Natural Organic Matter Components Research Articles

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.

Copper doped Fe-N-C as an excellent Fenton-like catalyst for membrane fouling mitigation against natural organic matters at neutral pH

The presence of humic substances as a component of natural organic matter (NOM) may cause inefficiency towards drinking water treatment processes, especially the membrane fouling during filtration process. Therefore, to enhance the efficiency of the conventional membrane filtration process, several copper doped Fe-N-C bimetallic heterogeneous Fenton-like catalysts (Cux@FeNC) were prepared and evaluated by executing their catalytic degradation performance against NOM. Results indicated that humic acid (HA, 10 mg/L) could be significantly degraded (95%) within 30 min application of Cu5p@FeNC-Fenton under neutral pH, which was relatively higher than of FeNC-Fenton (70%) under identical conditions. The macromolecular organic matters in NOM could be destroyed more effectively while the overall mineralization degree also became relatively higher. Meanwhile, a lower membrane fouling of UF (PES 20 kDa)/NF (DOW 270) and highest flux recovery after backwash were observed with Cu5p@FeNC-Fenton treatments. Characterization and chemical analysis further explored the introduction of Cux in FeNC was responsible for the rapid reactive oxygen species (ROS) generation and efficient degradation of NOM. Additionally, a possible copper-iron synergetic mechanism in Fenton-like system was proposed. This work gives a deep insight into the potential NOM degradation using Fenton-like Cux@FeNC catalysts and ensures the membrane fouling mitigation for effective water treatment processes.

Responses of hepatic biotransformation and antioxidant enzymes in Japanese medaka (Oryzias latipes) exposed to humic acid.

Humic substances, a major component of natural organic matter in surface waters, can induce biotransformation enzyme activities and influence antioxidant defense in fish. The study aimed to provide a molecular basis for the stress responses, the synthesis of biotransformation, and antioxidant enzymes in particular. Adult medaka fish (Hd-rR strain) were exposed to environmentally relevant concentrations of humic acid for 96h. The actual humic acid concentrations in water were determined photometrically and expressed as organic carbon concentrations. Liquid chromatography with tandem mass spectrometry was used for protein profile analysis of medaka liver samples. The relative amount of isozymes was determined using the label-free quantification approach. Hepatic biotransformation enzyme activities were measured as well. Thus, ethoxyresorufin-O-deethylase activity showed a pronounced induction at the highest tested concentration (9.4mg C/L). Various biotransformation and antioxidant isozymes responded to humic acid differently, reflecting a balanced interplay of proteins that ensures the metabolism of humic acid in fish liver. Some isozymes were not affected by humic acid. The study provides new insight into the molecular mechanisms of the fish stress response to the humic acid-related challenge.

Evaluation of membrane tailored with biocompatible halloysite‒polyaniline nanomaterial for efficient removal of carcinogenic disinfection by‒products precursor from water

Humic acid (HA) is the main component of natural organic matter that generates carcinogenic by‒products during disinfection and its removal from water resources is challenging. Biocompatible halloysite (HNTs) nanomaterial decorated with polyaniline (HNTs‒PANI) was synthesized via polymerization technique. HNTs‒PANI was added to prepare polyethersulfone mixed matrix membranes (MMMs). The influence of HNTs‒PANI concentration on HA removal efficiency was studied by varying the HNTs‒PANI (0.5, 1 and 1.5 wt%). The characterization studies of MMMs revealed that the addition of HNTs‒PANI improved the morphology of the membranes, surface properties, chemical stability and thermal property. The amine and hydroxyl groups within the MMMs improved the membrane wettability. The addition of HNTs‒PANI within the MMMs had significantly enhanced the pure water flux and HA filtration. YHP2 MMM with 1 wt% of HNTs‒PANI demonstrated sieving coefficient of 0.10 and the highest HA removal efficiency of 91% greater than the neat PES membrane. Furthermore, the antifouling property of the MMMs was studied using HA as foulant. 1 wt% of HNTs‒PANI added MMM showed a high flux recovery ratio (94.9%) with low total fouling of 12% and low irreversible fouling of 5%, respectively. Thus, HNTs‒PANI was an efficient nanomaterial for enhancing the pure water flux, removal efficiency and antifouling property to treat water contaminated with HA.

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.

