Types Of Natural Organic Matter Research Articles

Influence of natural organic matter on the aggregation dynamics of biochar colloids derived from various feedstocks

Abundant biochar colloids (BCs) produced from a wide range of feedstocks, resulting from forest fires, agricultural production, and environmental restoration, exhibit varying aggregation behaviors influenced by feedstock type and natural organic matter. However, the impact of natural organic matter on the colloidal stability of BCs derived from different feedstocks remains poorly understood. In this study, six selected biochars were derived from various feedstocks as follows: sewage sludge (SS), rice husk (RH), oil seed rape straw pellets (OSR), wheat straw pellets (WS), miscanthus straw pellets (MS) and softwood pellets (SW). The colloidal stability of BCs, with the exogenous addition of organic matter, was further determined. The order of critical coagulation concentrations (CCCs) of BCs with the presence of humic acid (HA) was as follows: RH (989.48 mM) < MS (1084.69 mM) < SS (1149.76 mM) < WS (1338.99 mM) < OSR (2402.98 mM) < SW (3151.32 mM). This order was significantly positively correlated with the specific surface area and negatively correlated with the ash content of the bulk biochar. Compared to HA, bovine serum albumin (BSA) more effectively inhibited the aggregation behavior of BCs due to steric hindrance. The initial aggregation rate constant (k) of BCs at 3000 mM NaCl was as follows: MS (0.238 nm/s) > OSR (0.142 nm/s) > WS (0.128 nm/s) > SS (0.126 nm/s) > RH (0.118 nm/s) > SW (0.112 nm/s). The stabilizing effects of BSA on biochar colloids were independent of the physicochemical properties of bulk biochar. In the presence of BSA, a thin layer of protein corona significantly enhanced the stability of biochar colloids, particularly the BCs derived from MS. Our results underscore the importance of considering feedstock resources and natural organic matter type when assessing the aggregation and potential risks of BCs in aquatic systems.

Elucidating the conformation effects within adsorption of natural organic matter on mesoporous graphitic carbon

The conformation effects were frequently reported to affect the adsorption of natural organic matter (NOM), but such a specific mechanism is poorly understood. To address this knowledge gap, based on the adsorption of NOM on mesoporous graphitic carbon nitride (MCN) prepared via a novel pseudo-templating method, the conformation effects were elucidated. The results showed that MCNs nano-architectures with uniform mesopores were successfully fabricated and showed prominent adsorption capacity. The maximum adsorption amounts of MCN-0.5 for fulvic acid (FA) and leonardite humic acid (HA) were 73.61 mgC g−1 and 135.57 mgC g−1, respectively. The adsorptive affinities of components for HA and Elliott soil HA (ESHA) were related to structural condensation; the components with the more coiled conformation exhibited higher affinities because of occupying less active sites and weakening the electrostatic repulsion. Such conformation effects were further established with respect to NOM types and components, as well as solution chemistry. HA and ESHA suffered from variations from the coiled to linear conformations as pH increased, but not the other four types of NOM tested, and particularly the humic-like and territorial humic-like components were critical in such conformational variations. The adsorption of HA and ESHA was affected by pH via both the conformation effects and the interaction mechanism. By contrast, the conformation of six types of NOM was not affected by the common cations (Na+, K+, Mg2+, Ca2+), and these cations impacted NOM adsorption only through the conventional interactions.

