Optimization of method for detecting and characterizing NOM by HPLC-size exclusion chromatography with UV and on-line DOC detection

Quantification of high molecular weight organic carbon concentrations with LC-OCD and PHMOC for biological stability investigation of drinking water produced from surface water

The presence of aquatic biopolymeric organic carbon of high (> 10 - 20 kDa) molecular weight (high-MW OC) in drinking water produced from surface water affects its biological stability which may cause regrowth in disinfectant-free distribution. This study compares two analytical methods for determining the concentration of aquatic high-MW OC, namely LC-OCD (liquid chromatography - organic carbon detection) and PHMOC (particulate and colloidal high-molecular weight OC). LC-OCD entails prefiltration of the water sample, chromatographical separation of the relevant biopolymer (BP) OC-fraction, and in-line OC detection. PHMOC is based on the total OC content of the concentrate obtained after 30 kDa crossflow ultrafiltration of the water sample. LC-OCD BP and PHMOC showed a good linear correlation (R2 0.87) for a suite of treated surface water matrices (except raw water) in the 10 - 200 µg/L concentration range, with PHMOC values being 10% - 30% higher than the corresponding LC-OCD BP value, without a clear impact of other water matrix constituents. The indicative yields and selectivities of both methods for indigenous high-MW OC obtained from the PHMOC concentrate were high (≥ 70% - 88%) but not fully complete, which may explain the observed higher PHMOC values and scatter in the PHMOC - LC-OCD BP correlation. LC-OCD BP and PHMOC displayed similar values and trends across the different seasons and treatment stages, with treated ground water and infiltrated water having the lowest (< 10 µg/L) values. Regrowth (as Aeromonas) levels in disinfectant-free distribution networks corresponded with the high-MW OC concentration in the treated drinking water. Overall, the two methods equivalently quantify the concentration of aquatic high-MW OC. Both methods are suitable for use in biological stability studies. The small sample volume renders LC-OCD more practical, whereas the PHMOC method enables further experimentation and characterization of the high-MW OC fraction.

Transformative characteristics of aquatic and soil organic matter in a constructed wetland consisting of Acorus, Nuphar, and Typha ponds

This study investigated the transformative characteristics of dissolved organic matter (DOM) within constructed wetlands (CWs) and elucidated the distinct interplay between aquatic DOM and soil organic matter (SOM) during different treatment stages. Through comprehensive analyses, including water quality assessments, molecular weight distribution, fluorescence spectrometry, and molecular structure analysis, our investigation revealed profound transformations in aquatic DOM characteristics facilitated by CWs. Notably, the significant increase in dissolved organic carbon (DOC) concentrations within the Typha pond underscored the pivotal role of anaerobic decomposition in organic matter accumulation. Structural analysis indicated a transition toward lipid- and protein-based substances, suggesting robust microbial degradation of aromatic DOMs. Considerable differences between aquatic DOM and SOM were observed, with SOM exhibiting a lower molecular weight and a richer array of oxygen-containing functional groups of organic substances, indicative of soil adsorption processes. This study highlights the transformation of DOM in CWs as a complex interaction between autochthonous and allochthonous sources, in which the soil adsorption of specific organic fractions notably influences the CW ecosystem. Our findings emphasize the capacity of CW to enhance water quality through natural remediation processes and provide valuable insights into optimizing CW design and management for improved wastewater treatment and ecological sustainability.

Thorough Validation of Optimized Size Exclusion Chromatography-Total Organic Carbon Analysis for Natural Organic Matter in Fresh Waters

Size exclusion chromatography with total organic carbon detection (HPSEC-TOC) is a widely employed technique for characterizing aquatic natural organic matter (NOM) into high, medium, and low molecular weight fractions. This study validates the suitability of HPSEC-TOC for a simplified yet efficient routine analysis of freshwater and its application within drinking water treatment plants. The investigation highlights key procedural considerations for optimal results and shows the importance of sample preservation by refrigeration with a maximum storage duration of two weeks. Prior to analysis, the removal of inorganic carbon is essential, which is achieved without altering the NOM composition through sample acidification to pH 6 and subsequent N2-purging. The chromatographic separation employs a preparative TSK HW-50S column to achieve a limit of detection of 19.0 µgC dm-3 with an injection volume of 1350 mm-3. The method demonstrates linearity up to 10,000 µgC dm-3. Precision, trueness and recovery assessments are conducted using certified reference materials, model compounds, and real water samples. The relative measurement uncertainty in routine analysis ranges from 3.22% to 5.17%, while the measurement uncertainty on the bias is 8.73%. Overall, the HPSEC-TOC represents a reliable tool for NOM fractions analysis in both treated and untreated ground and surface water.

Unraveling the evolution of dissolved organic matter in full-scale A/A/O wastewater treatment process using size exclusion chromatography with PARAFAC and nonnegative matrix factorization analysis

Changes in spectral features and molecular weight (MW) of dissolved organic matter (DOM) along the A/A/O processes in eight full-scale wastewater treatment plants (WWTPs) were characterized using size exclusion chromatography with a diode array detector, a fluorescence detector and an organic carbon detector in tandem (SEC-DAD-FLD-OCD) as well as bulk water quality parameters. The parallel factor (PARAFAC) and the nonnegative matrix factorization (NMF) analyses have been effectively applied to the postprocessing of SEC-FLD fingerprints and SEC-OCD chromatograms, respectively. Individual SEC-FLD-PARAFAC or SEC-OCD-NMF components may span a broad range of MW, indicating that these SEC fractions within the same component were cognate and varied coherently across the dataset samples. The SEC-FLD-PARAFAC modeling and SEC-OCD-NMF analysis have clearly and concisely presented that the dramatic decreases of dissolved organic carbon, UV absorbance at 254 nm and protein-like fluorescence at Ex280/Em350 nm in the anaerobic process were primarily associated with the degradation of the large MW proteinaceous and polysaccharide-like biopolymers. It has also revealed that fluorescence of humic acid-like fractions increased significantly during the anaerobic process, but fluorescence of fulvic acid-like and humic substances' building blocks decreased slightly. Laboratory experiments further confirmed the presence of the humification process in anaerobic processes, and the formation of humic acid-like fluorophores may be associated with carbohydrate metabolism. The combination of SEC-FLD-PARAFAC and SEC-OCD-NMF helped to establish the links between changes in bulk water quality parameters and the evolution of SEC MW fractions, which provides a more in-depth insight into wastewater DOM treatability and enables the optimization of wastewater treatment processes.