Beneficial impacts of natural biopolymers during surface water purification by membrane nanofiltration

Membrane filtration in various forms has become an increasingly used treatment method worldwide for the supply of safe drinking water. The fouling of membranes is commonly considered to be the major operational limitation to its wider application since it leads to frequent backwashing and a shortening of membrane life, and increased production costs. The components of natural organic matter (NOM) in surface waters have been reported previously to be important foulants of nanofiltration (NF) membranes, however, the potential beneficial effect of particular components of these ‘foulants’ has not been investigated or demonstrated to date. In this study, we have considered the roles of different organic materials including autochthonous NOM (e.g., biopolymers) and allochthonous NOM (e.g., humic substances) on the fouling of NF membranes by bench-scale tests with samples of two representative source waters (UK) taken in two different seasons (autumn and winter). Microfiltration (MF) and ultrafiltration (UF) were employed to generate two permeates, between which the presence of biopolymers (30 kDa – 90 kDa) is the major difference. We developed sequential filtration (MF/UF-NF) to investigate biopolymers’ behaviours in NF process. The results showed that the accumulation of biopolymers on NF membranes can mitigate fouling by providing a protective layer in which medium-low molecular weight (MW) materials (e.g. humic substances) are separated by adsorption and/or size exclusion. The protective layers assisted by biopolymers were seen to be thicker under scanning electron microscope (SEM) observation and characterized by higher roughness (i.e. three-dimensional, spacial structure) and greater adsorptive capacity. Moreover, improvement on NF membrane fouling mitigation could be more significant in autumn, comparing to that in winter. The findings in this study were found to be repeatable in similar tests with samples of comparable raw waters in China, and will be important to the practical application of NF membrane systems in terms of a new approach to combating fouling in long-term operation.

Refractory Humic-like Substances: Tracking Environmental Impacts of Anthropogenic Groundwater Recharge.

To unravel the crucial components of natural organic matter that respond to the process of anthropogenic groundwater recharge (AGR) from different recharge water sources, dissolved organic matter (DOM) and base-extractable particulate organic matter (POM) in groundwater and surface water were analyzed using excitation-emission matrix spectroscopy coupled with parallel factor analysis (EEM-PARAFAC). The EEM and traditional spectral indices of samples show that the fluorescent intensity, molecular weight, and humification degree of the DOM were relatively higher than those of the POM, and the groundwater in the reclaimed water recharge area (RWRA) was more contaminated than in the south-to-north water recharge area (SNWRA). PARAFAC analysis indicates that the DOM was dominated by an allochthonous humic-like substance (C1), whereas the POM was dominated by tryptophan-like substances associated with microbial activity (C2). Partitioning of PARAFAC components between DOM and POM showed that the humic-like substances (C1 and C4) were more likely to be distributed into a dissolved phase compared to the protein-like substances (C2 and C3), which suggested the potential use of C1 and C4 as a tracking indicator. In particular, the clear gradient distributions along both the hydrogeological profile and different aquifer systems in terms of the concentration and composition of C1 also discriminated between the RWRA and SNWRA with regard to the effects of various AGRs on the groundwater. The association between C1 and water-quality indicators revealed by principal component analysis further indicated that refractory humic-like substances would track the environmental impacts of intentional AGR processes.

A Mechanistic Exploration of Natural Organic Matter Aggregation and Surface Complexation in Smectite Mesopores