Bacterial inactivation in sunlit surface waters is dominated by reactive species that emanate from the synergy between light, iron, and natural organic matter

In this study, the synergistic and antagonistic effects of Fe species and coexisting natural organic matter (NOM) on the efficacy of solar light disinfection of water are investigated. Different initial iron species (Fe2+/Fe3+) and naturalorganic matter types (Suwannee River-SRNOM, Nordic Reservoir NOM-NDNOM, SR Humic Acid-SRHA, and SR Fulvic Acid-SRFA) were selected. The bactericidal actions of Fe and NOM, alone or in conjunction, were evaluated at various initial iron dosing concentrations, NOM concentrations, irradiation intensities, and pH values. We show that when an appropriate iron (1 ppm Fe2+ or 0.25 ppm Fe3+) and NOM concentration (2 ppm SRNOM or 5 ppm NDNOM) coexisted, synergistic inactivation was observed in the pH range 5.0–8.0. A plausible explanation is that the presence of Fe+NOM significantly promoted the generation of hydroxyl radicals (•OH) and singlet oxygen (1O2), which led to enhanced disinfection rates. These results elucidate the previously understudied effects of ubiquitous elements in natural waters and their impact on solar-mediated bacterial inactivation.

Colloid-bound radicals formed in NOM-enhanced Fe(III)/peroxymonosulfate process accelerate the degradation of trace organic contaminants in water

The omnipresence of natural organic matter (NOM) in water bodies traditionally hinders the degradation of trace organic contaminants (TrOCs) in peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs). This study elucidates the positive role of NOM in enhancing the degradation of TrOCs through the Fe(III)/PMS process. During this process, NOM reduces Fe(III), yielding semiquinone-like radical (NOM•) and concurrently forming NOM-Fe(III) colloids. In addition to the Fe(II)-mediated activation pathway, Fe(III) sites on NOM-Fe(III) colloids effectively transfer electrons from NOM• or some redox-active moieties to PMS, resulting in the generation of long-lived colloid-bound SO4•−, which can readily undergo hydrolysis to produce HO•. The stabilization of SO4•− and HO• by NOM-Fe(III) colloids, combined with their moderate adsorption of TrOCs, results in surface-confined reactions that significantly enhance TrOC removal, despite the presence of concurrent quenching reactions between radicals and NOM. Further, the significant positive correlation between the phenolic contents of eight NOM types and TrOC degradation kinetics suggests phenolic moieties as the primary electron source for PMS activation. By in-situ utilizing NOM in raw water, a PMS-amended iron coagulation process with 0.2 mM Fe(III) and PMS effectively removes 90–100 % of six coexisting TrOCs. This study unveils the previously unrecognized role of colloid-bound radicals in decontamination processes, offering valuable insights into harnessing NOM's influence in advanced oxidation water treatment processes.

In-depth study of the removal of Mn(II) by Fe(VI) treatment and the profound influence of NOM on floc formation and properties

The presence of manganese(II) in drinking water sources poses a significant treatment difficulty for water utilities, thus necessitating the development of effective removal strategies. Treatment by Fe(VI), a combined oxidant and coagulant, has been identified as a potential green solution; however, its effectiveness is hampered by natural organic matter (NOM), and this underlying mechanism is not fully understood. Here, we investigated the inhibitory effect of three different types of NOM, representing terrestrial, aquatic, and microbial origins, on Mn(II) removal and floc growth during Fe(VI) coagulation. Results revealed that Fe(VI) coagulation effectively removes Mn(II), but NOM could inhibit its effectiveness by competing in oxidation reactions, forming NOM-Fe complexes, and altering floc aggregation. Humic acid was found to exhibit the strongest inhibition due to its unsaturated heterocyclic species that strongly bond to flocs and react with Fe(VI). For the first time, this study has presented a comprehensive elucidation of the atomic-level structure of Fe(VI) hydrolysis products by employing Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). Results demonstrated that NOM strengthened single-corner and double-corner coordination between FeO6 octahedrons that were consumed by Mn(II), resulting in an increased contribution of γ-FeOOH in the core-shell structure (γ-FeOOH shell and γ-F2O3 core), thereby inhibiting coagulation effects. Furthermore, NOM impeded the formation of stable manganite, resulting in more low-valence Mn(III) being incorporated in the form of an unstable intermediate. These findings provide a deeper understanding of the complex interplay between Fe coagulants, heavy metal pollution, and NOM in water treatment and offer insight into the limitations of Fe(VI) in practical applications.

