Natural Organic Matter Compounds Research Articles

Application of Fenton's Reaction for Removal of Organic Matter from Groundwater.

In this study, the effectiveness of the Fenton process in removing natural organic matter (NOM) from groundwater was investigated. The subject of this study is groundwater characterised by increased content of NOM and iron (II) compounds. In laboratory-scale studies, the influence of the ratio of concentrations of Fe(II) ions, which are naturally occurring in groundwater, to hydrogen peroxide (H2O2) as well as oxidation time and pH on the removal efficiency of organic matter was determined. Indicators such as total organic carbon (TOC), dissolved organic carbon (DOC), UV absorbance at 254 nm (UV254), UV absorbance at 272 nm (UV272), and specific UV absorbance (SUVA254) were used to quantitatively and qualitatively assess the organic substances present in the raw water and after oxidation with Fenton's reagent. Analysis of the results obtained showed that the highest removal efficiency of organic substances in the deep oxidation process using the Fenton reaction was obtained for a concentration ratio of Fe(II) to H2O2 = 1:5. Acidification of the water samples to a pH of about 4 and extending the oxidation time to 30 min significantly increased the removal efficiency of organic substances including mainly dissolved organic substances containing aromatic rings. The organic substances containing aromatic rings, determined at a wavelength of 254 nm, were degraded to other organic intermediates.

High throughput identification of carbonyl compounds in natural organic matter by directional derivatization combined with ultra-high resolution mass spectrometry

Carbonyl compounds are important components of natural organic matter (NOM) with high reactivity, so that play a pivotal role in the dynamic transformation of NOM. However, due to the lack of effective analytical methods, our understanding on the molecular composition of these carbonyl compounds is still limited. Here, we developed a high-throughput screening method to detect carbonyl molecules in complex NOM samples by combining chemical derivatization with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). In six different types of dissolved organic matter (DOM) samples tested in this study, 20–30 % of detected molecules contained at least one carbonyl group, with relative abundance accounted for 45–70 %. These carbonyl molecules displayed lower unsaturation level, lower molecular weight, and higher oxidation degree compared to non-carbonyl molecules. More importantly, the measured abundances of carbonyl molecules were consistent with the results of 13C nuclear magnetic resonance (NMR) analysis. Based on this method, we found that carbonyl molecules can be produced at DOM-ferrihydrite interface, thus playing a role in shaping the molecular diversity of DOM. This method has broad application prospects in screening carbonyl compounds from complex mixtures, and the same strategy can be used to directional identification of molecules with other functional groups as well.

Efficient PFAS prioritization in non-target HRMS data: systematic evaluation of the novel MD/C-m/C approach

Non-target screening (NTS) based on high-resolution mass spectrometry (HRMS) is necessary to comprehensively characterize per- and polyfluoroalkyl substances (PFAS) in environmental, biological, and technical samples due to the very limited availability of authentic PFAS reference standards. Since in trace analysis, MS/MS information is not always achievable and only selected PFAS are present in homologous series, further techniques to prioritize measured HRMS data (features) according to their likelihood of being PFAS are highly desired due to the importance of efficient data reduction during NTS. Kaufmann et al. (J AOAC Int, 2022) presented a very promising approach to separate selected PFAS from sample matrix features by plotting the mass defect (MD) normalized to the number of carbons (MD/C) vs. mass normalized to the number of C (m/C). We systematically evaluated the advantages and limitations of this approach by using ~ 490,000 chemical formulas of organic chemicals (~ 210,000 PFAS, ~ 160,000 organic contaminants, and 125,000 natural organic matter compounds) and calculating how efficiently, and especially which, PFAS can be prioritized. While PFAS with high fluorine content (approximately: F/C > 0.8, H/F < 0.8, mass percent of fluorine > 55%) can be separated well, partially fluorinated PFAS with a high hydrogen content are more difficult to prioritize, which we discuss for selected PFAS. In the MD/C-m/C approach, even compounds with highly positive MDs above 0.5 Da and hence incorrectly assigned to negative MDs can still be separated from true negative mass defect features by the normalized mass (m/C). Furthermore, based on the position in the MD/C-m/C plot, we propose the estimation of the fluorine fraction in molecules for selected PFAS classes. The promising MD/C-m/C approach can be widely used in PFAS research and routine analysis. The concept is also applicable to other compound classes like iodinated compounds.Graphical