Soil minerals and organic matter play critical roles in nutrient cycling and other life-essential biogeochemical processes, yet the structural and dynamical details of natural organic matter (NOM) film formation on smectites are not fully understood on the molecular scale. XRD of Suwannee River NOM-hectorite (a smectite clay) complexes shows that the humic and fulvic components of NOM bind predominantly at the external surfaces of packets of smectite platelets rather than in the interlayer slit pores, suggesting that the key behavior governing smectite-NOM interactions takes place in mesopores between smectite particles. New molecular dynamics modeling of a ∼110 Å H2O-saturated smectite mesopore at near-neutral pH shows that model NOM molecules initially form small clusters of 2-3 NOM molecules near the center of the pore fluid. Formation of these clusters is driven by the hydrophobic mechanism, where aromatic/aliphatic regions associate with one another to minimize their interactions with H2O, and charge-balancing cations associated with the deprotonated carboxylate sites are located only at the outer surface of these clusters. Despite hydrophobicity driving the initial clustering, NOM clusters are formed more quickly when high-charge-density cations like Ca2+ are present vs low-charge-density cations like Cs+, as the former cations more effectively minimize the electrostatic repulsions between the negatively charged NOM molecules. Once the small hydrophobicity-driven NOM clusters form, the simulations show that Ca2+ promotes the aggregation of NOM clusters through tetradentate Ca2+ bridges involving carboxylate groups on two different NOM clusters. Importantly, our studies indicate that Ca2+ plays a crucial role in binding the NOM clusters to the smectite surface, which occurs through multiple quaternary complexes (Ob)-H2O-Ca2+-COO-NOM. In contrast, Cs+ never forms any coordination or acts like bridges between NOM molecules nor as ion bridges to the smectite surface. Additionally, we observe the formation of a metastable superaggregate involving all 16 NOM molecules several times in a Ca2+-bearing mesopore fluid. Superaggregates are never observed in the simulations involving Cs+. The modeling results are fully consistent with helium ion microscope images of NOM-hectorite complexes suggesting that NOM surface films develop when preformed NOM clusters interact with smectite surfaces. Overall, the binding of NOM clusters to the outer surfaces of smectite particles and the formation of large NOM aggregates at neutral pH occur through cation bridging, and cation bridging only occurs when high-charge-density cations like Ca2+ are present.

STATISTICAL APPROACH TO ESTIMATING REGIONAL BACKGROUND CONCENTRATIONS OF PETROLEUM HYDROCARBONS IN SEDIMENTS

Modern approaches to environmental regulation require that regional background concentrations of pollutants in environmental objects are set to serve as the basis for an objective assessment of the geoecological situation at a certain spatial level using monitoring data. The determination of the regional background levels of pollutants in sediments is particularly relevant due to the lack of matching sanitary standards for their permissible concentrations in the Russian Federation. Petroleum hydrocarbons, being structural components of natural organic matter, enter water bodies also from anthropogenic sources. Their accumulation in sediments leads to secondary water pollution and alteration of the structural and functional characteristics of the aquatic ecosystems. The natural component of petroleum hydrocarbons must be taken into account when determining their background levels in sediments. Based on representative material and using a statistical approach, the background concentrations of petroleum hydrocarbons in sediments of rivers, storage reservoirs and lakes of the Republic of Tatarstan were calculated. The structure of the variability in the content of petroleum hydrocarbons in the sediments is represented by the ratio of three factors: the hydrological conditions, organic matter content, and the particle size distribution (the pelite fraction content) of the sediments. The baseline value of the background concentration of petroleum hydrocarbons in sediments of water bodies in the Republic of Tatarstan is the median of the series, and its upper quartile serves as the criterion telling whether the value is within the regional background. Minimal background concentrations of petroleum hydrocarbons – 45 to 180 mg/kg (the upper limit of 100‒475 mg/kg) – are typically found in the sediments of rivers and storage reservoirs. In lake sediments, where the proportion of organic matter and clay particles is higher due to hydrological and production characteristics, the background content of petroleum hydrocarbons is estimated to be much higher – 90‒320 mg/kg, and the upper limits of the background content are 195‒510 mg/kg.

A feasible strategy to improve confident elemental composition determination of compounds in complex organic mixture such as natural organic matter by FTICR-MS without internal calibration

Confident elemental composition determination of compounds in complex samples such as natural organic matter (NOM) by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is challenging due to the interference between multiple components in these samples during detection. Here the performance of Solarix 15T-FTICR-MS in terms of accurate relative natural isotope abundance (RIA) and mass measurements for elemental composition determination of compounds in complex samples such as NOM was systematically evaluated. The optimal sweep excitation power values ranging from 20% to 22% was found to significantly diminish the underestimation of RIA measurement for 13C1 peaks of NOM components by FTICR-MS. Random error was found to be one of the main sources for the RIA errors of 13C1 peaks with S/N ratios <25. The mean averaged RIA errors of less than 10% could be obtained by averaging the measured RIAs of each 13C1 peaks in five replicated runs. By adjusting the total ion abundance of NOM complex sample between 3.8-E7 and 1.4-E8 which was simultaneously similar to that of external calibrant during detection, mass errors of lower than 1 ppm for NOM components with m/z lower than 700 Da could be obtained without internal calibration. Meanwhile, a linear correlation between mass errors of ions in NOM complex sample and their m/z values could be obtained. The mass error deviation derived from the linearity was firstly used as new criterion to reduce the number of false formula candidates. A novel strategy of combination of high mass accuracy, high spectral accuracy, and mass error deviation for elemental composition determination of unknown compounds in complex sample such as NOM by FTICR-MS was proposed and applied for different complex samples. Compared to the traditional method, about one fold increasement in the number of the unique formula assignments for measured ions was obtained by using our strategy.