Evaluation of diffusion coefficients as surrogate indicators for electrostatic repulsion in ultrafiltration membrane fouling

Impacted by the electrostatic repulsion between ultrafiltration (UF) membranes and natural organic matter (NOM), organic fouling precipitates significant operational difficulties in water treatment facilities. This study investigated the applicability of diffusion coefficients as surrogate indicators to evaluate the electrostatic repulsive forces between NOMs and UF membrane surfaces. We utilized three distinct types of NOMs and three different UF membranes, each possessing different charge characteristics. Notably, we found that the reduction in diffusion coefficients was markedly pronounced when membranes rich in ionizable functional groups with strong negative charges were involved, indicating heightened electrostatic repulsion. To confirm the reliability of diffusion coefficient reduction as a surrogate indicator of the electrostatic repulsive force, a comprehensive membrane fouling test was conducted. The results revealed a strong correlation between the two parameters, enhancing our understanding of the intricate dynamics of membrane fouling (R2 = 0.9744–0.9907). Thus, this study proposes the concept of utilizing the reduction in the diffusion coefficient as a surrogate indicator to represent the electrostatic repulsive force between NOMs and the UF membrane surface. This innovative approach contributes to enables proactive and predictive assessments of membrane performance, fostering a shift toward proactive maintenance and enhances the operational efficiency of water treatment facilities.

Photocatalytic Degradation of Humic Acid Using Bentonite@Fe3O4@ZnO Magnetic Nanocomposite: An Investigation of the Characterization of the Photocatalyst, Degradation Pathway, and Modeling by Solver Plugin

Humic acid (HA), the most highly prevalent type of natural organic matter (NOM), plays an effective role in the generation of disinfectant byproducts such as trihalomethanes and haloacetic acid, which are well known to be definitive carcinogens. Therefore, the proactive elimination of HA from water and wastewater is a crucial means of preventing this pollutant from reacting with the chlorine incorporated during the disinfection process. This study investigated the UV light photocatalytic elimination of HA, employing a bentonite@Fe3O4@ZnO (BNTN@Fe3O4@ZnO) magnetic nanocomposite. The most significant variables pertinent to the photocatalytic degradation process examined in this work included the pH (3–11), nanocomposite dose (0.005–0.1 g/L), reaction time (5–180 min), and HA concentration (2–15 mg/L). The synthesized materials were characterized via field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD), energy-dispersive X-ray spectroscopy (EDX), and vibrating-sample magnetometer (VSM) techniques, all of which revealed outstanding catalytic properties for the BNTN@Fe3O4@ZnO. The conditions under which greater efficiency was achieved included a pH of 3, a nanocomposite dose of 0.01 g/L, and an HA concentration of 10 mg/L. Under these conditions, in just 90 min of photocatalytic reaction, an HA degradation efficiency of 100% was achieved. From the modeling study of the kinetic data, the Langmuir–Hinshelwood model showed good compliance (R2 = 0.97) with the empirical data and predicted values. Thus, it can be concluded that the BNTN@Fe3O4@ZnO catalyst acts very efficiently in the HA removal process under a variety of treatment conditions.

Enhanced Oxidation of Antibiotics by Ferrate Mediated with Natural Organic Matter: Role of Phenolic Moieties.

The increasing presence of antibiotics in water sources threatens public health and ecosystems. Various treatments have been previously applied to degrade antibiotics, yet their efficiency is commonly hindered by the presence of natural organic matter (NOM) in water. On the contrary, we show here that nine types of NOM and NOM model compounds improved the removal of trimethoprim and sulfamethoxazole by ferrate(VI) (FeVIO42-, Fe(VI)) under mild alkaline conditions. This is probably associated with the presence of phenolic moieties in NOMs, as suggested by first-order kinetics using NOM, phenol, and hydroquinone. Electron paramagnetic resonance reveals that NOM radicals are generated within milliseconds in the Fe(VI)-NOM system via single-electron transfer from NOM to Fe(VI) with the formation of Fe(V). The dominance of the Fe(V) reaction with antibiotics resulted in their enhanced removal despite concurrent reactions between Fe(V) and NOM moieties, the radicals, and water. Kinetic modeling considering Fe(V) explains the enhanced kinetics of antibiotics abatement at low phenol concentrations. Experiments with humic and fulvic acids of lake and river waters show similar results, thus supporting the enhanced abatement of antibiotics in real water situations.