Assessment of heat and radiation impacts on natural organic matter composition in bentonite for used nuclear fuel disposal

Bentonite clay (Wyoming, USA) is proposed as a buffer layer for the engineered barrier system for the deep geologic repository to store Canada's used nuclear fuels in the long-term. The presence of natural organic matter (NOM) in the mined bentonite may support microbial activity which may promote the corrosion of used fuel containers. The NOM found in Wyoming-type bentonite is diagenetically altered, however, there is limited knowledge about how NOM chemistry may change with heat and radiation when exposed to the proposed deep geologic repository conditions. To investigate this further, molecular-level techniques were used to analyze NOM compositional differences in bentonite with different heat (30–105 °C for 3 days, and 90 °C for 14, 28 and 42 days) and gamma-radiation exposure (100 kGy for 3 days). Elemental analysis results indicated that all bentonite samples exhibited low total organic carbon concentrations (0.15–0.27%) and 1.6–3.3% of these were in the form of extractable dissolved organic carbon. Solution-state 1H nuclear magnetic resonance (NMR) and solid-state 13C NMR analyses revealed that chemical signatures of dissolved organic matter and overall NOM composition did not vary between samples. Slightly increased concentrations of short-chain (C9-C19) n-alkanoic acids were observed with heat (14, 28 and 42 days at 90 °C), which is likely due to the oxidation of long-chain (≥C20) n-alkanes or n-alkanols. However, the broader assessment of NOM composition via principal component analysis of forty-four targeted NOM compounds indicated no significant differences after heat or radiation exposure. Collectively, the molecular-level analyses indicate that heat and radiation only imparted nanogram-level differences in some targeted compound concentrations, but the overall NOM chemistry was not altered. These results expand the understanding of NOM chemistry in bentonite clay and suggest that under the conditions tested, NOM composition in bentonite was largely insensitive to heat and radiation exposure. Further work is warranted to investigate longer exposure durations and the overall stability of NOM in a deep geologic repository setting.

Mitigation of ultrafiltration membrane fouling by a simulated sunlight-peroxymonosulfate system with the assistance of irradiated NOM

Oxidation pretreatments prior to ultrafiltration are hindered by the need for energy input and sludge disposal. Herein, a simulated sunlight-induced natural organic matter (NOM) for peroxymonosulfate (PMS) activation was used as pretreatment to alleviate ultrafiltration membrane fouling caused by NOM itself in the Songhua River water. When light intensity was over 100 mW/cm2, the pretreatment removed NOM effectively, characterized with UV254, dissolved organic carbon (DOC) and maximum fluorescent intensity (Fmax), and improved filtration flux. At 200 mW/cm2 light intensity and 0.5 mM PMS, 57.5% of UV254 and 18.5% of DOC were removed, and humic-like fluorescent component was degraded by 84%-94% while ∼60% for protein-like substance. Membrane flux was increased by 94%, and reversible and irreversible fouling resistances were reduced by 62.4% and 51.9%, respectively. Both total fouling index (TFI) and hydraulic irreversible fouling index (HIFI) were moderately correlated with the DOC, whereas they prominently correlated with the UV254 and the Fmaxs of all fluorescence components, which could be served as key indicators to predict and control membrane fouling. Mathematical modeling showed that the pretreatment alleviated the fouling in the membrane pores and cake layer. The simulated sunlight-induced NOM (3NOM* and eaq¯) could activate PMS to form active species, which enabled to oxidize high molecular weight (MW) substances and mineralize low MW compounds in NOM as well as hinder their linking with inorganic cations, thereby reducing organic and inorganic membrane fouling simultaneously. This study may provide a new strategy for decentralized potable water treatment, especially in a single household or community.

Impact of the modernized technology on the quality of water supplied to the extended distribution system of the city of Pozna\u0144