Facet-Dependent Adsorption and Fractionation of Natural Organic Matter on Crystalline Metal Oxide Nanoparticles.

Natural organic matter (NOM) and crystalline metal oxide nanoparticles are both prevalent in natural aquatic environments, and their interactions have important environmental and biogeochemical implications. Here, we show that these interactions are significantly affected by an intrinsic property of metal oxide nanocrystals, the exposed facets. Both anatase (TiO2) and hematite (α-Fe2O3) nanocrystals, representing common engineered and naturally occurring metal oxides, exhibited apparent facet-dependent adsorption of humic acid and fulvic acid. This facet-dependent binding was primarily driven by surface complexation between the NOM carboxyl groups and surficial metal atoms. Thus, the adsorption affinity of different-faceted nanocrystals was determined by the atomic arrangements of crystal facets that controlled the activity of metal atoms and, consequently, the ligand exchange and binding configuration of the carboxyl groups in the first hydration shell of nanocrystals. Distinct facet-dependent fractionation patterns were observed during adsorption of NOM components, particularly the low-molecular-weight and photorefractory constituents. The molecular fractionation of NOM between water and metal oxide nanoparticles was dictated by the combined effects of facet-dependent metal complexation, hydrophobic interaction, and steric hindrance and may significantly influence the NOM-driven processes occurring both in aqueous phases and at water-nanoparticle interfaces.

Pretreatment for water reuse using fluidized bed crystallization

This research investigated the use of fluidized bed crystallization for removing scale forming species and natural organic matter (NOM) from treated municipal wastewater prior to water reclamation. The effect of pH on Ca2+, Mg2+, silica and NOM removal in a fluidized bed crystallization reactor (FBCR) was determined. NOM removal in the FBCR was compared to that for the conventional treatments, ultrafiltration and ferric chloride coagulation/flocculation. Under optimized conditions, fluidized bed crystallization was able to remove more than 99.9 % of Mg2+, 97 % of Ca2+ and 42 % of silica. The FBCR was also able to remove 25 % of NOM, which was intermediate between NOM removal by ferric chloride (56 %) and ultrafiltration (13 %). Size exclusion chromatography-organic carbon detection (SEC−OCD) indicated that the majority of NOM removal occurred via co-precipitation with Mg(OH)2. Excitation emission matrix-parallel factor (EEM-PARAFAC) analysis was used to investigate the types of NOM removed. The FBCR was able to remove all five NOM components (three humic acids, one fulvic acid and one protein-like substance), including 100 % of the autochthonous fulvic acids. Ferric chloride was also able to remove all five NOM components, but only one third of the autochthonous fulvic acids, while ultrafiltration was able to remove only 11 % of the protein-like NOM.

Investigating the fate of natural organic matter at a drinking water treatment plant in South Africa using optical spectroscopy and chemometric analysis

The removal dynamics of biodegradable dissolved organic carbon (BDOC) and natural organic matter (NOM) polarity fractions at a water treatment plant (WTP) in South Africa was studied using UV-Vis absorbance, fluorescence excitation-emission matrix, and two-dimensional synchronous fluorescence spectroscopy (SFS). This study gave insights into the transformation of NOM due to treatment processes. The objectives of the study were: (i) to use chemometric analysis and two-dimensional SFS correlations to investigate the evolution of NOM arising from treatment processes, and (ii) to access the chemical profile dynamics of polarity and BDOC fractions throughout the treatment train. The UV254 absorbance, which indicates aromaticity, reduced by 45% along the WTP. Gaussian fitting of UV-Vis data showed a decreasing trend in intensity and number of bands along the treatment process. The removal efficiency of NOM components followed the order: humic-like (HL) &gt; tyrosine-like (TYL) &gt; fulvic-like (FL) &gt; tryptophan-like (TPL) &gt; microbial-like (MBL). At the source, the relative distribution of the hydrophobic (HPO), hydrophilic (HPI), and transphilic (TPI) fractions was 45%, 31%, and 24%, respectively. The HPI was recalcitrant to treatment, and the TYL component of the HPI fraction was conjectured to be a disinfection byproduct limiting reagent. The HL and FL components of the BDOC fraction were the major substrates for bacterial growth. According to two-dimensional-SFS correlation, TYL, TPL, and MBL varied concurrently across the treatment stages. Used for the first time in South Africa, the robustness of a multi-dimensional approach of optical methods coupled with chemometric tools for the assessment of the fate of NOM along the treatment processes was revealed by this study.

