and metal mobility. A better understanding of NOM can also provide a better appreciation for treatment design; lending a further understanding of potable water treatment impacts on specific fractions and constituents of NOM. The use of high performance size-exclusion chromatography has shown a growing promise in its various applications for NOM characterization, through the ability to partition ultraviolet absorbing moieties into ill-defined groups of humic acids, hydrolysates of humics, and low molecular weight acids. HPSEC also has the ability of simultaneously measuring absorbance in the UV-visible range (200-350 nm); further providing a spectroscopic fingerprint that is simply unavailable using surrogate measurements of NOM, such as total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV₂₅₄), excitation-emission matrices (EEM), and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄). This review mainly focuses on the use of HPSEC in the characterization of NOM in a potable water setting, with an additional focus on strong-base ion-exchangers specifically targeted for NOM constituents.

Monitoring WWTP performance using size-exclusion chromatography with simultaneous UV and fluorescence detection to track recalcitrant wastewater fractions

A trial monitoring of a typical full-scale municipal WWTP in Central Finland was aimed to explore applicability of high performance liquid chromatography - size exclusion chromatography (HPSEC) with simultaneous UV and fluorescence detection as a tool for advanced routine monitoring of wastewater treatment. High, intermediate, and low molecular weight (MW) fractions of untreated wastewater (influent) and treated wastewater (secondary effluent) were characterized in terms of UV absorbance at 254 nm (UVA₂₅₄) and specific fluorescence representing tyrosine-like, tryptophan-like, and humic/fulvic-like compounds. The activated sludge treatment removed 97 ± 1% of BOD, 93 ± 2% of COD, 71 ± 7% of DOC, and 24 ± 7% of TN, while the overall reduction of UVA₂₅₄ was 50 ± 6%. Total fluorescence signal declined by ∼80% for tyrosine-like, by 60-70% for tryptophan-like, and by 7-36% for humic/fulvic-like compounds. Low and intermediate MW humic/fulvic-like compounds fluorescing at λ_ex/λ_em = 390/500 nm demonstrated recalcitrant behavior. Protein-like and humic/fulvic-like fractions of low MW < 1 kDa accounted for 60-65% of total UVA₂₅₄ and 50-70% of total fluorescence of whole influent and effluent samples. Strong linear correlations were observed between wastewater BOD, COD, DOC, UVA₂₅₄ and tyrosine-like, tryptophan-like fluorescence.

Dynamic Intermolecular Interactions Control Adsorption from Mixtures of Natural Organic Matter and Protein onto Titanium Dioxide Nanoparticles

Engineered nanoparticles (NPs) will obtain macromolecular coatings in environmental systems, changing their subsequent interactions. The matrix complexity inherent in natural waters and wastewaters greatly complicates prediction of the corona formation. Here, we investigate corona formation on titanium dioxide (TiO₂) NPs from mixtures of natural organic matter (NOM) and a protein, bovine serum albumin (BSA), to thoroughly probe the role of mixture interactions in the adsorption process. Fundamentally different coronas were observed under different NP exposure conditions and time scales. In mixtures of NOM and protein, the corona composition was kinetically determined, and the species initially coadsorbed but were ultimately limited to monolayers. On the contrary, sequential exposure of the NPs to pure solutions of NOM and protein resulted in extensive multilayer formation. The intermolecular complexation between NOM and BSA in solution and at the NP surface was the key mechanism controlling these distinctive adsorption behaviors, as determined by size exclusion chromatography (SEC) and in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Overall, this study demonstrates that dynamic intermolecular interactions and the history of the NP surface must be considered together to predict corona formation on NPs in complex environmental media.