An autopsy study of hollow fiber and multibore ultrafiltration membranes from a pilot-scale ultra high-recovery filtration system for surface water treatment

The organic fouling characteristics of hollow fiber ultrafiltration (HFUF) and multibore ultrafiltration (MBUF) membranes from long-term ultrafiltration (UF) membrane systems were systemically investigated in this study. The objective was to obtain insights into the fouling behavior of dissolved organic matter (DOM) in a pilot-scale ultra-high-recovery membrane filtration system (p-UHMS) used for surface water treatment. The pilot system consisted of a series of two different UF membranes (1st stage: polyvinylidene fluoride (PVDF) HFUF and 2nd stage: polyethersulfone (PES) MBUF). It was designed to feed the HFUF concentrate to the MBUF membranes to achieve ≥99.5 % total water recovery for surface water treatment, as these advances might enhance the production efficiencies of drinking water. The experimental results confirmed that hydrophobic DOM controlled the formation of HFUF membrane organic fouling, whereas hydrophilic DOM, including polysaccharide-like and protein-like matter, promoted MBUF membrane fouling. These opposing trends were attributed to the hydrophilic characteristics of the MBUF membrane surfaces (contact angle: PVDF = 90-130° and PES ≤ 80°), which reduced the hydrophobic interactions between the UF membrane surfaces and foulants. The performance declines of the MBUF membrane due to fouling layer formation was considerably severer than those of the HFUF membrane, decreasing total permeate water in the p-UHMS. Moreover, the quantity of the desorbed MBUF membrane foulants via 0.1 N NaOH was roughly 7.2 times larger than that of the desorbed HFUF membrane foulants through 0.1 N NaOH, indicating that alkaline-based cleaning agent could much more efficiently recover the performance of the fouled MBUF membranes. Hence, adequate cleaning strategies using alkaline-based agent for the MBUF membrane appeared to be essential for preventing the performance deterioration of the p-UHMS.

Formation of Nano- and Microplastics and Dissolved Chemicals During Photodegradation of Polyester Base Fabrics with Polyurethane Coating

Polyurethane (PU) synthetic leathers possess an intricate plastic composition, including polyester (PET) base fabrics and upper PU resin, but the release of fragments from the complexes is unclear. Therefore, we investigated the photodegradation trends of PET base fabrics with PU coating (PET-U) as a representative of composite plastics. Attention was paid to the comparison of the photoaging process of PET-U with that of pure PET base fabric (PET-P). To reveal the potential for chain scission, physical and chemical changes (e.g., surface morphology, molecular weight, and crystallinity) of the two fabrics were explored. The generation of microplastic fibers (MPFs) and microplastic particles (MPPs) was distinguished. Compared with PET-P, PET-U showed a similar but delayed trend in various characteristics and debris release rate as the photoaging time prolonged. Even so, after 360 h of illumination, the generated number of MPs (including MPFs and MPPs) rose considerably to 9.32 × 10⁷ MPs/g, and the amount of released nanoplastics (NPs) increased to 2.70 × 10¹¹ NPs/g from PET-U. The suppression of MP formation from PET-U was potentially directed by the physical shielding of the upper PU layer and the dropped MPs, which resisted the photochemical radical effect. The components of dissolved organic matter derived from plastics (P-DOM) were separated by molecular weight using a size-exclusion chromatography-diode array detector-organic carbon detector/organic nitrogen detector (SEC-DAD-OCD/OND), and the results showed that a larger amount of carbon- and nitrogen-containing chemical substances were generated in PET-U, accompanied by more aromatic and fluorescent compounds. The results provided theoretical bases and insights for future research on the risks of plastic debris from PU synthetic leathers on aquatic organisms and indicated feasible directions for exploring combined pollution studies of plastics.

Key factors in the adsorption of natural organic matter to metal (hydr)oxides: Fractionation and conformational change

Adsorption of natural organic matter (NOM) to mineral surfaces is an important process determining the environmental fate and biogeochemical cycling of many elements. Natural organic matter consists of a heterogeneous mixture of soft and flexible organic molecules. Upon adsorption, size fractionation may occur, as well as changes in molecular conformation. Although very important, these phenomena have been omitted in existing adsorption models. Filling this gap, a novel framework for NOM adsorption to metal (hydr)oxides is presented. Humic acid (HA) was used as an analog for studying experimentally the NOM adsorption to goethite and its size fractionation as a function of pH, ionic strength, and surface loading. Size fractionation was evaluated for adsorption isotherms collected at pH 4 and 6, showing HA molecules of low molar mass were preferentially adsorbed. This phenomenon was incorporated into the new model. Consistent description of the HA adsorption data over the entire range of pH (3-11), ionic strength (2-100 mM), and surface loading (0.1-3 mg m^-2) indicated that the spatial distribution of HA molecules adsorbed in the interface is a trade-off between maximizing the interaction of the HA ligands with the oxide surface and minimizing the electrostatic repulsion between HA particles as a result of interfacial crowding. Our advanced consistent framework is able to quantify changes in molar mass and molecular conformation, thereby significantly contributing to an improved understanding of the competitive power of HA for interacting on oxides with other adsorbed small organic acids as well as environmentally important oxyanions, such as phosphate, arsenate, and others.

Microheterogeneous Triplet Oxidation of Hydrophobic Organic Contaminants in Dissolved Black Carbon Solutions under Simulated Solar Irradiation

Dissolved black carbon (DBC) is proven to accelerate the triplet-mediated photodegradation of hydrophobic organic contaminants (HOCs). However, its photosensitization mechanisms are not clear. In this study, five HOCs including 2,4,6-trimethylphenol, N,N-dimethylaniline, 17β-estradiol, 17α-ethinylestradiol, and bisphenol A were selected as model compounds to explore the triplet-mediated phototransformation of HOCs in illuminated DBC solutions. All five HOCs presented high organic carbon-water partition coefficient (K_OC) values in DBC solutions, indicating the strong sorption capacity of DBC for HOCs. When reaching sorption equilibrium, the apparent pseudo-first-order rate constants of HOCs vs log[DBC] were well fitted with a sorption-enhanced phototransformation model (R² > 0.98). Using the sorption-enhanced phototransformation model, the degradation rates of HOCs determined at intra-DBC (k_DBC,HOCs^') were 1-2 orders of magnitude higher than those observed in aqueous bulk solution (k_HOCs^aq). Moreover, typical triplet quenchers (2,4,6-trimethylphenol and oxygen) exhibited a microheterogeneous quenching effect on the triplet-mediated photodegradation of 17β-estradiol. Therefore, our results suggested that HOCs underwent a microheterogeneous photooxidative degradation process in DBC solutions. Furthermore, a sorption-enhanced phototransformation mechanism was proposed to elucidate the microheterogeneous photooxidative behavior of HOCs in DBC solutions. This study provides new insights into the fate and transport of HOCs in aquatic environments.

Enhanced removal of humic substances in effluent organic matter from a leachate treatment system via biological upgradation of molecular structure

Biological upgradation (BU) process was proposed, with the goal of converting the molecular structure, for improving the coagulation effect on humic substances (HS) in effluent organic matter from the membrane bioreactor of a leachate treatment system. Enhancement of coagulation effect was observed with the improvement of chemical oxygen demand and HS removal efficiency from 45.5% and 56.5% to 80.0% and 92.6% (Fe dosage was 400 mg·L^-1), respectively, which was approximately 30-40% higher than the other available researches. Variations in molecular weight (MW) and carboxyl contents of fulvic acid (FA) and humic acid (HA) were analysed by size exclusion chromatography coupled with dissolved organic carbon detection, potentiometric titration and Fourier transform infrared spectroscopy. The obtained results indicated that BU process led to the growth of MW of HS, of which the larger MW (1650 Da) FA and HA raised from 19.07 and 0.34 mgC·L^-1 to 71.67 and 1.58 mgC·L^-1, respectively, as well as increases in the carboxyl contents of FA and HA from 6.70 and 6.28 meq·gC^-1 to 11.84 and 8.71 meq·gC^-1, respectively. Because of this, a stronger binding effect between Fe and HS might be formed that improved the coagulation effect.