Effects of hydrophobicity-based fractions of Pony Lake fulvic acid on the colloidal stability and dissolution of oppositely charged surface-coated silver nanoparticles

Environmental contextThe fate of silver nanoparticles (AgNPs) in aqueous systems could be influenced by the hydrophobicity of natural organic matter. We observed that the aggregation and dissolution of oppositely charged AgNPs were controlled by the selectivity and dynamics of sorption processes involving the nanoparticle surface and hydrophobic groups on natural organic matter. These findings will be helpful to understand the fate and effects of coated AgNPs in natural systems. AbstractThe fate of silver nanoparticles (AgNPs) released into aquatic environments is significantly affected by natural organic matter (NOM). However, current studies are still insufficient to understand interactions between NOM and AgNPs because they do not explicitly consider the heterogeneity of NOM. We investigated how NOM components with different properties (hydrophobicity, molecular weight, aromaticity, and polarity of functional groups) interact with AgNPs coated with citrate (Cit) and branched polyethylenimine (BPEI) and influence their colloidal stability and dissolution. Pony Lake fulvic acid (PLFA) selected as a model NOM was fractionated into hydrophobic (HPO) and transphilic (TPI) fractions. Sorption of PLFA molecules with a high content of polar functional groups bound to the aromatic rings onto nanoparticles was more favourable in the case of the TPI fraction, which most likely resulted in higher aggregation for both AgNPs and stronger protection of BPEI-AgNPs against dissolution compared with the HPO fraction. Additionally, in contrast to the Cit-AgNPs, resorption of Ag+ ions released from BPEI-AgNPs and/or sorption of Ag+-PLFA complexes to the nanoparticles was most likely a dynamic process, as suggested by the time-dependent changes in the molecular weight of the PLFA fractions sorbed to the BPEI-AgNP surface. These observations suggest that the accessibility of the AgNP surface for the hydrophobicity-based fractions of NOM as well as their colloidal stability and dissolution are controlled by the type and charge of coating materials and by the molecular weight, aromaticity, and content of polar functional groups of NOM.

Effect of dissociation constant (pKa) of natural organic matter on photo-generation of reactive oxygen species (ROS)

Natural organic matter (NOM) contains a large number of aromatic ketones and quinones, which can produce reactive oxygen species (ROS), such as 1O2 and HO·, through photosensitization. These ROS play important roles in the attenuation of organic pollutants in sunlit surface water. The NOM components fractionated with XAD-8 resin at different pH influence the photo-generation of ROS, which may be related to the degree of dissociation of functional groups. In this study, probe chemicals were used to investigate the effect of dissociation degree (pKa) of NOM model compounds on ROS production under 254 nm UV irradiation. Experimental results showed that six model compounds with similar molecular weights and structures but different pKa values have different ROS production abilities in a pH 7.0 reaction system. The ability for DHB2,5 (2.97), DHB3,4 (4.48), and GUA (9.99) to photo-generate 1O2 increased with increasing dissociation. The ability for DHB3,4 and GUA to photo-generate HO· followed the same trend. The correlation between NOM dissociation constant and ROS generation is preliminary established, which explains the influence of functional groups. Our results may provide some basic information for understanding the correlation between NOM structural features and ROS generation.

Polyethyleneimine modification of activated fly ash and biochar for enhanced removal of natural organic matter from water via adsorption.