Reciprocal effects of NOM and solution electrolyte ions on aggregation of ferrihydrite nanoparticles

The effects of natural organic matter (NOM) types and electrolyte ions are crucial to the aggregation of ferrihydrite nanoparticles (Fh NPs) in the environment. Dynamic light scattering (DLS) was employed for the aggregation kinetics of Fh NPs (10 mg/L as Fe) in the present study. The critical coagulation concentration (CCC) values of Fh NPs aggregation in NaCl were obtained in the presence of 15 mg C/L NOM as SRHA (857.4 mM) > PPHA (752.3 mM) > SRFA > (420.1 mM) > ESHA (141.0 mM) > NOM-free (125.3 mM), indicating Fh NPs aggregation was inhibited as the above order. Comparatively in CaCl2, the CCC values were measured in ESHA (0.9 mM), PPHA (2.7 mM), SRFA (3.6 mM), SRHA (5.9 mM), NOM-free (76.6 mM), implying NPs aggregation was enhanced following the order of ESHA > PPHA > SRFA > SRHA. To investigate the dominant mechanisms, the aggregation of Fh NPs was comprehensively studied under the effects of NOM types, concentrations (0–15 mg C/L) and electrolyte ions (NaCl/CaCl2 beyond CCC). In NaCl/CaCl2, the low concentration of NOM (<7.5 mg C/L) could accelerate NPs aggregation mainly due to patch-charge attraction. When NOM concentration was high (> 7.5 mg C/L), the inhibition effect on NPs aggregation occurred in NaCl due to steric repulsion, whereas the enhancement effect in CaCl2 of aggregation was dominated by the bridging effect. The results indicated that the effects of NOM types, concentration and electrolyte ions should be carefully considered for the environmental behavior of NPs.

Removal of per- and polyfluoroalkyl substances by nanofiltration: Effect of molecular structure and coexisting natural organic matter

This study investigates the removal efficiency of anionic, cationic, and zwitterionic per- and polyfluoroalkyl substances (PFAS) by nanofiltration (NF) in the presence of three representative natural organic matter (NOM) types: bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA). In particular, effects of PFAS molecular structure and coexisting NOM on the transmission and adsorption efficiency of PFAS during NF treatment were analyzed. The results indicate that NOM types dominate membrane fouling behavior despite the coexistence of PFAS. SA exhibits the most significant fouling propensity, resulting in maximum water flux decline. NF effectively removed both ether and precursor PFAS. The effects of the three typical NOM on the membrane-passing behavior of PFAS were consistent for all PFAS investigated. Generally, PFAS transmission decreased in the order of SA-fouled > pristine > HA-fouled > BSA-fouled, indicating that the presence of HA and BSA enhanced PFAS removal while SA declined. Furthermore, reduced PFAS transmission was observed with increased perfluorocarbon chain length or molecular weight (MW), regardless of the presence or type of the NOM. The impacts of NOM on PFAS filtration diminished when the PFAS van der Waals radius was > 4.0 Å, MW > 500 Da, polarization > 20 Å, or LogKow > 3. These findings suggest that both steric repulsion and hydrophobic interactions, especially the former, play important roles in PFAS rejection by NF. This study provides insights into the specific applicability and performance of membrane-based processes for eliminating PFAS during drinking and wastewater treatments, and highlighting the importance of coexisting NOM.