Characterization of isolated fractions of dissolved organic matter derived from municipal solid waste compost

Understanding the heterogeneous evolution characteristics of dissolved organic matter fractions derived from compost is crucial to exploring the composting biodegradation process and the possible applications of compost products. Herein, two-dimensional correlation spectroscopy integrated with reversed-phase high performance liquid chromatography and size exclusion chromatography were utilized to obtain the molecular weight (MW) and polarity evolution characteristics of humic acid (HA), fulvic acid (FA), and the hydrophilic (HyI) fractions during composting. The high-MW humic substances and building blocks in the HA fraction degraded faster during composting than polymers, proteins, and organic colloids. Similarly, the low MW acid FA factions transformed faster than the low weight neutral fractions, followed by building blocks, and finally polymers, proteins, and organic colloids. The evolutions of HyI fractions during composting occurred first for building blocks, followed by low MW acids, and finally low weight neutrals. With the progress of composting, the hydrophobic properties of the HA and FA fractions were enhanced. The degradation/humification process of the hydrophilic and transphilic components was faster than that of the hydrophobic component. Compared with the FA and HyI fractions, the HA fraction exhibited a higher MW and increased hydrophobicity.

Molecular Size Distribution of Fluorophores in Aquatic Natural Organic Matter: Application of HPSEC with Multi-Wavelength Absorption and Fluorescence Detection Following LPSEC-PAGE Fractionation

Analytical high performance size exclusion liquid chromatography (HPSEC) with multiwavelength absorbance and fluorescence detections was used for the analysis of molecular size distribution and optical properties of dissolved natural organic matter. Experiments were conducted on Suwannee River organic matter (SRNOM) and its fractions A, B, C+D preliminary obtained by combination of preparative low pressure size exclusion chromatography and polyacrylamide gel electrophoresis (LPSEC-PAGE) and purified by dialysis on membrane with nominal cutoff 10 kDa, the fractions molecular size varied in order A > B > C + D > 10 kDa. The multistep fractionation of SRNOM enabled the size-separation of at least five types of humic-like fluorophores within NOM showing emission maxima at 465, 450, 435, 420, and 405 nm. The decrease of the humic-like emission maxima paralleled the decrease of the nominal molecular size of fluorescent SRNOM. The protein-like fluorescence was split into tyrosine-like and tryptophan-like fluorophores and only detected in fractions A and B. This work provides new data on the optical properties of size-fractionated NOM, which consistent with the formation of supramolecular NOM assemblies, likely controlled by association of low-molecular size components. It is clearly observed for the high molecular size fraction A, containing free amino acids or short peptides. The combination of several different fractionation procedures is very useful for obtaining less complex NOM compounds and understanding the NOM function in the environment.

Fenton treatment of bio-treated fermentation-based pharmaceutical wastewater: removal and conversion of organic pollutants as well as estimation of operational costs

The Fenton process is used as a tertiary treatment to remove organic pollutants from the effluent of bio-treated pharmaceutical wastewater (EBPW). The optimal and most appropriate Fenton conditions were determined by an orthogonal array test and single-factor experiments. The removal of chemical oxygen demand (COD) was influenced by the following factors in a descending order: H₂O₂/Fe(II) molar ratio > H₂O₂ dosage > reaction time. Under the most appropriate Fenton conditions (H₂O₂/Fe(II) molar ratio of 1:1, H₂O₂ dosage of 120 mg L^-1 and reaction time of 10 min), the COD and dissolved organic carbon (DOC) were removed with efficiencies of 62 and 53%, respectively, which met the national discharge standard (GB 21903-2008) for the Lake Tai Basin, China. However, the Fenton treatment was inadequate for removal of N compounds, and the removal of organic nitrogen led to an increment in N-NH₃ from 3.28 to 19.71 mg L^-1. Proteins and polysaccharides were completely removed, and humic acids (HAs) were partly removed with an efficiency of 55%. Three-dimensional excitation/emission matrix spectra (3DEEMs) indicated complete removal of fulvic acid-like substances and 90% reduction in the florescence intensity of humic acid-like substances. Organic pollutants with molecular weights (MW) > 10 kDa were completely removed, MW 5-10 kDa were degraded into smaller MW ones, and some low molecular weight acids (MW 0.1-1 kDa) were mineralized during the Fenton process. Some species, including pharmaceutical intermediates and solvents were detected by gas chromatography-mass spectrometry (GC-MS). The operational costs of the Fenton's treatment were estimated to be 0.58 yuan RMB/m³ EBPW based on reagent usage and iron sludge treatment and disposal.

