Natural Organic Matter Molecules Research Articles

Effect of Water Components on Aggregation and Sedimentation of Polystyrene Nanoplastics

The aggregation and sedimentation of micro/nano-plastics significantly affect their migration and distribution in the environment. This study investigated the effects of Na+ and natural organic matter （NOM） on the aggregation and sedimentation of polystyrene nano-plastics （PS-NPs） in the aqueous phase. Six types of water， such as seawater， lake water， and domestic sewage， were used to evaluate the above effects and other potential influencing factors. The results indicated that Na+ could facilitate the sedimentation of PS-NPs when it was less than 80 mmol·L-1， whereas it could promote the aggregation and suspension of PS-NPs when the concentration was greater than 80 mmol·L-1. NOM molecules affected the aggregation and sedimentation of PS-NPs by changing the ζ potential and relative density of particles via forming a multilayer adsorption structure with Na+ on the particle surface. It was observed that NOM greater than 10 mg·L-1 enhanced the dispersion and suspension of PS-NPs， which might have been attributed to the decrease in relative density of the particles as a large amount of NOM was absorbed onto the surface. Compared with synthetic waters， environmental waters enhanced the aggregation of PS-NPs， which may have been related to the amino acid， protein， and other organic macro-molecules in the water.

Interpreting pH-Dependent Differential UV/VIS Absorbance Spectra to Characterize Carboxylic and Phenolic Chromophores in Natural Organic Matter

Natural organic matter (NOM) is critical for the biogeochemical cycles of energy and many elements in terrestrial and aquatic ecosystems, and protonation-active functional groups in NOM molecules, notably carboxylic and phenolic groups often mediate these critical environmental functions. Molecular heterogeneity, polydispersity and dynamic behavior of NOM complicate achieving an unambiguous description of its molecular properties and reactivity. This study demonstrates that differential ultraviolet-visible (UV/VIS) absorbance spectra (DAS) of NOM acquired at varying pH values exhibit several distinct features associated with the deprotonation of NOM molecules, independent of the environmental provenance of NOM (e.g., surface water, seawater, sediment, and wastewater). The protonation-active functionalities that contribute to the Gaussian distribution bands present in the DAS were identified here by comparing characteristic properties of the bands with the stoichiometries of NOM molecules ascertained by Ultrahigh-Resolution Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). The protonation-active individual chromophores universally present in NOM molecules were identified by a genetic molecular network analysis. The observed DAS features were closely modeled via superimposing DAS spectra of 51 individual protonation-active chromophores. Molecular orbital theory was applied to further interpret the deprotonation of these chromophores, their molecular structure, electron distribution, and electron transitions measured using DAS. The high sensitivity and easy implementation of the DAS approach allows using it as a powerful tool to quantify the molecular properties and reactivity of NOM at environmental concentrations.

Overlooked impacts of natural organic matter conversion in a Fe(II)-induced peroxymonosulfate activation system for river water remediation

The peroxymonosulfate (PMS) process may be hindered severely due to natural organic matter (NOM) conversion in the treatment of emerging pollutants from river water, becoming a critical engineering and technical issue. In this study, a Fe(II)-induced river water (RW)/PMS catalytic system was constructed for investigating molecular transformation of NOM and related influence mechanism to sulfamethoxazole (SMX) degradation. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) analysis indicated that NOM molecules containing no more than one heteroatom in river may be attacked by hydroxyl radicals (OH) and then polymerized, converting into molecules with two or three heteroatoms during PMS oxidation. Based on the correlation analysis, CHONP-NOM, CHOSP-NOM and CHONSP-NOM showed a significant inhibition against SMX degradation, while CHONS-NOM exhibited a moderate inhibitory effect. Besides, more condensed aromatic structures, carbohydrates and tannins were generated via reactive species (OH and sulfate radicals (SO4−)) oxidation, radical addition and polymerization reactions. Notably, condensed aromatic structures, carbohydrates and tannins presented weak, modest and strong inhibition to SMX degradation, respectively. Based on the current results, the inhibition of target pollutants degradation would be mitigated via regulation of NOM molecules in a Fe(II)-induced PMS activation system, providing valuable information to reduce NOM impact. In addition, this study paves the way to achieve efficient removal of emerging pollutants from river water.

