Natural Organic Matter Constituents Research Articles

Analysis of natural organic matter chemistry in bentonite clay under compaction using different dry densities and duration

The Nuclear Waste Management Organization of Canada has adopted an adaptive phased management plan for the long-term storage of used nuclear fuel in a Deep Geological Repository (DGR). The DGR barrier system employs copper-coated used fuel containers (UFCs) surrounded by buffer material which is composed of highly compacted bentonite clay. The natural organic matter (NOM) composition of the compacted bentonite is of practical importance for the safety assessment as it regulates the biogeochemical processes at the interface between the UFCs and the buffer layer. However, insufficient investigations on NOM constituents limits the understanding of biogeochemical dynamics in bentonites compacted under different dry densities. This study analyzed the carbon content and NOM composition using targeted compound analysis and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy with bentonites compacted at 1.1, 1.4 or 1.6 g/cm3 dry density for 1, 3, 6, 12 or 18 months. Organic carbon contents were similar across bentonites with different compaction densities at various durations as compared to the reference clay (powdered bentonite sample before compaction). The overall NOM composition measured by solid-state 13C NMR suggested a predominance of alkyl and aromatic carbon in bentonite samples. No marked variations were observed for the NOM components (i.e., alkyl, O-alkyl and aromatic carbon) between the compacted bentonites and the reference clay. Targeted compound analysis revealed that the extractable lipid concentrations in the compacted clays did not significantly vary from the reference bentonite with only some compounds exhibiting nano-gram level differences. Bentonites with relatively lower dry densities (1.1 and 1.4 g/cm3) demonstrated slightly higher extractable compound concentrations, but these differences were not statistically significant. In contrast, the compound concentrations of bentonites compacted to 1.6 g/cm3 were similar or slightly lower compared with the reference bentonite, likely associated with limited microbial growth under high dry compaction density. Taken together, these results suggested that NOM composition and quantity did not significantly alter in bentonites under various pressures nor with longer experimental durations. These findings highlight that compacted bentonite exhibited geochemical stability under the simulated repository environments, which provides critical insight for design and performance of engineered barrier system in a DGR concept.

Fate of sulfamerazine by synchronous adsorption and photocatalysis dependent on natural organic matter properties

ABSTRACT Natural organic matter (NOM) can impede the removal of organic micro-pollutants (OMPs) through several mechanisms, including inner filter effect, competition with the target OMP, and radical scavenging, during synchronous adsorption/photocatalysis of multi-functional composites. In this study, the fate and inhibitory mechanisms of sulfamerazine (SMZ, a model OMP) that occurred in presence of seven different NOM samples (i.e. three standard NOM surrogates, a river water sample, a carbon filter effluent and two different sand filter effluents) during the adsorption/photocatalysis by a composite of Bi2O3-TiO2 supported on powdered activated carbon (Bi2O3-TiO2/PAC, abbreviated as BTP) when exposed to visible light irradiation were revealed. The results indicated that adsorption played a greater attribution than photocatalysis on SMZ removal. The primary impediment to the adsorption and photocatalytic degradation of SMZ was attributed to the presence of terrestrial-derived, humic-like NOM fractions with high aromaticity. The adsorption efficacy of SMZ was weakened by the absorption of NOM and its degradation products onto the BTP surface. The inner filter effect, competition between NOM and SMZ, and radical scavenging were responsible for the reduced photocatalysis of SMZ. In the cases of real water matrices, the presence of inorganic anion and co-existed NOM reduced the removal of SMZ. In summary, the findings of this work offer a comprehensive comprehension of the impact of NOM fractions on photocatalysis, emphasizing the necessity to examine the interplay between NOM and background inorganic constituents in the degradation of OMP via adsorption/photocatalysis.

Selective Transformation of Micropollutants in Saline Wastewater by Peracetic Acid: The Overlooked Brominating Agents.