Influence of operational conditions on the stability of aerobic granules from the perspective of quorum sensing

Integrated aerobic granules were first cultivated in two sequencing batch reactors (SBRs) (A1 and A2). Then, A1's influent organic loading rate (OLR) was changed from alternating to constant (cycling time was still 6 h), while A2's cycling time varied from 6 to 4 h (influent OLR strategy remained alternating). After 30-day operation since the manipulative alternations, granule breakage happened in two reactors at different operational stages, along with the decrease of granule intensity. Granule diameter in A1 declined from the original 0.84 to 0.32 cm during the whole operation, while granules in A2 dwindled to 0.31 cm on day 22 with similar size to A1. Both the amount of total extracellular polymeric substances (EPSs) and the protein were declining throughout the operation, and the large molecular weight of protein was considered closely related to the stability of aerobic granules. The relative AI-2 level decreased at the same time, and influent OLR strategy might had more evident impact on quorum sensing (QS) ability of sludge compared with starvation period. Combined with microbial results, the decline of total EPS amount in two reactors could be concluded as follows: During the reactor operation, some functional bacteria gradually lost their dominance and were eliminated from the reactors, which finally caused granule disintegration. In summary, the results further confirmed that alternating OLR and proper starvation period were two major factors in effective cultivation and stability of aerobic granules from the perspective of QS.

Effect of nitrogen/phosphorus concentration on algal organic matter generation of the diatom Nitzschia palea: Total indicators and spectroscopic characterization

Critical algal blooms in great lakes increase the level of algal organic matters (AOMs), significantly altering the composition of natural organic matters (NOMs) in freshwater of lake. This study examined the AOM's characteristics of Nitzschia palea (N. palea), one kind of the predominant diatom and an important biomarker of water quality in the great lakes of China, to investigate the effect of AOMs on the variation of NOMs in lakes and the process of algal energy. Excitation-emission matrix fluorescence (EEM) spectroscopy, synchronous fluorescence (SF) spectroscopy and deconvolution UV-vis (D-UV) spectroscopy were utilized to characterize AOMs to study the effects of nutrient loading on the composition change of AOMs. From results, it was revealed that the phosphorus is the limiting factor for N. palea's growth and the generation of both total organic carbon and amino acids but the nitrogen is more important for the generation of carbohydrates and proteins. EEM spectra revealed differences in the composition of extracellular organic matter and intracellular organic matter. Regardless of the nitrogen and phosphorus concentrations, aromatic proteins and soluble microbial products were the main components, but the nitrogen concentration had a significant impact on their composition. The SF spectra were used to study the AOMs for the first time and identified that the protein-like substances were the major component of AOMs, creating as a result of aromatic group condensation. The D-UV spectra showed carboxylic acid and esters were the main functional groups in the EOMs, with -OCH3, -SO2NH2, -CN, -NH2, -O- and -COCH3 functional groups substituting into benzene rings.

High-performance size exclusion chromatography with a multi-wavelength absorbance detector study on dissolved organic matter characterisation along a water distribution system

This study examined the associations between dissolved organic matter (DOM) characteristics and potential nitrification occurrence in the presence of chloramine along a drinking water distribution system. High-performance size exclusion chromatography (HPSEC) coupled with a multiple wavelength detector (200-280nm) was employed to characterise DOM by molecular weight distribution, bacterial activity was analysed using flow cytometry, and a package of simple analytical tools, such as dissolved organic carbon, absorbance at 254nm, nitrate, nitrite, ammonia and total disinfectant residual were also applied and their applicability to indicate water quality changes in distribution systems were also evaluated. Results showed that multi-wavelength HPSEC analysis was useful to provide information about DOM character while changes in molecule weight profiles at wavelengths less than 230nm were also able to be related to other water quality parameters. Correct selection of the UV wavelengths can be an important factor for providing appropriate indicators associated with different DOM compositions. DOM molecular weight in the range of 0.2-0.5kDa measured at 210nm correlated positively with oxidised nitrogen concentration (r=0.99), and the concentrations of active bacterial cells in the distribution system (r=0.85). Our study also showed that the changes of DOM character and bacterial cells were significant in those sampling points that had decreases in total disinfectant residual. HPSEC-UV measured at 210nm and flow cytometry can detect the changes of low molecular weight of DOM and bacterial levels, respectively, when nitrification occurred within the chloraminated distribution system.