Advanced oxidation processes and selection of industrial water source: A new sight from natural organic matter

Natural organic matter (NOM) refers to the dissolved organic matter in natural water that can pass through 0.45μm filter membrane. As a pivotal role in the surface water body, it has a significant effect on the efficiency of AOPs. In this study, Excitation emission matrix - parallel factor (EEM-PARAFAC) analysis is used to elucidate the changes of NOM fluorescence peaks after electrochemical oxidation process, two-dimensional correlation spectroscopy (2D-FTIR-COS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) are utilized to clarify the molecular characteristics of NOM in surface water and the effects of electrochemical oxidation on NOM molecules. The results indicate that parts of NOM molecules are mineralized into simple compounds and precursors of refractory organic matters produced by some NOM molecules after AOPs. It is concluded that the precursors of these refractory organic matters may belong to terrestrial humus (C2). Therefore, for the purpose of avoiding more refractory organic pollutants produced by NOM which can reduce the performance of AOPs in the water treatment process, factories should choose water sources with less humus as industrial water supply, or degrade humus by physical or chemical methods before industrial water supply.

Ozonation/adsorption hybrid treatment system for improved removal of natural organic matter and organic micropollutants from water – A mini review and future perspectives

Elevated concentrations of natural organic matter (NOM) and organic micropollutants (OMPs) can contaminate the quality of drinking water, and current water treatment technologies are not always successful in removing all their constituents. Ozonation and adsorption are two advanced processes with different removal mechanisms used to treat NOM and OMPs. Their treatment efficiency depends on the strength and kinetics of adsorption and ozonation (ozone molecule and OH radical (OH•) reaction) of the individual NOM constituents and OMPs. They are individually able to remove many of the NOM fractions and OMPs but not satisfactory in removing the vast array of their components which differ in their physico-chemical characteristics, for example molecular weight, charge, functional groups, aromaticity, and hydrophobicity/hydrophilicity. Significant progress has been made by integrating these processes (ozonation followed by activated carbon (AC) adsorption) but they need further improvement to efficiently target all NOM fractions and the various OMPs. Ozonation transforms the larger NOM molecules into smaller molecular sizes with lower aromaticity and hydrophobicity, subsequently resulting in reduced adsorption. The reduced adsorption of these molecules diminishes their competition against OMP adsorption resulting in increased OMP removal. Adsorption can remove unoxidized pollutants as well as the by-products of ozonation, and some of them are suspected to be human carcinogens. Of the commonly used adsorbents, anion exchange resin and AC, the former has higher affinity towards negatively charged humic fraction and OMPs. Conversely, the latter has higher affinity towards the hydrophobic constituents and smaller sized constituents which diffuse into AC pores and get adsorbed. Biofilm formed by long-term use of AC also contributes to enhanced removal of NOM and OMPs. This paper briefly reviews the currently available literature on removing NOM and OMPs by the ozonation/adsorption integrated process. It also suggests a new method for further increasing the efficiency of this process.

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

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

Transformation of ammonium to nitrophenolic byproducts by sulfate radical oxidation

Sulfate radical (SO4•−) based oxidation shows great promise in wastewater treatment and subsurface remediation. For the first time, we demonstrated that SO4•− could induce the transformation of ammonium (NH4+) to nitrophenolic byproducts. Using high-resolution mass spectrometry in combination with 15N labeling, mono-nitro and di-nitro phenolic byproducts were identified in a sample containing 1 mM NH4+ and 10 mg/L natural organic matter (NOM) following heat activated peroxydisulfate (PDS) oxidation. At PDS dose of 1 mM, the formation of p-nitrophenol and 5-nitrosalicylic acid reached 0.21 and 0.30 μM, respectively, in 12 h and then decreased; the formation of 2,4-dinitrophenol and 3,5-dinitrosalicylic acid increased monotonically, reaching 0.37 and 0.62 μM, respectively, in 24 h. One-electron oxidation of NH4+ to form aminyl radicals (•NH2) was the first step of the transformation. The reaction of •NH2 with oxygen was a key step in propagating radical chain reactions, leading to nitrogen dioxide radicals (NO2•) as a key nitrating agent. The reactive sites susceptible to nitrating in NOM molecules are not limited to phenolic moieties. We found that aromatic carboxylate moieties could be in situ transformed to phenolics by SO4•−, thus contributed to nitrophenolic byproducts formation as well. Considering the ubiquitous presence of NH4+ in the environment, formation of nitrophenolic byproducts will be widespread when SO4•− is applied for onsite remediation, which should be taken into consideration when evaluating the feasibility of this technology.