Novel insights into the interaction reactive components and synergistic fouling mechanisms of ultrafiltration by natural organic matter fractions and kaolin

The mechanisms governing interactions among various natural organic matter (NOM) fractions and the subsequently impact on ultrafiltration process have not been systematically studied. In this work, bovine serum albumin (BSA), humic acid (HA), sodium alginate (SA) were applied as model NOM to explore the influence of the interactions among NOM on ultrafiltration process. Results indicated that tryptophan-like fluorescence fraction was the dominant reaction fraction of HA to react with SA and BSA. Different interactions among model NOM not only changed the interception order of fluorescence fractions by ultrafiltration from fulvic acid-like, humic-like and tryptophan-like in BSA/HA mixture to tryptophan-like, humic-like and fulvic acid-like in BSA/HA/SA/kaolin mixture, but also remarkably influence the membrane fouling behavior. In BSA/HA mixture, new-generated aggregates with molecular weight (MW) of 10 kDa could not pass though ultrafiltration membrane and mainly contributed to chemical reversible fouling. In BSA/HA/SA mixture, SA simultaneously reacted with BSA and HA to generate aggregates with larger MW which could be washed down by physical cleaning. In BSA/HA/SA/kaolin mixture, the aggregates with MW of 10 kDa and chemical reversible fouling were disappeared due to the adsorption role of kaolin. These findings could further improve our understanding regarding membrane fouling mechanisms of raw water with different components.

Molecular investigation on changing behaviors of natural organic matter by coagulation with non-targeting screen using high-resolution mass spectrometry

Natural organic matter (NOM) can tremendously influence the purification efficiency of the drinking water treatment process. Coagulation was the first and primary process of NOM removal in the drinking water treatment process. The interaction between coagulants and NOM molecules remains unclear. Three typical coagulants (Al₁₃, FeCl_3, and AlCl₃) were used to investigate the effects on NOM removal. The measurement of NOM was conducted using 15 T Electrospray Ionization coupled Fourier-Transform-Ion Cyclotron Resonance Mass Spectrometry (ESI-FT-ICR MS). The coagulation process altered the mass peak numbers as well as relative intensity of the peaks which were positively correlated with TOC value. The lignin-like compound was the most abundant moiety in raw water. Al-based coagulants remove more unsaturated larger compounds (lower KMD and higher carbon number). Al₁₃ remove the unsaturated hydrocarbons preferably. FeCl₃ is more reactive with NOM molecules and removes more fully saturated compounds. These findings revealed the coagulation removal mechanism of NOM with different structural characteristics and advise the practical use of coagulants for various raw water with different NOM characteristics.

Characterizing dissolved organic matter in aquatic environments by size exclusion chromatography coupled with multiple detectors

Size exclusion chromatography (SEC) is one of the most commonly used techniques to detect the molecular weight (MW) of dissolved organic matter (DOM) in aquatic environments. The significant improvement and focus of this method have been the application of multiple detectors, which contribute to providing fundamental physicochemical properties of various MW fractions. This study has coupled SEC with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon, and dissolved organic nitrogen of different MW fractions. The detection limits for the organic carbon and nitrogen detectors were 0.20 μg C L^-1 and 0.14 μg N L^-1, respectively. Furthermore, we gave an interpretation of the nature and evolution of DOM in surface water based on the comparison and analyses of the combined chromatogram obtained from multiple detectors. Fractions assigned as hydrophobic humic-like substances, hydrophilic humic-like substances, low-MW microbial extracellular metabolites and low-MW hydrophobic protein-like substances were first established in this study and attributed to the presence of a fluorescence detector. We believe that the developed method provides in-depth knowledge of the structure and composition of DOM and could be used as a potential analytical tool in environmental organic chemistry, humus chemistry and supramolecular chemistry.

Composition Wheels: Visualizing dissolved organic matter using common composition metrics across a variety of Canadian ecozones

Dissolved organic matter (DOM) is a ubiquitous component of aquatic systems, impacting aquatic health and drinking water quality. These impacts depend on the mixture of organic molecules that comprise DOM. Changing climates are altering both the amount and character of DOM being transported from the terrestrial system into adjacent surface waters, yet DOM composition is not monitored as often as overall concentration. Many DOM characterization methods exist, confounding comparison of DOM composition across different studies. The objective of this research is to determine which parameters in a suite of relatively simple and common DOM characterization techniques explain the most variability in DOM composition from surface and groundwater sites. Further, we create a simple visualization tool to easily compare compositional differences in DOM. A large number of water samples (n = 250) was analyzed from six Canadian ecozones for DOM concentration, ultraviolet-visible light absorbance, molecular size, and elemental ratios. Principal component analyses was used to identify quasi-independent DOM compositional parameters that explained the highest variability in the dataset: spectral slope, specific-UV absorbance at 255nm, humic substances fraction, and dissolved organic carbon to dissolved organic nitrogen ratio. A ‘Composition Wheel’ was created by plotting these four parameters as a polygon. Our results find similarities in DOM composition irrespective of site differences in vegetation and climate. Further, two main end-member Composition Wheel shapes were revealed that correspond to DOM in organic-rich groundwaters and DOM influenced by photodegradation. The Composition Wheel approach uses easily visualized differences in polygon shape to quantify how DOM evolves by natural processes along the aquatic continuum and to track sources and degradation of DOM.

Gold-Carbon Nanocomposites for Environmental Contaminant Sensing

The environmental crisis, due to the rapid growth of the world population and globalisation, is a serious concern of this century. Nanoscience and nanotechnology play an important role in addressing a wide range of environmental issues with innovative and successful solutions. Identification and control of emerging chemical contaminants have received substantial interest in recent years. As a result, there is a need for reliable and rapid analytical tools capable of performing sample analysis with high sensitivity, broad selectivity, desired stability, and minimal sample handling for the detection, degradation, and removal of hazardous contaminants. In this review, various gold–carbon nanocomposites-based sensors/biosensors that have been developed thus far are explored. The electrochemical platforms, synthesis, diverse applications, and effective monitoring of environmental pollutants are investigated comparatively.

Screening of Marine Bioactive Antimicrobial Compounds for Plant Pathogens

Plant diseases have been threatening food production. Controlling plant pathogens has become an important strategy to ensure food security. Although chemical control is an effective disease control strategy, its application is limited by many problems, such as environmental impact and pathogen resistance. In order to overcome these problems, it is necessary to develop more chemical reagents with new functional mechanisms. Due to their special living environment, marine organisms have produced a variety of bioactive compounds with novel structures, which have the potential to develop new fungicides. In the past two decades, screening marine bioactive compounds to inhibit plant pathogens has been a hot topic. In this review, we summarize the screening methods of marine active substances from plant pathogens, the identification of marine active substances from different sources, and the structure and antibacterial mechanism of marine active natural products. Finally, the application prospect of marine bioactive substances in plant disease control was prospected.