The paper presents the results of a long-term study covering the development, implementation and operation of the second stage of water treatment (i.e. ozonation and subsequent granular active carbon (GAC) filtration) in the “Mosina” water treatment station supplying drinking water to the city of Poznań. The basis for the modernisation of the system was the high reactivity of the natural organic matter (NOM) present in the treated water with the disinfectant (in this case chlorine dioxide) resulting in an increased demand for ClO2 and reduced microbiological stability of the water. During the study it was shown that simple carboxylic acids are generated during ozonation and their presence can be an indicator of the microbiological stability of the treated water. However, these compounds are effectively removed from water during filtration through biologically active GAC filters. It was also shown that the best and cheapest parameter allowing to control water quality at individual stages of its treatment is UV absorbance, which shows reactive components of NOM removal efficiency in the technological sequence. The effectiveness of the modernisation of the technological system was evaluated on the basis of the disinfectant demand as well as on the basis of selected carboxylic acids concentration in the intake points on the water supply network fed with water from the WTS “Mosina”. At the last stage of the study, it was observed that the concentration of carboxylic acids in the distribution network was significantly reduced and stabilised, and a low dose of chlorine dioxide did not cause their re-formation. As a result of the modernisation, a new balance was achieved between the disinfectants used and the NOM compounds present in the treated water. Thus, the results confirmed that properly conducted pilot studies are a required element in planning of modernisation changes for water supply facilities.

Role of NOM in the Photolysis of Chlorine and the Formation of Reactive Species in the Solar/Chlorine System.

The solar/chlorine system has been proposed as a novel advanced oxidation process (AOP) for efficient pollutant degradation and water disinfection by producing a series of reactive species including hydroxyl radicals (HO•), chlorine radicals (Cl•), and so forth. In this study, the role of natural organic matter (NOM) in the photolysis of free available chlorine (FAC) and the formation of HO• and Cl• in the solar/chlorine system was investigated employing nitrobenzene and benzoic acid as selective chemical probes. The decay rate of FAC was significantly accelerated in the presence of NOM at pH 5.5 under simulated solar irradiation, likely due to the photoreaction between FAC and the photoexcited NOM. The decay rate of FAC increased upon increasing the electron-donating capacity of NOM, which indicated that phenolic components play a significant role in the photodegradation of FAC. This acceleration mechanism was further verified using 4-nitrophenol as a model phenolic compound. NOM promoted Cl• formation and quenched HO• in the solar/chlorine system. The proposed reaction mechanism included the reaction of excited singlet phenolic compounds in NOM with FAC, which yielded Cl•. This study provides a useful insight into future applications for using the solar/chlorine system as a novel AOP for wastewater treatment or disinfection.

Aromaticity Index with Improved Estimation of Carboxyl Group Contribution for Biogeochemical Studies.

Natural organic matter (NOM) components measured with ultrahigh-resolution mass spectrometry (UHRMS) are often assessed by molecular formula-based indices, particularly related to their aromaticity, which are further used as proxies to explain biogeochemical reactivity. An aromaticity index (AI) is calculated mostly with respect to carboxylic groups abundant in NOM. Here, we propose a new constrained AIcon based on the measured distribution of carboxylic groups among individual NOM components obtained by deuteromethylation and UHRMS. Applied to samples from diverse sources (coal, marine, peat, permafrost, blackwater river, and soil), the method revealed that the most probable number of carboxylic groups was two, which enabled to set a reference point n = 2 for carboxyl-accounted AIcon calculation. The examination of the proposed AIcon showed the smallest deviation to the experimentally determined index for all NOM samples under study as well as for individual natural compounds obtained from the Coconut database. In particular, AIcon performed better than AImod for all compound classes in which aromatic moieties are expected: aromatics, condensed aromatics, and unsaturated compounds. Therefore, AIcon referenced with two carboxyl groups is preferred over conventional AI and AImod for biogeochemical studies where the aromaticity of compounds is important to understand the transformations and fate of NOM compounds.

Molecular composition of halobenzoquinone precursors in natural organic matter in source water

Halobenzoquinones (HBQs) are emerging disinfection byproducts generated during the reaction of chlorine disinfectant with natural organic matter (NOM) in source water. In this study, the correlations between molecular weight and HBQs generation of river NOM was evaluated. The compositional and functional characteristics of primary HBQs precursors were revealed by using Orbitrap mass spectrometry combined with molecular tagging. The NOM fraction larger than 50 kDa resulted in approximately 9 times more HBQs (50.9 ± 2.7 ng/mgC) than low molecular weight fractions. Significant correlations were found between the yields of HBQs and lignin-like and highly oxygen compounds in NOM, suggesting their critical roles in HBQs formation. Derivatizating the aldehydes, ketones, hydroxyl and carboxyl groups in NOM could reduce HBQs yields by 90.7%–100%. Unraveling the molecular characteristics of HBQs precursors in NOM would greatly benefit the prediction of HBQs yields of different source water, and develop more efficient disinfection byproduct control strategies.