Dissolved Organic Matter and Lignin Modulate Aquatic Toxicity and Oxidative Stress Response Activated by Layered Double Hydroxides Nanomaterials.

Advanced nanomaterials can be released into the environment and can coexist with natural organic matter (NOM). However, evidence on the impacts of NOM on the environmental behavior and toxicity of advanced nanomaterials is still scarce. Here, we investigated the behavior and toxic effects of two layered double hydroxides (LDHs) nanomaterials with different metallic constituents (Mg-Al-LDH and Zn-Al-LDH) at relatively low exposure concentrations on a freshwater green alga (Chlorella pyrenoidosa) in the absence and presence of two types of NOM, namely dissolved organic matter (DOM) and dealkaline lignin (DL). The DOM or DL interaction with the LDHs at different mixture levels was shown to be an antagonistic effect on the growth inhibition toxicity to C. pyrenoidosa mainly. The estimation of the index of Integrated Biological Responses version 2 indicated that the joint interaction of the LDHs with DOM or DL occurred in the following order of frequency synergism > antagonism > additivity. Furthermore, the physicochemical characteristics of LDHs were crucial for illuminating the mechanism by which the DOM or DL modified the LDH-induced oxidative stress response. These findings highlighted the important role of NOM in the behavior and effect of LDHs as a representative of a new class of multifunctional nanomaterials in the freshwater environment.

Adsorption of typical natural organic matter on microplastics in aqueous solution: Kinetics, isotherm, influence factors and mechanism.

With rapid urbanization, microplastics and natural organic matters (NOMs) are ubiquitous in aquatic environment, and microplastics could act as carriers for organic matters in the aqueous solution and may pose a potential risk. In this study, the adsorption behaviors and mechanism of typical NOM, humic acid (HA), on polyvinyl chloride (PVC) and polystyrene (PS) microplastics were investigated. Various influence factors such as solution pH, ions species and concentrations, particle size, and coexisting surfactants were studied. The results suggested that HA adsorption onto PVC and PS was low pH-dependent, and ion species and concentrations have a significant impact on the adsorption capacity. In addition, the particle size of PVC and PS microplastics exhibited a significant correlation with HA adsorption, and the adsorption process was influenced by the surfactant species and concentrations. Moreover, the adsorption behaviors of HA in different real water environments were tested, and UV aging exhibited the opposite effects on adsorption capacity of PVC and PS. Furthermore, the adsorption mechanisms of HA onto PVC and PS were explored, indicating halogen bonding, hydrogen bonding, and π-π interaction play important roles in the adsorption process.

Natural organic matter flocculation behavior controls lead phosphate particle aggregation by mono- and divalent cations

Phosphate addition is commonly applied to remediate lead contaminated sites via the formation of lead phosphate particles with low solubility. However, the effects of natural organic matter (NOM) with different properties, as well as the contributions of specific interactions (particle-particle, particle-NOM, and NOM-NOM) in enhanced stabilization or flocculation of the particles, are not currently well understood. This study investigates the influence of two aquatic NOM and two soil or coal humic acid (HA) extracts on the aggregation behavior of lead phosphate particles and explores the controlling mechanisms. All types of NOM induced disaggregation and steric stabilization of the particles in the presence of Na+ (100 mM) or low (1 mM) Ca2+ concentrations, as well as at low NOM concentrations (1 mgC/L). However, for the soil and coal HA, a threshold at NOM concentrations of 10 mgC/L and high (3 mM) Ca2+ concentrations was observed where bridging flocculation (rather than steric stabilization) occurred. In situ attenuated total reflectance – Fourier transform infrared characterization confirmed adsorption of the soil and coal humic acid extracts (10 mgC/L) onto the surface of the lead phosphate particles in 3 mM Ca2+, whereas dynamic and static light scattering demonstrated extensive HA flocculation that dominated the overall scattered light intensities. These results imply that the accelerated aggregation was induced by a combination of HA adsorption and bridging flocculation by Ca2+. Overall, this research demonstrates that the type of NOM is critical to predict the colloidal stability of lead phosphate particles. Aquatic NOM stabilized the particles under all conditions evaluated, but soil or coal HA with higher molecular weight and aromaticity showed highly variable stabilization or flocculation behavior depending on the HA and Ca2+ concentrations available to adsorb to the particles and participate in bridging. These results provide new mechanistic insights on particle stabilization or destabilization by NOM.