Relationships among Permeability, Membrane Roughness, and Eukaryote Inhabitation during Submerged Gravity-Driven Membrane (GDM) Filtration

Gravity-driven membrane (GDM) filtration is one of the promising technologies for decentralized water treatment systems due to its low cost, simple operation, and convenient maintenance. The objective of this study was to evaluate the permeability of submerged GDM filtration with three different membranes, i.e., polyethersulfone and polyvinylidene difluoride ultrafiltration (PES-UF and PVDF-UF) and polytetrafluoroethylene microfiltration membrane (PTFE-MF). The GDM system was operated using lake water for about one year. The determined average permeability values were high for PVDF-UF (192.9 L/m2/h/bar (LMH/bar)) and PTFE-MF (80.6 LMH/bar) and relatively lower for PES-UF (46.1 LMH/bar). The observed higher permeability for PVDF-UF and PTFE-MF was thought to be related to the rougher surface of these two membranes compared to PES-UF. The fouling layers of PVDF-UF and PTFE-MF were characterized by high biomass and the presence of a number of nematodes, while PES-UF showed a thin fouling layer with no nematode. The relatively high and fluctuated permeability of PVDF-UF and PTFE-MF could thus be attributed to the high biological activity of nematodes making the fouling layer more loose and porous. This was supported by a good linear relationship among the permeability, biomass concentration, and the number of nematodes in the fouling layers. These results provide important insights into membrane selection as a critical factor affecting the flux performance of the GDM filtration system for a decentralized drinking water supply.

Effects of fulvic acids on the electrochemical reactions and mass transfer properties of organic cation toluidine blue: Results of measurements by the method of rotating ring-disc electrode

This study examined effects of aquatic and soil natural organic matter (NOM) exemplified by standard Suwannee River fulvic acid (SRFA) and Pahokee Peat fulvic acid (PPFA), respectively, on the electrochemical (EC) reactivity and mass transfer properties of the cationic organic probe toluidine blue (TB) that forms complexes with NOM. EC measurements that were carried out using the method of rotating ring-disc electrode (RRDE) showed that for disc potentials below -0.4 V vs. the standard Ag/AgCl reference electrode, TB molecules undergo EC reduction accompanied by the formation of EC-active products that undergo oxidation at the ring electrode. EC reactions of TB in the range of potentials -0.2 to -0.4 V were determined to involve free TB⁺ cations and TB species adsorbed on the electrode surface. The EC reduction of TB species at the disc potentials < -0.4 V was controlled by the mass transfer of the free TB⁺ cations and TB/NOM complexes to the electrode surface. Formation of TB/NOM complexes caused the mass transfer-controlled TB currents to undergo a consistent decrease. The observed changes were correlated with the extent of TB/NOM complexation and decreases of the diffusion coefficients of TB/NOM complexes that have higher molecular weights (MW) than the free cations. Properties of the intermediates formed upon the reduction of TB⁺ cations were also affected by NOM. These results demonstrate that RRDE measurements of EC reactions of TB or possibly other EC active probes allow probing the complexation of EC-active organic species with NOM and mass transfer properties of NOM complexes and ultimately NOM itself.

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.

Insight into Fe(II)/UV/chlorine pretreatment for reducing ultrafiltration (UF) membrane fouling: Effects of different natural organic fractions and comparison with coagulation

Fe(II)/UV/chlorine was promoted as a pretreatment strategy for UF membrane to mitigate membrane fouling induced from different organic fractions. This treatment could be an emerging alternative prior to UF process attributed to the coupled role of oxidation and coagulation. To obtain a comprehensive understanding of fouling reduction, the influence of Fe(II)/UV/chlorine process on the characteristics of various feed solutions was inspected, including humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA) and their mixture (HSB). The results suggested that Fe(II)/UV/chlorine process exhibited notable performance on membrane fouling control compared to Fe(II) coagulation alone. With the UV exposure of 720 mJ/cm², the certain dose of Fe(II) and chlorine (15 μM and 2 mg/L) effectively prevented the rapid development of fouling caused by the single organic fractions and their mixture. And the increased dosage promoted the performance of membrane fouling mitigation. The reduction of organic loadings and characteristics change of feed water took the main responsibility for the fouling alleviation. The properties of membrane fouling and their correlation with feed water qualities were analyzed. The results and insight analysis were supposed to evaluate and predict the effectiveness of fouling control when the feed solutions were pretreated by Fe(II)/UV/chlorine process according to various compositions and characteristics of the organic fractions.

An evaluation of measurement techniques for algal-derived organic nitrogen

Algal-derived organic matter (AOM) from algal blooms in water supply systems contains dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) among other constituents. The DON and DOC are disinfection by-product (DBP) precursor compounds, and must be well characterised to facilitate effective removal, thus minimising DBP formation during disinfection. While DOC character has been studied extensively, DON analysis suffers from inaccuracies due to sample pre-treatment and instrument sensitivities. A liquid chromatography method that combines size exclusion chromatography with highly sensitive organic carbon and nitrogen detectors (LC-OCND) has been widely adopted for DOC analysis; however, its potential for application for DON charactersation has been suggested as a viable alternative to existing DON characterisation techniquesnot been assessed despite its potential. Hence, the aim was to compare the effectiveness of conventional total dissolved N-dissolved inorganic N (TN-DIN), and LC-OCND methods for analysing DON in AOM. A suite of N-containing model compounds representative of DON and AOM extracted from Chlorella vulgaris CS-42/7 and Microcystis aeruginosa CS-555/1 were used to evaluate the techniques. The DON of both model compounds and AOM was first analysed using the conventional method and, then, via LC-OCND. It was observed that LC-OCND had a better precision for DON when TN contained more DIN. LC-OCND provided direct quantitative measurements for bulk and fractionated DON and DIN, with little interference caused by DIN. Additionally, LC-OCND provided information on MW distribution and protein content of the AOM. For example, LC-OCND results showed that M. aeruginosa AOM contained more HMW material than C. vulgaris AOM. However, as LC-OCND uses UV oxidation, it could not completely oxidise complex aromatic structures, and thus had a lower recovery for HMW model compounds and algal DON in comparison to the conventional method that used high temperature catalytic oxidation. Overall, it is advised that a combination of LC-OCND and TN analysis be used to provide a more detailed characterisation of N-containing AOM and other similar HMW aquatic NOM samples.

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.

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.