Photocatalytic Bactericidal Performance of LaFeO3 under Solar Light in the Presence of Natural Organic Matter: Spectroscopic and Mechanistic Evaluation

Solar photocatalytic inactivation (SPCI) of E. coli as the indicator microorganism using LaFeO3 (LF) has already been investigated under various experimental conditions, excluding any role of natural organic matter (NOM). However, comprehensive information about the behavior of E. coli and its inactivation mechanism in the presence of NOM, as well as the behavior of NOM components via solar photocatalysis using LF as a photocatalyst, has prime importance in understanding real natural water environments. Therefore, in this study, further assessment was devoted to explore the influence of various NOM representatives on the SPCI of E. coli by using LF as a novel non-TiO2 photocatalyst. The influence of NOM as well as its sub-components, such as humic acids (HA) and fulvic acids (FA), was also investigated to understand different NOM-related constituents of real natural water conditions. In addition to spectroscopic and mechanistic investigations of cell-derived organics, excitation emission matrix (EEM) fluorescence spectra with parallel factor multiway analysis (PARAFAC) modeling revealed further information about the occurrence and/or disappearance of NOM-related and bacteria-related fluorophores upon LF SPCI. Both the kinetics as well as the mechanism of the LF SPCI of E. coli in the presence of NOM compounds displayed substrate-specific variations under all conditions.

Online Counter Gradient LC-FT-ICR-MS Enables Detection of Highly Polar Natural Organic Matter Fractions.

Natural organic matter (NOM) is a highly complex mixture of natural organic molecules. The recent developments in NOM molecular characterization methods have shown that ESI-FT-ICR hyphenated with liquid chromatography (LC) is a promising approach to also obtain chemical information (such as polarity and molecular size) about NOM molecules. However, due to changing solvent composition during gradient elution in LC-FT-ICR-MS, ionization conditions also change throughout the chromatographic separation process. In this study, we applied a post-LC column counter gradient (CG) to ensure stable solvent conditions for transient ESI-MS signals. Suwanee River Fulvic Acid (SRFA) standard and a peat pore water were used as representative dissolved NOM samples for method development and validation. Our results show that in polar NOM fractions (which elute with <50% methanol) the TIC intensity and number of assigned molecular formulas were increased by 48% and 20%, as compared to the standard gradient (SG) method. Further application of a Q-isolation and selective ion accumulation for low abundance fractions revealed over 3 times more molecular formulas (especially for CHNO, CHOS, CHNOS formula classes) than in full scan mode. The number of detected highly polar NOM compounds (with elemental ratios H/C < 1, O/C > 0.6) were more than 20 times larger for CG-LC mode as compared to direct infusion (DI) (5715 vs 266 MF). We conclude that the application of a postcolumn counter gradient in LC-FT-ICR-MS analyses of NOM offers novel insight into the most polar fractions of NOM which are inaccessible in conventional DI measurements.

Tailored mesoporous biochar sorbents from pinecone biomass for the adsorption of natural organic matter from lake water

Natural organic matter (NOM) raises major issues for drinking water treatment including undesirable taste and color, formation of carcinogenic disinfection by-products, and promotion of microbial regrowth in the water distribution system. As such, mesoporous biochars have been tailored from pine-forestry by-products for treating NOM and color causing compounds from drinking water sources, such as lakes. Herein, several tailored biochars are fabricated via two procedures: pre-pyrolysis/activation/post-pyrolysis and activation/post-pyrolysis processes, using NaOH and ZnCl2 activators to improve the surface chemistry and porous structure for higher NOM adsorption. The mesoporous biochars, pristine biochars, and pinecone biomass are characterized via several analysis methods including Brunauer, Emmett and Teller surface area measurement (BET), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Batch experiments are conducted to study the adsorption isotherm, kinetics and mechanism along with desorption. Characterization revealed effective characteristics of tailored biochars for NOM adsorption including mesoporous structure, remarkable surface area (up to 1470 m2/g), high thermal stability, and elevated carbon content. All the tailored biochars showed improved removal capacities for NOM and color compounds from real lake water samples compared with those of the pinecone biomass and pristine biochars. The most promising tailored biochar (herein named as TB-N-I) was developed by NaOH modification via pre- and post-pyrolysis processes. With the lowest optimized dosage (0.25 g/L), TB-N-I removed >80% of both NOM and color from the lake water (chemical oxygen demand (COD): 13.4 and color: 53.65 mg/L), superior to the removal capacity of commercial powdered activated carbon (PAC). Acidic conditions significantly favored the adsorption, e.g. NOM removal by TB-N-I from the lake water reached 97% at pH 2. Nonlinear regression provided a good fit for Freundlich and Sips (r2 = 0.988 and Δq = 0.08) isotherms as well as pseudo-second-order kinetic models. This suggests the heterogeneous distribution of the adsorptive sites at the biochar surface and the multilayer nature of NOM adsorption. Our desorption study revealed that more alkaline solutions resulted in higher NOM desorption (30 mM NaOH > 3 mM NaOH > distilled water), yielding regenerated adsorbents with high re-adsorption capacity. Liquid chromatograph–organic carbon detection (LC-OCD) was used to study the removal of different size fractions of NOM, e.g. complex humic substances and low molar mass acids. Of significant interest, low molar mass (LMM) fraction, which are more hydrophilic and resistant to conventional treatments, were effectively removed. LC-OCD indicated that TB-N-I removed 20% more of the problematic LMM compared with that of PAC. Effective pore size distribution of tailored biochar (TB-N-I) was indicated by BET analysis and was confirmed by LC-OCD results for the adsorption of NOM fractions.