Characterisation of dissolved organic matter in stormwater using high-performance size exclusion chromatography

Understanding the complexity of dissolved organic matter (DOM) in stormwater has drawn a lot of interest, since DOM from stormwater causes not only environmental impacts, but also worsens downstream aquatic quality associated with water supply and treatability. This study introduced and employed high-performance size exclusion chromatography (HPSEC) coupled with an ultraviolet-visible (UV-vis) diode array detector to assess changes in stormwater-associated DOM characteristics. Stormwater DOM was also analysed in relation to storm event characteristics, water quality and spectroscopic analysis. Statistical tools were used to determine the correlations within DOM and water quality measurements. Results showed that dissolved organic carbon (DOC) and UV absorbance at 254 nm (UV254) as conventional DOM parameters were found to be correlated well to the changes in stormwater quality during each of the three storm events studied. Both detector wavelengths (210 and 254 nm) and their ratio (A210/A254) were found to provide additional information on the physiochemical properties of stormwater-associated DOM. This study indicated that A210/A254 is an important parameter which could be used to estimate the DOM proportions of functional groups and conjugated carbon species. This study provided also an understanding of stormwater quality constituents through assessing variability and sensitivity for various parameters, and the additional information of rainfall characteristics on runoff quality data for a better understanding of parameter correlations and influences.

Catalytic ozonation of organic pollutants from bio-treated dyeing and finishing wastewater using recycled waste iron shavings as a catalyst: Removal and pathways

Catalytic ozonation of organic pollutants from actual bio-treated dyeing and finishing wastewater (BDFW) with iron shavings was investigated. Catalytic ozonation effectively removed organic pollutants at initial pH values of 7.18-7.52, and the chemical oxygen demand (COD) level decreased from 142 to 70 mg·L(-1) with a discharge limitation of 80 mg·L(-1). A total of 100% and 42% of the proteins and polysaccharides, respectively, were removed with a decrease in their contribution to the soluble COD from 76% to 41%. Among the 218 organic species detected by liquid chromatography-mass spectrometry, 58, 77, 79 and 4 species were completely removed, partially removed, increased and newly generated, respectively. Species including textile auxiliaries and dye intermediates were detected by gas chromatography-mass spectrometry. The inhibitory effect decreased from 51% to 33%, suggesting a reduction in the acute toxicity. The enhanced effect was due to hydroxyl radical (OH) oxidation, co-precipitation and oxidation by other oxidants. The proteins were removed by OH oxidation (6%), by direct ozonation, co-precipitation and oxidation by other oxidants (94%). The corresponding values for polysaccharides were 21% and 21%, respectively. In addition, the iron shavings behaved well in successive runs. These results indicated that the process was favorable for engineering applications for removal of organic pollutants from BDFW.

Spectroscopic characterization of changes of DOM deprotonation-protonation properties in water treatment processes

The deprotonation-protonation properties of dissolved organic matter (DOM) in drinking water produced at critical treatment points were quantified using absorbance spectra in combination with DOM fractionation data. Analysis of differential spectra of DOM present in inlet, settled and filtered waters from two large treatment plants and their fractions were obtained. The data demonstrated the presence of six Gaussian bands largely associated with carboxylic and phenolic DOM functionalities. Properties of the protonation-active groups of DOM in raw and treated waters were further examined based on data of potentiometric titrations at pH from 2.5 to 10. Interpretation of the differential log-transformed absorbance at wavelength 350 nm (DlnA350) based on the NICA-Donnan model showed that the normalized concentrations of low- and high-affinity protonation-active groups in residual DOMs increases as a result of water treatment. This was consistent with the results of DOM fractionation. This study demonstrates that changes of the composition and reactivity of DOM found in drinking water treatment sequences can be quantified based on the examination of their optical properties.