Rapid and Effective Isolation of Dissolved Organic Matter Using Solid-Phase Extraction Cartridges Packed with Amberlite XAD 8/4 Resins

Using the conventional XAD 8/4 method with general columns to isolate dissolved organic matter (DOM) is extremely time-consuming and labor-intensive. This study presents a rapid and effective method using solid-phase extraction (SPE) cartridges packed with XAD 8/4 resins for isolating various DOMs. The relative fraction (percentage hydrophobic, transphilic, and hydrophilic) of the various DOMs processed by both methods showed similar values. Moreover, changes in the molecular weight distribution of effluent from XAD 8/4 resins processed by both methods showed the same ultraviolet (UV) and fluorescence absorbance pattern s. The biopolymer compositions of eluates from XAD 8/4 resins also showed no significant difference between the two methods. However, higher carbon recovery of the isolation method using SPE cartridges was found (with columns: 88.9%; with SPE: 95.9%). In addition, the proposed method using SPE cartridges packed with XAD 8/4 resins is much faster than that using general columns (with columns: 1468 min; with SPE: 485 min). The proposed isolation method is highly efficient and accurate; it is an excellent candidate method for isolating various DOMs.

Probing algogenic organic matter (AOM) by size-exclusion chromatography to predict AOM-derived disinfection by-product formation

High-performance size exclusion chromatography (HPSEC) coupled with peak-fitting technique was used to probe molecular weight (MW) properties of algogenic organic matter (AOM). The qualitative and quantitative MW information derived was used to predict AOM-derived disinfection by-product (DBP) formation. We resolved overlapping HPSEC chromatograms of all AOM samples into six major peaks with R² > 0.996. This study gave significant insight into the HPSEC profiles of AOM, in which resolved peaks A and B (biopolymers) and peak C (humic substances) showed a strong correlation with the formation of carbonaceous-DBPs (C-DBPs). This likely resulted from the abundance of aromatic structures and conjugated CC double bonds in their chemical nature. Our results also indicated the importance of algal cells, including intra-cellular and cell-bound organic matter, over extra-cellular organic matter as precursors to C-DBP formation. The application of the information extracted from HPSEC profiles associated with the fluorescent components of AOM showed great improvements in the predictability of THMs, HAAs, and C-DBPs with R² > 0.7 and p < 0.05. The outcome of this study will significantly benefit effective control of AOM-derived DBP formation by the chlorination of eutrophic waters.

Different bacterial species and their extracellular polymeric substances (EPSs) significantly affected reverse osmosis (RO) membrane fouling potentials in wastewater reclamation

Biofouling represents the "Achilles' heel" for reverse osmosis (RO) processes due to the growth of bacteria and their production of extracellular polymeric substances (EPSs). Although the microbial community structure on the RO membrane has been analysed previously, the bacterial species with a high potential of causing RO membrane fouling have not yet been identified clearly. The key components in EPSs causing RO membrane fouling have not been revealed either. In this study, seven different bacterial species were isolated from fouled RO membranes, and their EPSs were analysed in terms of the content of polysaccharides and proteins, fluorescence characteristics and molecular weight (MW) distributions. The membrane fouling potentials of these bacterial species and EPSs were evaluated based on normalized flux decline. Generally, under the same growth conditions, bacterial species with higher EPS concentrations, rather than higher cell numbers, resulted in more severe flux decline. The flux decline showed an apparent positive correlation with the EPS concentration, indicating that the concentration of EPS rather than the bacterial number mainly contributed to biofouling. Furthermore, it was found that the MW distribution was the key factor affecting the RO membrane fouling potential of EPSs from different bacterial species. With the increase in the percentage of the high-MW fraction (>10 kDa) in the EPSs from 12.6% to 74.4%, the normalized flux decline increased from 0.4 to 0.59. The components in EPSs with a MW over 10 kDa were also separated by the ultrafiltration membrane and were proven to have a higher membrane fouling potential.

Two analytical approaches quantifying the electron donating capacities of dissolved organic matter to monitor its oxidation during chlorination and ozonation

Electron-donating activated aromatic moieties, including phenols, in dissolved organic matter (DOM) partially control its reactivity with the chemical oxidants ozone and chlorine. This comparative study introduces two sensitive analytical systems to directly and selectively quantify the electron-donating capacity (EDC) of DOM, which corresponds to the number of electrons transferred from activated aromatic moieties, including phenols, to the added chemical oxidant 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonate) radical cation (i.e., ABTS^•+). The first system separates DOM by size exclusion chromatography (SEC) followed by a post-column reaction with ABTS^•+ and a spectrophotometric quantification of the reduction of ABTS^•+ by DOM. The second system employs flow-injection analysis (FIA) coupled to electrochemical detection to quantify ABTS^•+ reduction by DOM. Both systems have very low limits of quantification, allowing determination of EDC values of dilute DOM samples with <1 mg carbon per liter. When applied to ozonated and chlorinated model DOM isolates and real water samples, the two analytical systems showed that EDC values of the treated DOM decrease with increasing specific oxidant doses. The EDC decreases detected by the two systems were in overall good agreement except for one sample containing DOM with a very low EDC. The combination of EDC with UV-absorbance measurements gives further insights into the chemical reaction pathways of DOM with chemical oxidants such as ozone or chlorine. We propose the use of EDC in water treatment facilities as a readily measurable parameter to determine the content of electron-donating aromatic moieties in DOM and thereby its reactivity with added chemical oxidants.

Sorption of pharmaceuticals to soil organic matter in a constructed wetland by electrostatic interaction

There is a growing interest in the removal of pharmaceuticals from wastewater because pharmaceuticals have potential ecotoxicological effects. Among several removal mechanisms, the sorption of pharmaceuticals to sediment organic matter is an important mechanism related to the mobility of pharmaceuticals. This study investigated the sorption of pharmaceuticals to soil organic matter (SOM) by electrostatic interactions. SOM located on the surface of soil/sediment generally has a negative charge because of the functional groups present (i.e., carboxylic and phenolic groups). Thus, the electrical characteristics of SOM can induce electrical attraction with positively charged chemical compounds. In this study, SOM was extracted from soils under different aquatic plants (Acorus and Typha) in a constructed wetland in Korea. Experiments were carried out with the following three pharmaceuticals with different electrical characteristics at pH 7: atenolol (positive charge; pKa 9.5), carbamazepine (neutral; no pKa), and ibuprofen (negative charge; pKa 4.9). The SOM in the Acorus pond had a higher hydrophobicity and electrical charge density than that in the Typha pond. Regarding the sorption efficiency between SOM and charged pharmaceuticals, atenolol showed highest sorption efficiency (~60%), followed by carbamazepine (~40%) and ibuprofen (<~30%). In addition, the removal efficiency of the targeted pharmaceuticals in the constructed wetland was estimated by comparing the concentrations of the pharmaceuticals at sampling points with flowing water. The results showed that the removal efficiency of atenolol and carbamazepine was almost 50%, whereas that of ibuprofen was only ~10%. A comparison of the results of lab-scale and field experiments showed that electrostatic interaction is one of the major pharmaceutical removal mechanisms in a constructed wetland.