Sulfate precipitation treatment for NOM-rich ion exchange brines

Ion exchange (IEX) resins can remove natural organic matter (NOM) from drinking water sources. However, the IEX system produces a waste brine rich of sodium, chloride, NOM and sulfate. The treatment of the waste brine aims to recover a clean solution rich of sodium chloride, that can be reused to regenerate IEX resin. Previous research showed that ceramic nanofiltration partially removes NOM from the waste brine, but sulfate removal requires additional treatment. Sulfate removal by chemical precipitation was previously studied either on brines with low NOM concentrations or water with low concentrations of NOM and salts. The current work focussed on sulfate removal from NOM-rich brines by chemical dosing of (1) BaCl2, resulting in precipitation of barite (BaSO4), and (2) CaCl2, Ca(OH)2 and NaAlO2, resulting in precipitation of calcium sulfate and, subsequently, ettringite (Ca6Al2(SO4)3(OH)12). Additionally, the effect of NOM on SO42− removal was studied. Modelling and batch experiments were conducted with IEX and synthetic brines within the typical ion strength range of 0.1 to 1 M. With doses of 2.2 g of BaCl2 per g of initial sulfate, BaSO4 precipitation removed more than 83 percent of sulfate, resulting in final concentrations below 0.4 g/L even in the presence of NOM. However, NOM inhibited the precipitation of calcium sulfate and, subsequently, ettringite. With doses of 1.3 g of CaCl2, 0.5–0.7 g of Ca(OH)2 and 0.4–0.6 g of NaAlO2 per g of initial sulfate, calcium sulfate and ettringite precipitation removed between 8 and 95 percent of sulfate from NOM-rich brines, resulting in final concentrations between 0.8 and 2 g/L. As a reference, NOM-free brines required doses of 1.3 g of CaCl2, 0.2–0.7 g of Ca(OH)2 and 0.1–0.6 g of NaAlO2 per g of initial sulfate for 89 to 99 percent of sulfate removal, resulting in final concentrations of 0.2 g/L. The inhibition might be attributed to covering of crystal sites by NOM molecules, and to NOM coagulation with aluminium.

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.

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.

Change of disinfection byproducts formation potential of natural organic matter after exposure to persulphate and bicarbonate

Activated persulphate (PS) oxidation is a promising in situ remediation technology for groundwater and soils. Application of this technology to contaminated zones may result in a large quantity of PS residue in the subsurface environment due to inefficient activation and repeated injection. In this study, we demonstrated that natural organic matter (NOM) molecules could be reconfigured due to exposure to unactivated PS and bicarbonate, resulting in reduced disinfection byproducts formation potential in post chlorination process. Fourier transformed inferred spectrometry (FTIR), size exclusive chromotraghy (SEC), and mass spectrometry (MS) analysis revealed that hydroxylation and carboxylation of NOM occurred, followed by inter-molecular coupling via ether bonds. The change of both the reactivity toward free chlorine and molecular structure of NOM during PS/bicarbonate treatment was well mimicked by 3,5-dihydroxylbenzoic acid, suggesting that phenolic moieties in NOM molecules were the main sites underwent transformation in the PS/bicarbonate system. We propose that peroxymonocarbonate (HCO4−) formed upon the reaction between PS and bicarbonate was the main reactive species responsible for the reconfiguration of NOM. It selectively attacked the phenolic moieties via single-electron abstracting mechanism, leading to phenoxy radical intermediates which couple to each other via C–O–C bonds. The findings of this study shed light on the environmental behaviors and impacts of PS in groundwater environment.

Nonhalogenated Aromatic DBPs in Drinking Water Chlorination: A Gap between NOM and Halogenated Aromatic DBPs.