Insights into aqueous reduction of Cr(VI) by Fe3O4@NOM MNPs under irradiation: The role of carbonyl structures

This study investigates the active sites in natural organic matter (NOM) that are important for the removal of Cr(VI), by using Fe3O4 magnetic nanoparticles (MNPs) modified by NOM (Fe3O4@NOM). NaBH4 is used to selectively reduce carbonyl groups in Fe3O4@NOM MNPs to demonstrate the role of carbonyl structures in the reduction of Cr(VI), especially under irradiation. Results observed using NOM and low molecular weight compounds further demonstrated that carbonyl structures in Fe3O4@NOM MNPs, especially aromatic ketones, can strongly promote Cr(VI) reduction. This phenomenon corresponds well to a model in which charge transfer interactions occur between donors and acceptors in NOM.

Differential absorbance study of interactions between europium, soil and aquatic NOM and model compounds

This study compared the binding of europium by soil and aquatic natural organic matter (NOM) exemplified by Pahokee Peat humic acid (PPHA) and Northern Reservoir NOM, respectively. NOM/Eu3+ interactions were measured based on the differential absorbance approach. The experimental results show that the binding of Eu3+ by humic acid isolated from agricultural soil results in several features of the differential spectra that are distinct from those observed for aquatic NOM. These features may be associated with the presence in soil NOM of functional groups similar to gallic acid. The binding of Eu3+ by NOM was modeled using a phenomenological approach that accounted for the involvement of dissimilar metal-binding functionalities. This study also introduced the concept of integrated differential absorbance; the use of that parameter allowed achieving a close fit between the experimental and model data. This study presents an alternative approach to ascertain mechanisms of, and differences in the interactions of europium with model compounds and natural organic matter with the provenance from soil and surface water.

DBP alteration from NOM and model compounds after UV/persulfate treatment with post chlorination

The UV/persulfate process is an effective advanced oxidation process (AOP) for the abatement of a variety of micropollutants via producing sulfate radicals (SO4•-). However, when this technology is used to reduce target pollutants, the precursors of disinfection byproducts (DBPs), such as natural organic matter (NOM) and organic nitrogen compounds, can be altered. This study systematically investigated the DBP formation from NOM and five model compounds after UV/H2O2 and UV/persulfate treatments followed with 24 h chlorination. Compared to chlorination alone, the yields of trichloromethane (TCM) and dichloroacetonitrile (DCAN) from NOM decreased by 50% and 54%, respectively, after UV/persulfate treatment followed with chlorination, whereas those of chloral hydrate (CH), 1,1,1-trichloropropanone (1,1,1-TCP) and trichloronitromethane (TCNM) increased by 217%, 136%, and 153%, respectively. The effect of UV/H2O2 treatment on DBP formation shared a similar trend to that of UV/persulfate treatment, but the DBP formation was higher from the former. As the UV/persulfate treatment time prolonged or the persulfate dosage increased, the formation of TCM and DCAN continuously decreased, while that of CH, 1,1,1-TCP and TCNM presented an increasing and then decreasing pattern. SO4•- activated benzoic acid (BA) to form phenolic compounds that enhanced the formation of TCM and CH, while it deactivated resorcinol to decrease the formation of TCM. SO4•- reacted with aliphatic amines such as methylamine (MA) and dimethylamine (DMA) to form nitro groups, which significantly increased the formation of TCNM in post chlorination, and the rate was determined to be higher than that of HO•. This study illuminated the diverse impacts of the structures of the precursors on DBP formation after UV/persulfate treatment, and DBP alteration depended on the reactivity between SO4•- and specific precursor.