In this study, fly ash (FA) and biochar (BC), two common industrial byproducts, were activated and surface-modified with polyethyleneimine (PEI) to enhance their capacities to remove natural organic matter (NOM) from water via adsorption. Different fluorescent components were identified using fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) to explore the individual adsorption behaviors of different organic constituents in a bulk NOM. The NOM adsorption was quantitatively examined via adsorption isotherm and kinetics models. Compared to the pristine adsorbents, the functionalized adsorbent with increased surface area and positive surface charge achieved higher NOM adsorption. By evaluating the adsorptive behaviors of UV-absorbing and fluorescent moieties, it was concluded that the operative mechanism of adsorption included electrostatic attraction, hydrogen bonding, and π-π interaction. At the optimal pH of 3, the surface-modified FA and BC (i.e., FA-PEI and BC-PEI) had adsorption capacities for NOM that were ∼3 times higher than the capacities of the pristine materials. Due to its aromatic features, π-π interaction may have enhanced BC and BC-PEI selective adsorption of aromatic NOM components compared to FA and FA-PEI. Kinetic modelling showed that the mesopores of FA-PEI were available for NOM adsorption and diffusion of NOM molecules into the mesoporous structures was rate-limiting. On the other hand, PEI-modification may have further reduced NOM diffusion through the narrow micropores in BC such that external adsorption primarily occurred on BC-PEI. The modified adsorbents showed a faster adsorption kinetics than the pristine counterparts and a high durability in repeated adsorption-desorption cycles.

Effects of Sorption on Redox Properties of Natural Organic Matter.

Natural organic matter (NOM) is an important redox-active component of natural porous media and predominantly occurs in the sorbed state. Nevertheless, the effects of NOM sorption at minerals on its redox properties are unknown and thus are the major objective of this study. We report how adsorption of three different humic acids (HAs) to redox-inert sorbents (polar Al2O3 and nonpolar DAX-8 resin) affects their electron-exchange capacities (EEC) and redox states. The electron-donating capacity of HAs sorbed at Al2O3 increased by up to 200%, whereas the EEC of the remaining dissolved HA fractions decreased compared with their initial properties. Sorption at DAX-8, however, did not affect significantly the EEC of HAs. We rationalize these results by (i) preferential sorption of NOM components rich in redox-active groups (e.g., quinone, polyphenols) and (ii) surface-catalyzed polymerization of polyphenolic compounds. Our results demonstrate that even in the absence of electron exchange with the sorbent, adsorption to polar mineral surfaces considerably affects the redox properties of NOM. Quantification of the redox state and EEC of adsorbed NOM is thus crucial for assessing electron-transfer processes as well as organic carbon stabilization and sequestration in soils and sediments.

Using UV/H2O2 pre-oxidation combined with an optimised disinfection scenario to control CX3R-type disinfection by-product formation

The effects of UV/H2O2 pre-oxidation or disinfection methods on the formation of partial disinfection by-products (DBPs) have been studied previously. This study assessed the effect of UV/H2O2 pre-oxidation combined with optimisation of the disinfection method on the formation of six classes of CX3R-type DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetaldehydes (HALs), haloacetonitriles (HANs), halonitromethanes (HNMs), and haloacetamides (HAMs). Experimental results showed that a simulated distribution system (SDS) in-situ chloramination or pre-chlorination followed by chloramination effectively decreased total CX3R-type DBP formation by 51.1–63.5% compared to SDS chlorination, but little reduction in DBP-associated toxicity was observed. The dominant contributors to the calculated toxicity were HANs and HALs. UV/H2O2 pre-oxidation was able to destroy the aromatic and dissolved organic nitrogen components of natural organic matter. As a consequence, THM, HAA, and HAL formations increased by 49.5–55.0%, 47.8–61.9%, and 42.0–67.1%, respectively, whereas HAN, HNM, and HAM formations significantly decreased by 52.1–83.6%, 42.9–87.3%, and 74.1–100.0%. UV/H2O2 pre-oxidation increased total CX3R-type DBP formation, during SDS chlorination, whereas SDS in-situ chloramination or pre-chlorination followed by chloramination of UV/H2O2-treated water produced lower total CX3R-type DBPs than water without UV/H2O2 pre-oxidation. Nevertheless, the DBP-associated toxicity of water with UV/H2O2 pre-oxidation was substantially lower than the toxicity for water without UV/H2O2 pre-oxidation, decreased by 24.1–82.7%. HALs followed by HANs contribute to major toxic potencies in UV/H2O2 treated water. The best DBP concentration and DBP-associated toxicity abatement results were achieved for water treated by UV/H2O2 coupled with in-situ chloramination treatment.