Advanced Oxidation Processes and Nanofiltration to Reduce the Color and Chemical Oxygen Demand of Waste Soy Sauce

Currently, the ozone (O3) oxidation efficiency in the treatment of waste soy sauce provides 34.2% color removal and a 27.4% reduction in its chemical oxygen demand (COD). To improve the O3 oxidation efficiency, hydrogen peroxide (H2O2) is used to cause a H2O2/O3 process. In H2O2/O3 process experiments, a previously optimized pH of 11 and applied O3 dose of 50 mg L−1 were used and the H2O2/O3 ratio was varied between 0.1 and 0.9 in intervals of 0.2. The results show that an H2O2/O3 ratio of 0.3 results in the highest efficiencies in terms of color removal (51.6%) and COD reduction (33.8%). Nanofiltration (NF) was used to pretreat the waste soy sauce to improve color removal and COD reduction. The results showed that NF with an NE-70 membrane results in 80.8% color removal and 79.6% COD reduction. Finally, the combination of NF and H2O2/O3 process resulted in the best treatment efficiency: 98.1% color removal and 98.2% COD reduction. Thus, NF & H2O2/O3 process can be considered as one of the best treatment methods for waste soy sauce, which requires high intrinsic color removal and COD reduction efficiencies.

Low risk posed by engineered and incidental nanoparticles in drinking water

Natural nanoparticles (NNPs) in rivers, lakes, oceans and ground water predate humans, but engineered nanoparticles (ENPs) are emerging as potential pollutants due to increasing regulatory and public perception concerns. This Review contrasts the sources, composition and potential occurrence of NNPs (for example, two-dimensional clays, multifunctional viruses and metal oxides) and ENPs in surface water, after centralized drinking water treatment, and in tap water. While analytical detection challenges exist, ENPs are currently orders of magnitude less common than NNPs in waters that flow into drinking water treatment plants. Because such plants are designed to remove small-sized NNPs, they are also very good at removing ENPs. Consequently, ENP concentrations in tap water are extremely low and pose low risk during ingestion. However, after leaving drinking water treatment plants, corrosion by-products released from distribution pipes or in-home premise plumbing can release incidental nanoparticles into tap water. The occurrence and toxicity of incidental nanoparticles, rather than ENPs, should therefore be the focus of future research.

Humic substances in Fluvisols of the Lower Vistula floodplain, North Poland

The present study describes properties of humic substances of the Fluvisols (the Lower Vistula, Poland). Fluvisols under agricultural management (arable soil and grassland) were sampled from the surface horizon 50, 200, 600, and 900 m from the Vistula River. The content of carbon in the fractions of humic acids (C_HAs), fulvic acids (C_FAs), and humins (C_HUMIN) as well as the content of dissolved organic carbon (DOC) were assayed. The organic matter of the soils that were sampled 200 m from the river demonstrated a lowest share of the humic acids (HAs) and fulvic acids (FAs). The percentage share of the hydrophilic fractions (HIL) in the HAs and, as a result the value of the HIL/ΣHOB ratio, increased with the distance from the riverbed. The HAs of the soils located further from the riverbed had a higher degree of humification compared to the HAs of the soils that were sampled 50 and 200 m away. Based on the research results, it was determined that the properties of HAs can be used to evaluate the effect of flood events, their location, and scope on the transformation of the organic matter in fluvial sediments.

Characterization of effluent organic matter from different coking wastewater treatment plants

Effluent organic matter (EfOM) in bio-treated wastewater generally has negative impacts on advanced wastewater treatment processes. Thus, a comprehensive characterization of EfOM would help determine feasibility of wastewater treatment. The aim of this work was to characterize EfOM originating from four coking wastewater treatment plants (WTPs) in China, using specific UV absorbance (SUVA), EfOM fractionation, size exclusion chromatography, and excitation-emission matrix (EEM) fluorescence spectroscopy. It was found that the predominant species in all the EfOM samples were hydrophobic compounds with high SUVA values. The molecular weight (MW) distribution of the sampled EfOM was in the range of 300-1500 Da, and stronger UV absorbance was observed in the high MW (＞ 500 Da) region. The EEM fluorescence spectra showed that aromatic compounds accounted for a large proportion of the sampled EfOM based on the fluorescence regional integration technique. The abovementioned analysis highlights the similarities in the characteristics of the EfOM originating from different coking WTPs, regardless of treatment plant design. Meanwhile, significant differences between the characteristics of the EfOM in coking wastewater and municipal wastewater were observed.

Differences in behaviour of three biopolymer constituents in coagulation with polyaluminium chloride: Implications for the optimisation of a coagulation-membrane filtration process

Coagulation is often applied as a pre-treatment for membrane processes to reduce dissolved organic matter and to prevent membrane fouling. Biopolymers (BPs) have repeatedly been reported as major organic foulants, and coagulation conditions such as pH or dose have been optimised to minimise the remaining BPs. Optimisation however remains problematic because of the complex and heterogenetic nature of BP. In this study, the behaviour of several BP fractions in a coagulation process was investigated by excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) following liquid chromatography (LC)-fractionation. Using a series of jar tests, we found that BP removal depends on the type of source water, reflecting differences in charge neutralisation conditions in three samples of natural water despite nearly identical processes for removing humic substances. This result demonstrates the complexity of optimisation for BP coagulation. Fractionation of EEM-PARAFAC to BP by LC showed that at least three organic component groups (C1, C2 and C3) constitute BP. C1 is tryptophan-like organic matter that is often found in wastewater effluent, C2 is tyrosine-like organic matter that has a phenolic chemical structure, and C3 is a humic-like substance. C1 was removed thoroughly at acidic pH but not at neutral pH, while the removal of C2 was inefficient even with a significant change in pH or dose, indicating similar difficulties in a coagulation process. The difference in components C1 and C2 may partly explain the difference in efficiencies of removal of BP in water from different sources. Our investigation suggests that the optimisation or selection of appropriate pre-treatment processes for membrane systems should be substantially based on the composition of BPs (e.g., C1 and C2 components).

Impact of the Interaction between Aquatic Humic Substances and Algal Organic Matter on the Fouling of a Ceramic Microfiltration Membrane

The influence of the interaction between aquatic humic substances and the algal organic matter (AOM) derived from Microcystis aeruginosa on the fouling of a ceramic microfiltration (MF) membrane was studied. AOM alone resulted in a significantly greater flux decline compared with Suwannee River humic acid (HA), and fulvic acid (FA). The mixture of AOM with HA and FA exhibited a similar flux pattern as the AOM alone in the single-cycle filtration tests, indicating the flux decline may be predominantly controlled by the AOM in the early filtration cycles. The mixtures resulted in a marked increase in irreversible fouling resistance compared with all individual feed solutions. An increase in zeta potential was observed for the mixtures (becoming more negatively charged), which was in accordance with the increased reversible fouling resistance resulting from enhanced electrostatic repulsion between the organic compounds and the negatively-charged ceramic membrane. Dynamic light scattering (DLS) and size exclusion chromatography analyses showed an apparent increase in molecular size for the AOM-humics mixtures, and some UV-absorbing molecules in the humics appeared to participate in the formation of larger aggregates with the AOM, which led to greater extent of pore plugging and hence resulted in higher irreversible fouling resistance.