Size-based selectivity of magnetic-layered double hydroxide (MLDH) for efficient removal of oxytetracycline in the presence of natural organic matter

While the adsorption process plays an essential role in antibiotics removal from water, one major problem for applying absorbents in actual wastewater is competitive adsorption that is commonly caused by natural organic matter (NOM). Therefore, we aimed to investigate size-based selectivity of magnetic layered double hydroxides (MLDH) as the absorbent in the mixture of oxytetracycline (OTC) and NOM, as MLDH are generally characterized by high specific surface area, limited intercalation, and ion-exchange properties. MLDH were synthesized by the one-step solvothermal method with four different Fe:Mg ratios and then applied in a series of adsorption experiments. In addition, the role of limited interlayer space of MLDH in the adsorption of OTC and NOM was investigated based on molar mass distribution of those organic components. As results, the adsorption behavior of OTC/NOM on MLDH in the binary systems was found to involve chemisorption and multi-layer coverage. Although the competitive adsorption reduced OTC adsorption, Freundlich coefficient of MLDH (KF) for OTC was higher than KF for NOM, indicating that MLDH selectively adsorbed OTC molecules in the presence of NOM. Moreover, the selectivity (α) value of all MLDH, except MLDH with a Fe:Mg ratio of 1:4, indicating substantial selective adsorption. Among the four MLDH, MLDH11 exhibited the highest α, because its smallest interlayer space offers size-based selectivity, which was also supported by the molar mass distribution. The type of NOM did not significantly affect the OTC adsorption efficiency on MLDH. The results confirmed the benefits of limited interlayer space of MLDH, which offers selectivity for adsorption of OMP in water and shows potential applicability for removing other organic micropollutants.

Nitrite Quantification by Second Derivative Chemometric Models Mitigates Natural Organic Matter Interferences under Chloraminated Drinking Water Distribution System Conditions

Nitrite (NO2−) production in chloraminated drinking water distribution systems (CDWDSs) is among the first bulk water indicators of a nitrification event and is typically quantified using ion chromatography (IC) or colorimetric techniques. NO2− can also be quantified using chemometric models (CMs) formulated using molar absorptivity (Ɛ) and/or ultraviolet absorbance (UVA) spectra, but concerns exist regarding their accuracy and generalizability because of varying source water natural organic matter (NOM), monochloramine (NH2Cl), bromide (Br−), and other species in CDWDSs. We demonstrate that the impact of NOM was mitigated in the second derivative molar absorptivity (Ɛ″) and UVA spectra (UVA″) between 200–300 nm and developed a generalizable CM for NO2− quantification. The Ɛ″+UVA″ CM was calibrated with daily NO2− measurements by IC from five biofilm annular reactor (BAR) tests with feedwater from Fayetteville, Arkansas, USA (FAY1, n = 275) and validated with eight BAR tests (n = 376) with another Fayetteville water (FAY2) and two waters from Dallas, Texas, USA (DAL1 and DAL2). The Ɛ″+UVA″ CM used Ɛ″ for NO2−, nitrate (NO3−), Br−, and NH2Cl at wavelengths of 213-, 225-, 229- and 253 nm, had an adjusted R2 of 0.992 for FAY1 and 0.987 for the other waters, and had a method detection limit (MDL) of 0.050 mg·L−1-N. NO2− challenge samples with three reconstituted NOM types and Br− indicated the Ɛ″+UVA″ CM was generalizable at NOM concentrations like those in the BAR tests (≤ 2.5 mg·L−1-C). The Ɛ″+UVA″ CM accurately simulated NO2− in field tests from two CDWDSs undergoing nitrification, including one with NOM at 3.5 mg·L−1-C, illustrating a practical application of the CM for identifying biological ammonia oxidation.