Use of carbon isotopic ratios in nontargeted analysis to screen for anthropogenic compounds in complex environmental matrices

Analytical data for ultra-high-performance liquid chromatography (UHPLC), nontargeted, high-resolution, mass-spectrometry (HR/MS) molecular features from a wide array of samples are used to calculate 13C112C(n-1)/12Cn isotopologue ratios. These ratios increase with molecular carbon number roughly following a trend defined by atmospheric carbon. When the effective source reservoir 13C/12C ratio is calculated from the isotopologue ratio (assuming a fractionation factor of unity), features in biotic samples uniformly are tightly grouped, proximate to atmospheric 13C/12C ratio. In contrast, features in soil natural organic matter (NOM), dust NOM and anthropogenic compounds range from proximate to relatively divergent from atmospheric 13C/12C. For the NOM, 13C/12C ratios are consistent with an expected preferential volatilization of 12C, rendering features in soil NOM 13C-enriched and some features in dust NOM 13C-depleted. Anthropogenic compounds tend to diverge most dramatically from atmospheric 13C/12C, generally toward 13C-depletion, but pesticides we tested tended toward 13C-enriched. This pattern is robust and evident in: i) anthropogenic vs natural features in dust; ii) perfluorinated compounds in standards and as soil contaminants; and iii) sunscreen compounds in commercial products and wastewater. Considering the observed wide 13C/12C range for anthropogenic compounds, we suggest Rayleigh distillation during synthetic processes commonly favors one isotope over the other, rendering a source reservoir that is progressively depleted as synthesis proceeds and, consequently, generates a wide variation in 13C/12C for man-made products. However, kinetic-isotopic effects and/or synthesis from petroleum/natural gas might contribute to the anthropogenic isotopic signature as well. Regardless of cause, 13C/12C can be used to cull HR/MS molecular features that are more likely to be of anthropogenic or non-biotic origin.

Marine colloids, agents of the self-cleansing capacity of aquatic systems: Historical perspective and new discoveries

Colloids in the ocean are mainly composed of natural organic matter (NOM), with trace amounts of metals, metalloids, radionuclides, pollutants, and variable amounts of anthropogenically produced engineered nanoparticles and nanoplastics. State-of-the-art sampling and instrumental techniques were required to unravel both size spectra and chemical composition.Chemical components of colloidal macromolecular organic matter (COM) include aquagenic substances (composed of microbially produced Exopolymeric Substances (EPS), gels, transparent exopolymer particles (TEP) and TEP precursors), and pedogenic substances (mostly humic and fulvic matter). COM can be bioavailable and biodegradable. EPS in aquatic systems can form flocs of Marine Snow (MS) or Marine Oil Snow (MOS). EPS is thus important in initiating and maintaining aggregation, flocculation, and sedimentation processes of particles and microorganisms that act also as sorbents of pollutants, a process that contributes in a major way to the ‘self-cleansing capacity’ of aquatic systems.COM contains a diverse array of functionalities which can make them good metal chelating agents, amphiphilic and surface active pH-sensitive and redox-active. Due to numerous electrostatic and hydrophobic interactions between different moieties and ligand groups within a macromolecule, equilibrium constants, Ki, will become distribution functions for most reactions rather than fixed constants, as is common for low molecular weight organic molecules.Colloidal pumping of trace substances bound to EPS and other reactive macromolecular NOM compounds is counteracting the prevailing pathway of degradation of the bulk macromolecular NOM. Due to strong sorption capabilities for stable and radioactive metal ions, particle- and colloid-reactive radionuclides are useful to trace particle and organic carbon fluxes in the ocean.Open research questions include the role of different mechanisms that affect size spectra and composition of EPS in response to changing conditions, the role of macromolecular organic carrier molecules of radioactive and other trace substances that are used as oceanographic tracers; the potential use of the protein/carbohydrate ratio as a predictor of colloid or particle stickiness, aggregation or emulsification processes, and the importance of reactive oxygen species (ROS) mediated polymerization reactions of proteins and other molecules, which are part of EPS, for MS and MOS formation.