Peracetic acid (PAA) is an emerging alternative disinfectant for saline waters; HOBr or HOCl is known as the sole species contributing to halogenation reactions during PAA oxidation and disinfection. However, new results herein strongly indicated that the brominating agents (e.g., BrCl, Br2, BrOCl, and Br2O) are generated at concentrations typically lower than HOCl and HOBr but played significant roles in micropollutants transformation. The presence of Cl- and Br- at environmentally relevant levels could greatly accelerate the micropollutants (e.g., 17α-ethinylestraiol (EE2)) transformation by PAA. The kinetic model and quantum chemical calculations collectively indicated that the reactivities of bromine species toward EE2 follow the order of BrCl > Br2 > BrOCl > Br2O > HOBr. In saline waters with elevated Cl- and Br- levels, these overlooked brominating agents influence bromination rates of more nucleophilic constituents of natural organic matter and increase the total organic bromine. Overall, this work refines our knowledge regarding the species-specific reactivity of brominating agents and highlights the critical roles of these agents in micropollutant abatement and disinfection byproduct formation during PAA oxidation and disinfection.

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.

Photocatalytic degradation of organic micropollutants: Inhibition mechanisms by different fractions of natural organic matter

Natural organic matter (NOM) can inhibit the photocatalytic degradation of organic micropollutants (OMPs) through inner filter effect, reactive oxygen species (ROS) scavenging, and competitive adsorption. However, previous studies have focused solely on the bulk properties of NOM and our understanding of the inhibition mechanism by NOM fractions during photocatalytic degradation of OMP is still fragmentary. In this study, five well-characterized different NOM samples (i.e., secondary treated wastewater, river water, and three standard NOM surrogates) were used to elucidate the inhibition mechanisms during photocatalytic degradation of carbamazepine (a model OMP) using TiO2 and its composites with carbon nanotubes (CNT-TiO2) under UVC and solar-light irradiation. The results indicated that terrestrially derived NOM with high aromaticity, a low oxygen/carbon atom ratio, and large molecular weight is the major fraction that participates in ROS scavenging, competitive adsorption, and inner filter effect. Furthermore, the modeling analysis suggested that inner filter effect due to NOM and ROS scavenging was the most influential inhibitory mechanism. In the case of secondary treated wastewater, the presence of high concentrations of inorganic species (e.g., PO43−, Cl−, and NO3−) together with NOM significantly reduced the photocatalytic degradation of carbamazepine. Overall, the methods and the results of this study provide a comprehensive understanding of the effects of NOM fractions on photocatalysis and highlight the need to further consider the interplay between NOM and background inorganic constituents in photocatalytic degradation of OMP.

Mechanistic understanding of the adsorption of natural organic matter by heated aluminum oxide particles (HAOPs) via molecular dynamics simulation

Membrane fouling caused by natural organic matter (NOM) in water is a pressing problem. To address this, heated aluminum oxide particles (HAOPs) have been used as dynamic membranes pre-deposited onto the primary membrane to effectively remove NOM and thereby significantly diminish the fouling potential. An in-depth understanding of the mechanisms underlying the superior performance of HAOPs remains amiss, which motivated this study. Molecular dynamics (MD) simulations were conducted to systematically compare the performance of HAOPs, which have been reported to be particularly effective for high molecular weight (HMW) NOM, with the conventional powdered activated carbon (PAC) adsorbent. Six NOM constituents, three of which have HMW and three have low molecular weight (LMW), were studied. Results indicate that the mechanisms underlying the effective removal of HMW NOM by HAOPs include: (1) higher foulant-HAOPs interaction energy; (2) greater hydration of the HMW NOM, which thereby increases the affinity to the more hydrophilic HAOPs; (3) diminished mobility of the foulant once adsorbed, which deters desorption; and (4) higher peak intensities in the radial distribution functions for multiple functional groups on the HMW NOM foulants. These results are expected to be valuable towards the better design of such materials for mitigating membrane fouling.

Effect of humic acid concentration on pharmaceutically active compounds (PhACs) rejection by direct contact membrane distillation (DCMD)

In this study, a direct contact membrane distillation process was used to achieve rejection of 25 pharmaceutically active compounds (PhACs) in water. The influence of natural organic matter (NOM), a common contaminant in waters that are used for water supply, on PhACs removal was investigated. Humic acid was used as an organic model in order to represent major constituents of NOM. Results indicated that flux decline slightly increased from 0 to 8% as HA feed concentration increased from 0 to 80 mg L−1. Flux decline was mainly associated with membrane fouling which added hydraulic resistance to the transfer of liquid water. Pore wetting was observed when HA concentration increased, which indicated changes in the hydrophobic character of the membrane. MD process showed a rejection of ≥ 99% for the 25 assessed PhACs for all HA concentration evaluated even at high permeate recovery rate (60%), whereas, 24 PhACs presented concentrations below limit detection. The retention of PhACs by MD membrane occurs predominantly by membrane rejection which is mainly governed by volatility and, to a lesser extent, by hydrophobia. The adsorption contribution to PhACs retention was low (<8%) and was significantly associated with positively charged compounds. Although the feed side of the membrane became hydrophilic due to the HA deposit, the PhACs retention by DCMD was not affected, which reinforces the robustness of the process and the ability to produce safe water. Thus, in general, DCMD is less influenced by the feed composition than nanofiltration or reverse osmosis, implicating in higher PhACs rejections.