Are Extracted Materials Truly Representative of Original Samples? Impact of C18 Extraction on CDOM Optical and Chemical Properties

Some properties of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) can be easily measured directly on whole waters, while others require sample concentration and removal of natural salts. To increase CDOM content and eliminate salts, solid phase extraction (SPE) is often employed. Biases following extraction and elution are inevitable, thus raising the question of how truly representative the extracted material is of the original. In this context, we investigated the wavelength dependence of extraction efficiency for C18 cartridges with respect to CDOM optical properties using samples obtained from the Middle Atlantic Bight (MAB) and the Equatorial Atlantic Ocean (EAO). Further, we compared the optical changes of C18 extracts and the corresponding whole water following chemical reduction with sodium borohydride (NaBH₄). C18 cartridges preferentially extracted long-wavelength absorbing/emitting material for samples impacted by riverine input. Extraction efficiency overall decreased with offshore distance away from riverine input. Spectral slopes of C18-OM samples were also almost always lower than those of their corresponding CDOM samples supporting the preferential extraction of higher molecular weight absorbing material. The wavelength dependence of the optical properties (absorption, fluorescence emission, and quantum yield) of the original water samples and their corresponding extracted material were very similar. C18 extracts and corresponding water samples further exhibited comparable optical changes following NaBH₄ reduction, thus suggesting a similarity in nature (structure) of the optically active extracted material, independent of geographical locale. Altogether, these data suggested a strong similarity between C18 extracts and corresponding whole waters, thus indicating that extracts are representative of the CDOM content of original waters.

The role of autoinducer-2 in aerobic granulation using alternating feed loadings strategy

Quorum sensing (QS) plays an important role in aerobic granulation while how QS system regulates the formation of aerobic granules needs further discussion. This study cultivated activated sludge in two identical sequencing batch reactors (R1 and R2) at different influent organic loading rate (OLR) strategies: R1 was operated using constant OLR (around 8.0kg/m(3)d), while R2 was operated at alternating OLR (4.0-17.0kg/m(3)d). Microbial aggregates appeared in R2 on day 19, while the morphology of sludge in R1 changed little compared with the initial sludge. The concentration of autoinducer-2 (AI-2) in R2 showed an ascending trend, along with the increase of cell adhesiveness. The total extracellular polymeric substances (EPS) amount and large molecular weight EPS of R2 rose steadily, which was different from R1. Some bacteria able to self-aggregate and promote EPS secretion were exclusive in R2. A mechanism about aerobic granulation at alternating OLR was proposed.

Comparison of Cr(VI) removal by activated sludge and dissolved organic matter (DOM): importance of UV light

Removal of toxic Cr(VI) by activated sludge and DOM derived from activated sludge was investigated in this study. A rapid increase in TOC concentration from 50.93 to 127.40 mg L(-1) is observed during the Cr(VI) removal process by activated sludge in the pH range of 2-9. Removal efficiencies of Cr(VI) by either activated sludge or DOM greatly decreased with the increasing initial pH. Kinetics of Cr(VI) removal by activated sludge indicate that both biosorption and bioreduction are involved in the Cr(VI) removal. Cr(VI) removal by DOM is slow in dark, but it is greatly enhanced when UV light is applied. The first-order constant increases from 0.0033 (in dark) to 0.079 min(-1) (UV illumination) at pH 2.0 and 1068 mg L(-1) DOM. The enhancement of Cr(VI) reduction is due to the generation of the reactive intermediates such as O2(●-) and DOM* as DOM absorbed light energy, which plays important roles in the reduction of Cr(VI).