Halogenated disinfection byproducts (DBPs) are generated via reactions with natural organic matter (NOM) in chlorine disinfection of drinking water. How large NOM molecules are converted to halogenated aliphatic DBPs during chlorination remains a fascinating yet largely unresolved issue. Recently, many relatively toxic halogenated aromatic DBPs have been identified in chlorinated drinking waters, and they behave as intermediate DBPs to decompose to halogenated aliphatic DBPs. There is still one gap between NOM and halogenated aromatic DBPs. In this study, nine nonhalogenated aromatic compounds were identified as new intermediate DBPs in chlorination, including 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 3-formyl-4-hydroxybenzoic acid, salicylic acid, 5-formyl-2-hydroxybenzoic acid, 4-hydroxyphthalic acid, 4'-hydroxyacetophenone, 4-methylbenzoic acid, and 4-hydroxy-3-methylbenzaldehyde. These nonhalogenated aromatic DBPs formed quickly and reached the maximum levels at relatively low chlorine doses within a short contact time, and their formation pathways were proposed. The formation kinetics of three nonhalogenated aromatic DBPs and their corresponding monochloro-/dichloro-substitutes during chlorination were then modeled. The nonhalogenated aromatic DBPs contributed up to 84% of the formed monochloro-substitutes and 22% of the formed dichloro-substitutes, demonstrating that they somewhat acted as intermediates between NOM and halogenated aromatic DBPs. Furthermore, the formed nonhalogenated aromatic DBPs were found to be removed by >50% by granular activated carbon adsorption.

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.

Interactions between natural organic matter (NOM) and the cationic dye toluidine blue at varying pHs and ionic strengths: Effects of NOM charges and Donnan gel potentials

This study examined effects of charges of molecules of natural organic matter (NOM) on its interactions with organic cations represented by toluidine blue (TB). NOM was exemplified in this study by Suwannee River (SR) and South Platte (SP) NOM. TB/NOM interactions were probed in the range of pH 3 to 11, DOC concentrations 0–10.6 mg L−1 and ionic strengths 0.001–0.1 mol L−1. Changes of TB absorbance at indicative wavelengths of 640 and 550 nm located in the characteristic absorbance band of TB and their ratio R640/550 were used to quantify TB/NOM binding and the formation of TB dimers and possibly higher order aggregates in the Donnan volume of NOM molecules. These effects were interpreted based on the modeling of NOM charges and their Donnan gel potentials (ψD). The spectroscopic and modeling data showed that TB/NOM binding can be quantified via a complexation model that reflects the extent of electrostatic attraction between TB cations and anionic NOM molecules. The dependence of the apparent formation constant vs. ionic strength was shown to be qualitatively correlated with the ψD potentials of NOM molecules.

The Removal of CuO Nanoparticles from Water by Conventional Treatment C/F/S: The Effect of pH and Natural Organic Matter.

The increased use of engineered nanoparticles (ENPs), such as copper oxide nanoparticles (CuO NPs), in commercial products and applications raises concern regarding their possible release into freshwater sources. Therefore, their removal from water is important to eliminate adverse environmental and human health effects. In this study, the effects of pH and natural organic matter (NOM), i.e., humic acid (HA) and salicylic acid (SA) on the removal of CuO NPs by coagulation/flocculation/sedimentation (C/F/S) were evaluated. The results indicated that pH significantly affects the coagulation efficiency, where 10–60% CuO NPs removal was achieved under extreme acidic/alkaline conditions. However, at neutral pH, removal of up to 90% was observed with a lower ferric chloride (FC) dosage (0.2 mM). The coagulation efficiency and mechanism were strongly affected by the type of Fe species present in the aqueous phase, which is mainly controlled by pH. Higher concentrations of both HA and SA decrease the CuO NPs agglomeration rate, and thereby improve the colloidal stability due to the NOM molecules adsorbed onto the NPs surface. The presence of hydrophobic HA needs a higher FC dosage of 0.5–0.8 mM than a dosage of hydrophilic SA of 0.25–0.35 mM, to obtain a similar CuO coagulation efficiency. Moreover, higher removals of dissolved organic carbon (DOC) and UV254 were observed more in hydrophobic NOM than in hydrophilic. The results of the Fourier transform infrared (FT-IR) analysis of FC composite flocs confirm that the charge neutralization and enmeshment of coagulant might be a possible removal mechanism. The findings of the current study may provide critical information in the prediction of the fate, mobility, and removal of CuO NPs during C/F/S in water treatment.