Rotating Ring-Disk Electrode Study of the Electrochemical Dehalogenation of Iodinated Contrast Media

Iodinated contrast media (ICM) occur widely in the environment and are difficult to remove by conventional water treatment methods because of ICMs’ hydrophilicity and resistance to biodegradation. ICMs have also been shown to be precursors of toxic reaction products, notably iodine-containing trihalomethanes and haloacetic acids. This study examined the performance of an alternative method of ICM degradation, notably their electrochemical (EC) reduction. ICMs used in this study were exemplified by iopamidol and diatrizoate. The method of rotating ring-disc electrode (RRDE) was used to elucidate rates and mechanisms of the EC reactions of the selected ICMs. Experiments were carried at varying hydrodynamic conditions, concentrations of iopamidol, diatrizoate, natural organic matter (NOM) and model compounds (resorcinol, catechol, guaiacol) which were used to examine interactions between products of the EC reduction of ICMs and halogenation-active species. The data showed that iopamidol and diatrizoate were EC-reduced at potentials < -0.45 V vs. s.c.e. In the range of potentials -0.65 to -0.85 V their reduction was mass transfer-controlled. The presence of NOM and model compounds did not affect the EC reduction of iopamidol and diatrizoate but active iodine species formed as a result of the EC-induced transformations of these ICMs reacted readily with NOM and model compounds. These data provide more insight into the nature of generation of iodine-containing by-products in the case of reductive degradation of ICMs.

Electrochemical reductive dehalogenation of iodine-containing contrast agent pharmaceuticals: Examination of reactions of diatrizoate and iopamidol using the method of rotating ring-disc electrode (RRDE)

AbstractThis study examined the electrochemical (EC) reduction of iodinated contrast media (ICM) exemplified by iopamidol and diatrizoate. The method of rotating ring-disc electrode (RRDE) was used to elucidate rates and mechanisms of the EC reactions of the selected ICMs. Experiments were carried at varying hydrodynamic conditions, concentrations of iopamidol, diatrizoate, natural organic matter (NOM) and model compounds (resorcinol, catechol, guaiacol) which were used to examine interactions between products of the EC reduction of ICMs and halogenation-active species. The data showed that iopamidol and diatrizoate were EC-reduced at potentials < −0.45 V vs. s.c.e. In the range of potentials −0.65 to −0.85 V their reduction was mass transfer-controlled. The presence of NOM and model compounds did not affect the EC reduction of iopamidol and diatrizoate but active iodine species formed as a result of the EC-induced transformations of these ICMs reacted readily with NOM and model compounds. These data provide more insight into the nature of generation of iodine-containing by-products in the case of reductive degradation of ICMs.

Applying ultraviolet/persulfate (UV/PS) pre-oxidation for controlling ultrafiltration membrane fouling by natural organic matter (NOM) in surface water

Membrane fouling is a recognized obstacle for the application of ultrafiltration (UF) for drinking water treatment. In this study, ultraviolet/persulfate (UV/PS) oxidation was employed as a pretreatment to control membrane fouling caused by natural organic matter (NOM) in surface water. The effects of UV/PS pretreatment on amounts and characteristics of NOM were investigated in terms of dissolved organic carbon, fluorescent spectrum, molecular weight distribution and hydrophobicity. UF membrane fouling during filtration of raw and pre-oxidized water was compared with transmembrane pressure development, and the fouled membranes were further characterized using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results indicate that NOM was considerably degraded and partially mineralized (∼58%) by UV/PS pretreatment at a PS dose not exceeding 0.6 mM and a UV irradiation time within 120 min, which was attributed to the generation of sulfate and hydroxyl radicals. The fluorescent compounds in NOM were almost completely degraded (>98%) by the UV/PS pretreatment at a PS dose of 0.4 mM, except for tyrosine-like proteins (∼80%). Moreover, UV/PS pretreatment decreased the ratio of macromolecular compounds and increased the hydrophilic fractions, resulting in reduced NOM adhesion to the membrane. Hence, irreversible fouling by NOM was significantly retarded (∼75%) by the UV/PS pretreatment due to reduction in NOM, and more importantly by preferential degradation of fluorescent, macromolecular and hydrophobic compounds. Fouling control performance was considerably improved at increased PS doses and extended UV irradiation time.