High Pressure Size Exclusion Chromatography (HPSEC) Determination of Dissolved Organic Matter Molecular Weight Revisited: Accounting for Changes in Stationary Phases, Analytical Standards, and Isolation Methods

We reassessed the molecular weight of dissolved organic matter (DOM) determined by high pressure size exclusion chromatography (HPSEC) using measurements made with different columns and various generations of polystyrenesulfonate (PSS) molecular weight standards. Molecular weight measurements made with a newer generation HPSEC column and PSS standards from more recent lots are roughly 200 to 400 Da lower than initial measurements made in the early 1990s. These updated numbers match DOM molecular weights measured by colligative methods and fall within a range of values calculated from hydroxyl radical kinetics. These changes suggest improved accuracy of HPSEC molecular weight measurements that we attribute to improved accuracy of PSS standards and changes in the column packing. We also isolated DOM from wetlands in the Prairie Pothole Region (PPR) using XAD-8, a cation exchange resin, and PPL, a styrene-divinylbenzene media, and observed little difference in molecular weight and specific UV absorbance at 280 nm (SUVA₂₈₀) between the two solid phase extraction resins, suggesting they capture similar DOM moieties. PPR DOM also showed lower SUVA₂₈₀ at similar weights compared to DOM isolates from a global range of environments, which we attribute to oxidized sulfur in PPR DOM that would increase molecular weight without affecting SUVA₂₈₀.

Nanofiltration and Tight Ultrafiltration Membranes for Natural Organic Matter Removal-Contribution of Fouling and Concentration Polarization to Filtration Resistance

Nanofiltration (NF) and tight ultrafiltration (tight UF) membranes are a viable treatment option for high quality drinking water production from sources with high concentrations of contaminants. To date, there is limited knowledge regarding the contribution of concentration polarization (CP) and fouling to the increase in resistance during filtration of natural organic matter (NOM) with NF and tight UF. Filtration tests were conducted with NF and tight UF membranes with molecular weight cut offs (MWCOs) of 300, 2000 and 8000 Da, and model raw waters containing different constituents of NOM. When filtering model raw waters containing high concentrations of polysaccharides (i.e., higher molecular weight NOM), the increase in resistance was dominated by fouling. When filtering model raw waters containing humic substances (i.e., lower molecular weight NOM), the increase in filtration resistance was dominated by CP. The results indicate that low MWCO membranes are better suited for NOM removal, because most of the NOM in surface waters consist mainly of humic substances, which were only effectively rejected by the lower MWCO membranes. However, when humic substances are effectively rejected, CP can become extensive, leading to a significant increase in filtration resistance by the formation of a cake/gel layer at the membrane surface. For this reason, cross-flow operation, which reduces CP, is recommended.

Ferrous iron/peroxymonosulfate oxidation as a pretreatment for ceramic ultrafiltration membrane: Control of natural organic matter fouling and degradation of atrazine

Ferrous iron/peroxymonosulfate (Fe(II)/PMS) oxidation was employed as a pretreatment method for ultrafiltration process to control membrane fouling caused by natural organic matter, including humic acid (HA), sodium alginate (SA), bovine serum albumin (BSA), and their mixture (HA-SA-BSA). To evaluate the mechanism of fouling mitigation, the effects of Fe(II)/PMS pretreatment on the characteristics of feed water were examined. The degradation of atrazine (ATZ) was also investigated and the species of generated radicals were preliminarily determined. Under the test exposure (15 and 50 μM), Fe(II)/PMS pretreatment effectively mitigated membrane fouling caused by HA, SA and HA-SA-BSA mixture, and the performance improved with the increase of Fe(II) or PMS dose; whereas aggravated BSA fouling at lower doses and fouling alleviation was observed only at a higher dose (50/50 μΜ). The fouling mitigation was mainly attributed to the effective reduction of organic loadings by coagulation with in-situ formed Fe(III). Its performance was comparable or even slightly higher than single coagulation with Fe(III), most likely due to the oxidation by Fe(II)/PMS process. Fe(II)/PMS oxidation showed better performance in reducing DOC and UV₂₅₄, fluorescence intensities of fluorescent components and UV-absorbing compounds than single coagulation. In addition, Fe(II)/PMS pretreatment was efficient in ATZ degradation due to the generation of sulfate and hydroxyl radicals, whereas coagulation was ineffective to remove it.

Prediction of the adsorption capacities for four typical organic pollutants on activated carbons in natural waters

A new model is developed to predict the competitive adsorption isotherms of atrazine, methyl tertiary butyl ether (MTBE), 2-methylisoborneol (2-MIB) and 2,4,6-trichlorophenol onto activated carbons (ACs) in natural water. Based on the Polanyi-Dubinin (PD) equation, with the limiting pore volume of adsorbent estimated from the pore size distribution data, and the Ideal adsorbed solution theory - equivalent background compound (IAST-EBC) model approximation, the model takes into account both the properties of ACs and the impact of natural organic matters in water. Only one set of isotherm in deionized water and one set in natural water are needed to obtain the parameters for the prediction of adsorption isotherms onto different ACs in natural water. The model was employed for the predictions of adsorption capacities for atrazine, MTBE, 2-MIB and 2,4,6-trichlorophenol onto 14 ACs in 22 synthetic and natural waters reported in 9 references, with errors between 14.9% and 44.5% SDEV only. The results suggest that in the proposed PD-IAST-EBC approach, prediction of adsorption capacity for organic compounds onto different ACs in the same natural water is feasible, if the ACs are thermally activated with known pore size information. The model may provide a simple approach for the prediction of adsorption of organic compounds in natural water, and thus greatly reduces the effort required for water utilities when change of AC is needed.

Characterizing Ohio River NOM Variability and Reconstituted-Lyophilized NOM as a Source Surrogate

Natural organic matter (NOM) was collected, concentrated, and lyophilized on a monthly basis for 15 months to create a temporal NOM library and assess seasonal variability of untreated Ohio River water. Using fluorescence spectroscopy with parallel factor analysis, similar spectral components for both the ultrafiltered source water (UF1X) and reconstituted lyophilized NOM were observed in a two-component model throughout the study, with overall average emission and excitation wavelengths of 418 nm and 270 nm, respectively, for component 1 and 482 nm and 370 nm, respectively, for component 2. Fluorescence spectroscopy, high-pressure liquid chromatography-size exclusion chromatography, and elemental analysis indicated that the NOM was humic-like during the study with only small seasonal changes. Data from these analyses also demonstrated similarity between results for UF1X, reverse osmosis-concentrated NOM, and reconstituted- lyophilized NOM, validating the use of the reconstituted- lyophilized NOM as a surrogate for its source.