Ferrate(VI) decomposition in water in the absence and presence of natural organic matter (NOM)

The kinetics of ferrate(VI) decomposition in natural water were assessed in the absence and presence of natural organic matter (NOM) (pH = 7.50, [Fe(VI)] = 54 µM, DOC = 0.00–10.00 and 1.00–8.57 mg/L for a simulated natural water and six real natural waters, respectively). Without NOM, Fe(VI) decomposition in simulated natural water exhibited a biphasic kinetics pattern, i.e. a 2nd-order reaction with respect to Fe(VI) concentration followed by a 1st-order reaction. However, an additional instant Fe(VI) loss was observed at the onset in the presence of NOM for both simulated and real natural waters, thereby rendering Fe(VI) decay with NOM a unique three-stage kinetics pattern. The initial instant Fe(VI) loss was caused due to the homogenous Fe(VI) self-decay and the rapid reactions between Fe(VI) and NOM. The latter accounted for a major fraction of the initial Fe(VI) loss and was in direct proportion with the initial DOC (DOC0) (Δ[Fe(VI)]0DOC = αNOM DOC0; αNOM = 1.45 µM Fe(VI)·L/mg DOC for the simulated natural water, and 0.66–1.35 µM Fe(VI)·L/mg DOC for the six natural waters). Fe(VI) decomposition experiments with different Suwannee River NOM isolates revealed that hydrophobic NOM fractions (i.e. fulvic acid (FA) and humic acid (HA)) caused a more significant initial Fe(VI) loss than the hydrophilic group (HPI), suggesting that Fe(VI) preferentially reacted with hydrophobic NOM molecules rather than hydrophilic compounds. Furthermore, an approach developed for the estimation of αNOM revealed a linear correlation between αNOM and specific UV absorbance (SUVA) (αNOM = 0.27SUVA + 0.18, R2 = 0.71). This study provides essential information regarding Fe(VI) decomposition for the determination of Fe(VI) dose and exposure for effective water treatment.

Natural Organic Matter Concentration Impacts the Interaction of Functionalized Diamond Nanoparticles with Model and Actual Bacterial Membranes.

Changes to nanoparticle surface charge, colloidal stability, and hydrodynamic properties induced by interaction with natural organic matter (NOM) warrant consideration in assessing the potential for these materials to adversely impact organisms in the environment. Here, we show that acquisition of a coating, or "corona", of NOM alters the hydrodynamic and electrokinetic properties of diamond nanoparticles (DNPs) functionalized with the polycation poly(allylamine HCl) in a manner that depends on the NOM-to-DNP concentration ratio. The NOM-induced changes to DNP properties alter subsequent interactions with model biological membranes and the Gram-negative bacterium Shewanella oneidensis MR-1. Suwannee River NOM induces changes to DNP hydrodynamic diameter and apparent ζ-potential in a concentration-dependent manner. At low NOM-to-DNP ratios, DNPs aggregate to a limited extent but retain a positive ζ-potential apparently due to nonuniform adsorption of NOM molecules leading to attractive electrostatic interactions between oppositely charged regions on adjacent DNP surfaces. Diamond nanoparticles at low NOM-to-DNP ratios attach to model membranes to a larger extent than in the absence of NOM (including those incorporating lipopolysaccharide, a major bacterial outer membrane component) and induce a comparable degree of membrane damage and toxicity to S. oneidensis. At higher NOM-to-DNP ratios, DNP charge is reversed, and DNP aggregates remain stable in suspension. This charge reversal eliminates DNP attachment to model membranes containing the highest LPS contents studied due to electrostatic repulsion and abolishes membrane damage to S. oneidensis. Our results demonstrate that the effects of NOM coronas on nanoparticle properties and interactions with biological surfaces can depend on the relative amounts of NOM and nanoparticles.

New Insights into Trihalomethane and Haloacetic Acid Formation Potentials: Correlation with the Molecular Composition of Natural Organic Matter in Source Water.