A critical review on characterization strategies of organic matter for wastewater and water treatment processes

The presence of organic matter (OM) in raw wastewater, treated wastewater effluents, and natural water samples has been known to cause many problems in wastewater treatment and water reclamation processes, such as treatability, membrane fouling, and the formation of potentially toxic by-products during wastewater treatment. This paper summarizes the current knowledge on the methods for characterization and quantification of OM in water samples in relation to wastewater and water treatment processes including: (i) characterization based on the biodegradability; (ii) characterization based on particle size distribution; (iii) fractionation based on the hydrophilic/hydrophobic properties; (iv) characterization based on the molecular weight (MW) size distribution; and (v) characterization based on fluorescence excitation emission matrix. In addition, the advantages, disadvantages and applications of these methods are discussed in detail. The establishment of correlations among biodegradability, hydrophobic/hydrophilic fractions, MW size distribution of OM, membrane fouling and formation of toxic by-products potential is highly recommended for further studies.

Chromatographic methods for the isolation, separation and characterisation of dissolved organic matter

This review presents an overview of the separation techniques applied to the complex challenge of dissolved organic matter characterisation. The review discusses methods for isolation of dissolved organic matter from natural waters, and the range of separation techniques used to further fractionate this complex material. The review covers both liquid and gas chromatographic techniques, in their various modes, and electrophoretic based approaches. For each, the challenges that the separation and fractionation of such an immensely complex sample poses is critically reviewed.

Spectrophotometric characterization of dissolved organic matter in a rural watershed: the Madon River (N-E France)

In the last 20 years, increasing dissolved organic carbon (DOC) concentrations have been observed in several rivers and lakes in Europe. This increase has reduced the quality of the aquatic environment. In this study, UV-vis spectroscopy and synchronous fluorescence spectroscopy with a difference of 50 nm between the excitation and emission (SF50) were used to characterize the DOC in a rural river (Madon River). The specific absorbance index at 254 nm (SUVA254) which is related to the aromaticity of DOC was extracted from UV-vis spectra, whose maximum of the second derivative (occurring near 225 nm) is related to nitrates. SF50 spectra which are characterized by well-defined peaks indicated large spatial and temporal variations. Two methods were used to analyze and compare these spectra. The first method was based on the decomposition of the SF50 spectra into four Gauss functions: B1 (related to tryptophan-like fluorescence), B2 and B3 (related to humic substances), and B4 (related to chlorophyll-like substances). The second method was principal components analysis (PCA), which results yielded three principal components that accounted for 95% of the variance. Although PCA enables the consideration of the spectra without making assumptions regarding the number of fluorophores, the results from the decomposition in Gauss function were easier to interpret.

Effects of standard humic materials on relative bioavailability of NDL-PCBs in juvenile swine

Young children with their hand-to-mouth activity may be exposed to contaminated soils. However few studies assessing exposure of organic compounds sequestrated in soil were realized. The present study explores the impact of different organic matters on retention of NDL-PCBs during digestive processes using commercial humic substances in a close digestive model of children: the piglet. Six artificial soils were used. One standard soil, devoid of organic matter, and five amended versions of this standard soil with either fulvic acid, humic acid, Sphagnum peat, activated carbon or a mix of Sphagnum peat and activated carbon (95∶5) (SPAC) were prepared. In order to compare the different treatments, we use spiked oil and negative control animals. Forty male piglets were randomly distributed in 7 contaminated and one control groups (n = 5 for each group). During 10 days, the piglets were fed artificial soil or a corn oil spiked with 19,200 ng of Aroclor 1254 per g of dry matter (6,000 ng.g⁻¹ of NDL-PCBs) to achieve an exposure dose of 1,200 ng NDL-PCBs.Kg⁻¹ of body weight per day. NDL-PCBs in adipose tissue were analyzed by GC-MS. Fulvic acid reduced slightly the bioavailability of NDL-PCBs compared to oil. Humic acid and Sphagnum peat reduced it significantly higher whereas activated carbon reduced the most. Piglets exposed to soil containing both activated carbon and Shagnum peat exhibited a lower reduction than soil with only activated carbon. Therefore, treatment groups are ordered by decreasing value of relative bioavailability as following: oil ≥ fulvic acid>Sphagnum peat ≥ Sphagnum peat and activated carbon ≥ Humic acid>>activated carbon. This suggests competition between Sphagnum peat and activated carbon. The present study highlights that quality of organic matter does have a significant effect on bioavailability of sequestrated organic compounds.