Mechanistic study of electrooxidation of coexisting chloramphenicol and natural organic matter: Performance, DFT calculation and removal route

The electrooxidation performance of coexisting chloramphenicol (CAP) and natural organic matter (NOM) by Ti4O7 anode was systematically investigated in this study. Intrinsic reaction kinetics showed that the removal of CAP followed pseudo-first-order kinetics, 72.42 ± 0.20 % removal with 40.79 ± 0.41 % mineralization rate of CAP was achieved in 60 min using 5 mA cm−2. The oxidation mechanisms of CAP were elucidated by density functional theory (DFT) simulations and experiments involving hydroxyl free radical (•OH) scavenger, which indicated that the efficient degradation of CAP was attributed to the combined action of •OH attack and direct electron transfer (DET) reaction. The degradation pathway of CAP was proposed based on frontier electron densities (FEDs) calculation and intermediate products identification, and less ecological risks of CAP degradation solution were also proved by acute toxicity test. Humic acid (HA), selected as the typical NOM, could inhibit the degradation of CAP to a certain extent by competitive action for electrooxidation with effective removal and mineralization of HA, which was further confirmed based on real wastewater treatment experiments. Specifically, the degree of humification and aromaticity of HA was weakened, and some complex small molecular organic matters such as aromatic proteins were generated. These findings proved the feasibility of Ti4O7 anode electrooxidation to remove CAP antibiotics and organic matter from water, in consideration of the potential negative role of CAP and organic matter for ecological environment and human health.

Fractionation of levofloxacin and ofloxacin during their transport in NOM-goethite: Batch and column studies

Adsorption and transport of levofloxacin (LEV) and ofloxacin (OFL) enantiomers in a matrix containing goethite and natural organic matter (NOM) were investigated using batch and column experiments. In batch studies, competition and enantioselectivity were observed in the adsorption of LEV and OFL. Enantioselectivity upon adsorption was investigated by comparing changes in the enantiomer fraction (EF) (the ratio of LEV to the sum of LEV and OFL remaining in the solution) after and before adsorption. At pH < 7, there was hardly any selectivity in adsorption of OFL and LEV to goethite. At pH > 7, OFL showed a stronger adsorption than LEV to goethite, and this preference remained when NOM samples of Leonardite humic acid (LHA) and Elliott Soil fulvic acid (ESFA) were added. However, when Suwannee River NOM (SRNOM) was added, the preference was reversed, and LEV was adsorbed more strongly. In single systems, the presence of different types of NOM increased adsorption of LEV and OFL, especially LEV. In column studies, preloaded NOM decreased the transport of LEV and OFL through goethite-coated sand. The EF values in the effluent increased with retention time and reached the largest values (0.59–0.72) at around 1.5 pore volume (PV), and then decreased again, reaching a stable value at 5.0–30.0 PV. Both batch and column experiments showed that, fractionation of LEV and OFL occurred during adsorption and transport in the presence of NOM-goethite complexes, which would eventually affect their environmental fate.