Fractionation and size-distribution of metal and metalloid contaminants in a polluted groundwater rich in dissolved organic matter

We investigated the concentration levels, fractionation and molecular weight distribution (MWD) of dissolved organic matter (DOM) and metals (V, Cr, Co, Ni, Cu, Zn, As, Cd, Sn, Ba, Hg and Pb) in a polluted groundwater from an industrial area in Northern Sweden. DOM was mainly recovered in the hydrophobic acidic and hydrophobic neutral sub-fractions (45 and 35%, respectively) while most metals were found in the acidic sub-fractions (46-93%) except for V, Fe and As, which were predominant in the basic sub-fractions (74-93%) and Cd in the neutral ones (50%). DOM exhibited a broad MWD in groundwaters, usually from 5 to 200kDa and was dominated by high molecular weight hydrophobic acids, low molecular weight hydrophilic acids and hydrophilic neutral compounds. Most of the studied metals (Fe, Cr, Co, Sn, Ba, Hg) were associated with the high molecular weight DOM fraction (ca. 40-100kDa). Cu, Pb, Zn, Cd and Ni interacted with a broad range of DOM size fractions but were still most abundant in the high molecular weight fraction. Few metal/metalloids (As, V and Cr in some cases) presented a very weak affinity for DOM and presumably existed predominantly as "free" inorganic ions in solution.

Identifying the major fluorescent components responsible for ultrafiltration membrane fouling in different water sources

Three-dimensional fluorescence excitation-emission matrix (EEM) coupled with parallel factor analysis (PARAFAC) was performed for a total of 18 water samples taken from three water sources (two lakes and one wastewater treatment plant (WWTP) secondary effluent), with the purpose of identifying the major ultrafiltration (UF) membrane foulants in different water sources. Three fluorescent components (C1, C2 and C3) were identified, which represented terrestrially derived humic-like substances (C1), microbially derived humic-like substances (C2), and protein-like substances (C3). The correlations between the different fluorescent components and UF membrane fouling were analyzed. It was shown that for the WWTP secondary effluent, all three components (C1, C2 and C3) made a considerable contribution to the irreversible and total fouling of the UF membrane. However, for the two lakes, only the C3 exhibited a strong correlation with membrane fouling, indicating that the protein-like substances were the major membrane foulants in the lake waters. Significant attachment of C1, C2 and C3 to the UF membrane was also confirmed by mass balance analyses for the WWTP secondary effluent; while the attachment of C1 and C2 was shown to be negligible for the two lakes. The results may provide basic formation for developing suitable fouling control strategies for sustainable UF processes.

Simple, quantitative method for low molecular weight dissolved organic matter extracted from natural waters based upon high performance counter-current chromatography

A simple, high-performance counter-current chromatography method with sequential UV absorbance (254 nm) and evaporative light scattering detection (ELSD) was developed for the quantification of pre-extracted low molecular weight dissolved organic matter (DOM) extracted from natural waters. The method requires solid-phase extraction (SPE) extraction of only small volumes of water samples, here using poly(styrenedivinylbenzene)-based extraction cartridges (Varian PPL). The extracted and concentrated DOM was quantified using reversed-phase high-performance counter-current chromatography (HPCCC), with a water/methanol (5:5) mobile phase and hexane/ethyl acetate (3:7) stationary phase. The critical chromatographic parameters were optimised, applying a revolution speed of 1900 rpm and a flow-rate of 1 mL min(-1). Under these conditions, 50 μL of extracted DOM solution could be injected and quantified using calibration against a reference natural dissolved material (Suwannee River), based upon UV absorbance at 254 nm and ELSD detection. Both detection methods provided excellent linearity (R(2) > 0.995) for DOM across the concentration ranges of interest, with limits of detection of 4 μg ml(-1) and 7 μg ml(-1) for ELSD and UV absorbance, respectively. The method was validated for peak area precision (<5%), and accuracy and recovery based upon spiking seawater samples prior to extraction, together with DOM solutions post-extraction (>95% recovery). The developed method was applied to the determination of the concentration of DOM in seawater, based upon initial sample volumes as small as 20 mL.

Tracking the monthly changes of dissolved organic matter composition in a newly constructed reservoir and its tributaries during the initial impounding period

Understanding the roles of inland reservoirs becomes increasingly important with respect to global carbon cycling as well as water resource management due to the unprecedented demand for construction in recent decades. In this study, the dissolved organic matter (DOM) quantity and quality in a newly constructed dam reservoir and its tributaries were monitored monthly during the initial impounding period (July to November 2014) using a size exclusion chromatography (SEC) with online organic carbon detector (OCD). The highest values were observed in the month of August with the highest precipitation for the bulk dissolved organic carbon (DOC), specific UV absorbance (SUVA), and most of the assigned size fractions (except for biopolymers) in the tributaries, indicating that allochthonous sources of DOM were dominant in the feeding stream waters of the reservoir. The bulk DOC and high molecular weight humic substance fraction (∼1 kDa) were generally co-varied with the monthly precipitation in the tributaries, while building blocks (350-500 Da), and low molecular weight (LMW) acids and neutrals showed different trends. In a dam site, the smaller molecular fractions became more abundant during the dry season (September to November), presumably due to the in-reservoir processes such as photo- and bio-degradation. Our results also revealed that storms mobilized a large amount of highly aromatic soil-derived DOM to the reservoir. A depth profile at the dam site showed the water is well mixed up to a depth of ∼20 m. The SEC-OCD data coupled with non-metric multidimensional scaling provided a clear visualization of the spatiotemporal variations in DOM composition, which shed new light on the DOM composition formed in a newly constructed dam reservoir and also on the strategies for future water treatment options.

The effect of vegetation and soil texture on the nature of organics in runoff from a catchment supplying water for domestic consumption

The influence of vegetation and soil texture on the concentration and character of dissolved organic matter (DOM) present in runoff from the surface and sub-surface of zero order catchments of the Myponga Reservoir-catchment (South Australia) was investigated to determine the impacts of catchment characteristics and land management practices on the quality of waters used for domestic supply. Catchments selected have distinct vegetative cover (grass, native vegetation or pine) and contrasting texture of the surface soil horizon (sand or clay loam/clay). Water samples were collected from three slope positions (upper, middle, and lower) at soil depths of ~30 cm and ~60 cm in addition to overland flows. Filtered (0.45 μm) water samples were analyzed for dissolved organic carbon (DOC) and UV-visible absorbance and by F-EEM and HPSEC with UV and fluorescence detection to characterize the DOM. Surface and sub-surface runoff from catchments with clay soils and native vegetation or grass had lower DOC concentrations and lower relative abundances of aromatic, humic-like and high molecular weight organics than runoff from sandy soils with these vegetative types. Sub-surface flows from two catchments with Pinus radiata had similar DOC concentrations and DOM character, regardless of marked variation in surface soil texture. Runoff from catchments under native vegetation and grass on clay soils resulted in lower DOC concentrations and hence would be expected to have lower coagulant demand in conventional treatment for potable water supply than runoff from corresponding sandy soil catchments. However, organics in runoff from clay catchments would be more difficult to remove by coagulation. Surface waters from the native vegetation and grass catchments were generally found to have higher relative abundance of organic compounds amenable to removal by coagulation compared with sub-surface waters. Biophysical and land management practices combine to have a marked influence on the quality of source water used for domestic supply.

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.