Terrestrial-marine continuum of sedimentary natural organic matter in a mid-latitude estuarine system

Humic acids (HA) have several environmental roles, but are particularly important in aquatic environments, being recognized as redox active natural organic matter (NOM) components. We examined NOM in recent sediments of a low-energy coastal environment which is free from inputs of dissolved terrestrial HA as their solubility is suppressed by bonding with Ca2+ ions. Our aim is to investigate the contribution of autochthonous versus terrestrial C sources to HA and their fractions along a river-coastal lagoon transect. Surface sediments were collected along the Aussa River (R), in the central basin of the Marano and Grado Lagoon (L) and within a secluded lagoon fish farm (FF). Extractable NOM components were obtained by extracting sediments first with 0.5 M NaOH (free NOM) and then with 0.1 M NaOH plus 0.1 M Na4P2O7 (bound NOM). Extracts were separated into non-humic and humic fractions by solid phase chromatography. Organic carbon (Corg), total nitrogen (Ntot), δ13C, and δ15N were determined with an Isotope Ratio Mass Spectrometer (Thermo Scientific Delta V Advantage) coupled with an Elemental Analyzer (Costech Instruments Elemental Combustion System). Fourier-transform infrared (FTIR) spectra were recorded with a FT-IR100 PerkinElmer Spectrometer. UV-vis spectra were recorded at pH 7 by a Varian Cary Spectrophotometer. Both NOM and HA display typical traits of terrestrial origin in river sediments and of a more marine (algal) origin in lagoon and fish farm sediments. This trend is evident in free HA, whereas bound HA seem more influenced by terrestrial inputs. A larger proportion (60–70%) of non-humic C was extracted by NaOH in all samples. Bound HA differ from free HA for their C/N ratios, which are higher and vary within a much narrower range. The changes in HA’s 13C isotopic composition, FTIR spectra, and spectroscopic parameters (SUVA254, SR, and aromaticity) highlight a progressive mixing of terrestrial and marine substrates that either undergo in situ humification or are transported as materials sorbed onto suspended mineral particles. Our results highlight the existence of a complex, but continuous pattern of terrestrial and marine contributions to C sequestration and humification even in transitional environments where allochthonous humic C inputs are restricted due to insolubilization of humic substances by Ca2+. Along the examined transect, the NOM and free and bound HA appear well differentiated. Terrestrial inputs contribute to the bound HA fraction via transported mineral particles in all the samples, no matter the environment encountered.

Reactive Nitrogen Species Are Also Involved in the Transformation of Micropollutants by the UV/Monochloramine Process.

The UV/monochloramine (NH2Cl) process is an emerging advanced oxidation process (AOP) in water treatment via radicals produced from the UV photolysis of NH2Cl. This study investigated the degradation of micropollutants by the UV/NH2Cl AOP, with ibuprofen (IBP) and naproxen (NPX) selected as representative micropollutants. Hydroxyl radical (HO•) and chlorine atom (Cl•) were identified in the process, and unexpectedly, we found that reactive nitrogen species (RNS) also played important roles in the transformation of micropollutants. The electron paramagnetic resonance (EPR) analysis proved the production of •NO as well as HO•. The concentrations of HO•, Cl•, and •NO in UV/NH2Cl remained constant at pH 6.0-8.6, resulting in the slightly changed UV fluence-based pseudo-first-order rate constants (k') of IBP and NPX, which were about 1.65 × 10-3 and 2.54 × 10-3 cm2/mJ, respectively. For IBP, the relative contribution of RNS to k' was 27.8% at pH 7 and 50 μM NH2Cl, which was higher than that of Cl• (6.5%) but lower than that of HO• (58.7%). For NPX, the relative contribution of RNS to k' was 13.6%, which was lower than both Cl• (23.2%) and HO• (46.9%). The concentrations of HO•, Cl•, and •NO increased with the increasing NH2Cl dosage. Water matrix components of natural organic matter (NOM) and bicarbonate can scavenge HO•, Cl•, and RNS. The presence of 5 mg/L NOM decreased the k' of IBP and NPX by 66.9 and 57.6%, respectively, while 2 mM bicarbonate decreased the k' of IBP by 57.4% but increased the k' of NPX by 10.5% due to the contribution of CO3•- to NPX degradation. Products containing nitroso-, hydroxyl-, and chlorine-groups were detected during the degradation of IBP and NPX by UV/NH2Cl, indicating the role of nitrogen oxide radical (•NO) as well as HO• and Cl•. Trichloronitromethane formation was strongly enhanced in the UV/NH2Cl-treated samples, further indicating the important roles of RNS in this process. This study first demonstrates the involvement of RNS in the transformation of micropollutants in UV/NH2Cl.