Preferential sorption of polysaccharides on mackinawite: A chemometrics approach

Marine sediments represent the most important sink for natural organic matter (NOM) across geological time spans. Strong associations between minerals, including iron oxides, and organic matter reaching the seafloor play a fundamental role in this preservation and have been known for some decades. Despite the importance of this protective mechanism in the balances of the global carbon budget, very little is known about the affinity of NOM for reduced iron species such as mackinawite (FeS) in the anoxic layers of sediment. In this study, equilibrium partition coefficients (Kd) for three types of NOM (soil extract, corn leaf extract and plankton extract) on FeS were determined through batch sorption experiments. Models were then built via multiple linear regression (MLR) and partial least squares regression (PLSR) in order to predict sorption Kd’s based on the chemical characteristics of the NOM. Investigation of the PLSR regression coefficients indicates that functional groups characteristic of polysaccharides are the greatest positive predictors of NOM sorption onto FeS at marine sediment porewater pH. This conclusion was independently verified by analyses of NOM FTIR spectra pre- and post-sorption. PLSR outperformed MLR with a lower root mean square error of prediction (RMSEP) of 53.4 L/kg compared to 64.0 L/kg. To our knowledge, this research presents a novel machine-learning approach to the quantitative modelling of NOM sorption to minerals found in anoxic marine environments.

Chromium Removal in the Presence of NOM during Fe(II) Reductive Precipitation for Drinking Water Treatment

Cr(VI) is toxic and carcinogenic, which fuels discussions on reducing existing standards for maximum Cr concentrations in drinking water. Fe(II) reductive precipitation is a common and economical method for achieving very low Cr(tot) concentrations (&lt;5 µg/L). While Cr(VI) is reduced to Cr(III), Fe(II) is oxidized to Fe(III). The resulting Cr(III) and Fe(III) have low solubilities at neutral pH, precipitate as hydroxides, and can be removed by conventional media filtration. The presence of natural organic matter (NOM) in the raw water source can, depending on pH, concentration, type of NOM, and contact time, affect this process in various ways, from promoting Cr(VI) reduction, to re-reducing Fe(III), to forming stable complexes with Cr and Fe, thus, impairing chromium removal. The presented data showed that NOM, whether dominated by terrestrial humic acid, or of aquatic origin, could substantially impair chromium removal at neutral pH conditions. In particular, the ultimate removal of Cr(III) was affected. Soluble complexes and/or colloids of Cr(III), Fe(III) and NOM in the size range of 10 kDa–0.1 µm were formed, that could not be removed by conventional media filtration. Presence of iron sludge (&gt;50 mg/L Fe(III)) mitigated the negative impacts of NOM on Cr(VI) reduction and Cr(III) removal. However, even 100 mg/L Fe(III), the highest applied sludge concentration, did not lead to a decrease in Fe(II) dosing requirements under the given conditions. A molar ratio higher than the given stochiometric ratio of [Fe(II)]:[Cr(VI)] = 3 was necessary for sufficient Cr(VI) removal.

Biochar Effectively Inhibits the Horizontal Transfer of Antibiotic Resistance Genes via Restraining the Energy Supply for Conjugative Plasmid Transfer.

Horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs) through plasmid-mediated conjugation poses a major threat to global public health. Biochar, a widely used environmental remediation material, has remarkable impacts on the fate of ARGs. However, although biochar was reported being able to inhibit the HGT of ARGs via conjugation and transformation, little is known about the intracellular process that mediates the inhibition effects. On the other hand, as typical natural organic matter, fulvic acid is a common environmental influencer, and how it interferes with the effect of biochar on the HGT of ARGs is unknown. Therefore, this study investigated the effects on the conjugative transfer of ARGs between Escherichia coli MG1655 and E. coli HB101 carrying plasmid RP4, with biochars pyrolyzed at three temperatures and with the corresponding biochars coating with fulvic acid. Results showed that biochar with higher pyrolyzed temperature had a more substantial inhibitory effect on the conjugative transfer of the RP4 plasmid. The inhibitory effect of biochar was mainly attributed to (i) down-regulation of plasmid transfer gene expression, including the formation of conjugative transfer channel and plasmid replication, due to restrained adenosine triphosphate (ATP) energy supply and (ii) decreased cell membrane permeability. Conversely, the fulvic acid coating diminished this inhibition effect of biochar, mainly by providing more ATP and strengthening intracellular reactive oxygen species (ROS) defense. Our findings shed light on the intracellular process that mediates the effects of biochar on the conjugative transfer of ARGs, which would provide support for using biochar to reduce the spread of ARGs.