Natural organic matter (NOM) represents the major source of precursors for disinfection byproducts (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAAs), formed during disinfection of drinking water, but the molecular composition and reactivity of NOM remain not well understood. In this study, electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to characterize the molecular composition of NOM of 20 source waters taken across China for the purpose of determining the major precursors of THMs and HAAs at molecular level. It was found that there is a core of NOM compositions that are ubiquitous in different source waters, which is supposed to be more relevant for NOM quality. Formation potentials (FP) of THMs and HAAs were determined for NOM from different source waters during chlorination. Spearman's rank correlation was used to link THMFP and HAAFP with the individual molecular composition of NOM. Significant correlation (P < 0.001) was found between DBPFP and the NOM molecules with a high O/C ratio and low H/C ratio, indicating these molecules could contribute greatly to the formation of THMs and HAAs during chlorination. The link of THMFP and HAAFP with individual NOM molecules may allow us to develop more effective treatment strategies to achieve the drinking water safety objective: effective disinfection of waterborne pathogens while minimizing toxic DBPs.

Ion Accumulation Time Dependent Molecular Characterization of Natural Organic Matter Using Electrospray Ionization-Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Natural organic matter (NOM) is a complex organic mixture and plays a crucial role in environmental processes. By using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), detailed molecular information on NOM could be achieved. In this paper, ion accumulation time (IAT), a key parameter of FTICR-MS for complex mixture detection, was the focus, and its effect on the molecular characterization of NOM by FTICR-MS was systematically investigated. A notable feature of selective detection of NOM molecules by FTICR-MS with different IAT was observed. Most of the polar molecules with high O/C ratio (O/C ratio >0.5) could be easily detected by FTICR-MS with a short IAT, but extending IAT led to the ion intensities of these molecules decreasing or even disappearing. Meanwhile, a large number of unsaturated and aromatic molecules with low O/C ratio (O/C ratio <0.6) and low polarity, all of which could not be observed with a short IAT, were remarkably detected by extending IAT. Results also revealed that the unsaturated and aromatic molecules, which could only be observed by extending the IAT, were not generated by the fragmentation of molecules in NOM or from the dissociation of NOM aggregations but originally existed in NOM samples. The selective detection of NOM molecules caused by IAT extension was possibly attributed to their different polarity and different stability in the collision cell. On the basis of these results, a novel strategy of combining mass spectrometric data of NOM obtained with different IAT by FTICR-MS was proposed. With this strategy, more than 4715 CHO-molecular formulas were assigned, where about 2000 more formulas were obtained in comparison with using a short IAT (2733 CHO-molecular formulas identified) solely. The strategy is simple and robust and can be used as an alternative method to obtain more molecular information on NOM in the environment.

Effect of water chemistry and operational conditions on μGAF process performance

Microgranular adsorptive filtration (μGAF) is a water treatment technique in which adsorption and granular media filtration operate simultaneously as water passes through a thin layer of adsorbent pre-deposited on a woven mesh or membrane. Our previous work showed that when heated aluminum oxide particles (HAOPs) are the adsorbent in such systems, substantial natural organic matter (NOM) removal and fouling reduction can be achieved. The present study investigated the effects of feed water chemistry and operational conditions on μGAF performance. Parameters investigated include the pH, ionic strength, and concentration of divalent cations in the feed, the flux through the adsorbent layer, and the pressure drop across both the adsorbent layer and the membrane. In the range from pH 3 to 9, lower pH promoted removal of NOM in general, and transparent exopolymer particles (TEP) in particular, by HAOPs. These enhanced removals led to increased fouling of the HAOPs layer and reduced fouling of a downstream membrane. Higher ionic strength exacerbated fouling of the bare membrane but had little effect on the ability of HAOPs to collect foulants from the feed. Increased concentrations of divalent cations reduced membrane fouling slightly, possibly due to the agglomeration of polysaccharides caused by divalent cations. Increasing the flux through the HAOPs layer had essentially the same effect as lowering the pH of the feed – it enhanced removal of NOM and TEP by, and increased fouling of, the HAOPs layer, thereby reducing fouling of the downstream membrane.The HAOPs layer was incompressible, even when some NOM had accumulated on or in it, suggesting that NOM molecules adsorb on the HAOPs throughout the layer and do not form a continuous gel layer on top of the HAOPs layer. Particulate and colloidal matter were inferred to be the dominant foulants in μGAF units, whereas soluble NOM (including soluble TEP) was the key foulant in the downstream membrane units.