The importance of charge-transfer interactions in determining chromophoric dissolved organic matter (CDOM) optical and photochemical properties

Absorption of sunlight by chromophoric dissolved natural organic matter (CDOM) is environmentally significant because it controls photic zone depth and causes photochemistry that affects elemental cycling and contaminant fate. Both the optics (absorbance and fluorescence) and photochemistry of CDOM display unusual properties that cannot easily be ascribed to a superposition of individual chromophores. These include (i) broad, unstructured absorbance that decreases monotonically well into the visible and near IR, (ii) fluorescence emission spectra that all fall into a single envelope regardless of the excitation wavelength, and (iii) photobleaching and photochemical quantum yields that decrease monotonically with increasing wavelength. In contrast to a simple superposition model, these phenomena and others can be reasonably well explained by a physical model in which charge-transfer interactions between electron donating and accepting chromophores within the CDOM control the optical and photophysical properties. This review summarizes current understanding of the processes underlying CDOM photophysics and photochemistry as well as their physical basis.

Understanding effects of water characteristics on natural organic matter treatability by PACl and a novel PACl-chitosan coagulants

In this study, we investigated the relationship between water characteristics and removal of natural organic matter (NOM) using polyaluminium chloride (PACl) and a newly developed coagulant obtained by hybridising PACl with chitosan (PACl-chitosan) for two different types of water. Using UV-visible spectroscopy analysis, we showed that PACl-chitosan is more effective than PACl for treating water samples that contain higher levels of activated polyhydroxyaromatic moieties. As a result, a lower level of total trihalomethanes formation potential (THMFP) was detected for synthetic water treated with PACl-chitosan coagulant compared to water treated with PACl only. In contrast, no difference was observed for the total THMFP that were formed following coagulation with either coagulant, for water sample containing the same level of organic carbon concentration, but lower levels of polyhydroxyaromatic moieties. Our work shows how the complex characteristics and interactions of organic matter with coagulant component can affect the outcome of the treatment process, and in this case, enhance the treatment. The use of PACl-chitosan was also shown to produce larger floc for both water samples; this again, can lead to better removal.

Disinfection by-products formation and precursors transformation during chlorination and chloramination of highly-polluted source water: significance of ammonia

Many studies have demonstrated the different trends of disinfection by-products (DBPs) formation between chlorination and chloramination. However, the reactions between precursors and disinfectants are widely assumed to be "black box" and the reasons for abovementioned difference are not well illustrated. This study focused on source water with high levels of natural organic matter (NOM) and bromide, and compared the transformation of NOM specific characteristics and the ratios of specific DBPs as an equivalent of chlorine to total organic halogen (TOX) among three disinfection scenarios of chlorination, chloramination and chlorine-chloramine sequential treatment (Cl2-NH2Cl process). A three-reaction-phrases model was proposed thereafter to illustrate the major reactions involved in, i.e., stage-I: rapid consumption of fast reactive sites (DOC1), which transformed to slow reactive sites (DOC2) and measured DBPs, i.e., trihalomethanes, haloacetic acids, etc; stage-II: oxidation and/or halogenation of DOC2 into unknown TOX (UTOX) intermediates; stage-III: oxidation of UTOX intermediates into measured DBPs. The effect of ammonia was also quantified. Ammonia is observed to inhibit the formation of measured DBPs by 68-92%, 94-99%, and 92-95% of that in chlorination in Stage-I, II, and III, respectively, and the formation of UTOX is reduced by 2-80%, 60-94%, and 82-93% accordingly. These effects lead to the steady accumulation of DBPs intermediates such as UTOX, and to the elevated UTOX/TOX during chloramination and Cl2-NH2Cl process thereafter. The results illustrate the mechanism of ammonia participating in DBPs formation, and are valuable to fill in the gap between the transformation of precursors and the formation of different DBPs.