The Structural Arrangement and Relative Abundance of Aliphatic Units May Effect Long-Wave Absorbance of Natural Organic Matter as Revealed by 1H NMR Spectroscopy

The objective of this study was to shed light on structural features which underlay intensity of long wave absorbance of natural organic matter (NOM) using 1H NMR spectroscopy. For this purpose, a set of the NOM samples was assembled from arctic and nonarctic sampling sites (the Kolyma river basin and Moscow region, respectively). It was to ensure a substantial difference in the humification degree of the isolated organic matter-the biogeochemical proxy of the long-wave absorbance of NOM. The assembled NOM set was analyzed using solution-state 1H NMR spectroscopy. The distribution of both backbone and exchangeable protons was determined using acquisition of spectra in three different solvents. The substantially higher contribution of nonfunctionalized aliphatic moieties CHn (e.g., materials derived from linear terpenoids, MDLT) in the arctic NOM samples was revealed as compared to the nonarctic ones. The latter were characterized with the higher content of CHα protons adjacent to electron-withdrawing groups which belong to carboxyl rich alicyclic moieties (CRAMs) or to aromatic constituents of NOM. We have calculated a ratio of CHn to CHα protons as a structural descriptor which showed significant inverse correlation to intensity of long wave absorbance assessed with a use of E4/ E6 ratio and the slope of absorption spectrum. The steric hindrance of aromatic chromophoric groups of the NOM ensemble by bulky nonfunctionalized aliphatic moieties (e.g., MDLT) was set as a hypothesis for explanation of this phenomenon. The bulky aliphatics might increase a distance between the interacting groups resulting in inhibition of electronic (e.g., charge-transfer) interactions in the NOM ensemble. The obtained relationships were further explored using Fourier transform mass spectrometry as complementary technique to 1H NMR spectroscopy. The data obtained on correlation of molecular composition of NOM with 1H NMR data and optical properties were very supportive of our hypothesis that capabilities of NOM ensemble of charge transfer interactions can be dependent on structural arrangement and relative abundance of nonabsorbing aliphatic moieties.

A novel photodegradation approach for the efficient removal of natural organic matter (NOM) from water

The presence of natural organic matter (NOM) in water can negatively affect water quality if NOM is present in excessive amounts during certain stages of water treatment. It is known that NOM constituents serve as precursors for DBPs (disinfection by-products) during the disinfection step of the water treatment process. Removal of natural organic matter (NOM) before disinfection is therefore essential to control DBP formation; however, owing to the heterogeneity and complexity of NOM, most water treatment processes are unable to attain complete removal of NOM from water sources. There is therefore a great need to develop methods that can effectively degrade NOM into smaller and relatively harmless compounds that are easily removed during water treatment processes. In this study, multi-walled carbon nanotubes/nitrogen, palladium co-doped titanium dioxide (MWCNT/N, Pd co-doped TiO2) (0.5–5% MWCNTs) were fabricated for the enhancement of NOM degradation under visible-light illumination. Different MWCNT/N, Pd co-doped TiO2 (also referred to as CT) nanocomposites were synthesised via a modified sol-gel method and characterised using ultraviolet visible (UV-Vis), X-ray diffraction spectroscopy (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) Spectroscopy and energy-dispersive X-ray spectroscopy (EDS) analysis. The UV-Vis results showed that introducing the MWCNTs on the nanocomposites was accompanied by a red shift, with CT (0.5% MWCNTs) occurring at a longer wavelength than the others. The efficiency and effectiveness of the synthesised nanocomposites was quantified through measuring the NOM degradation rate in raw water samples collected from two South African water treatment plants. These two drinking water treatment plants were selected as the raw water treated in these plants contains different NOM fractions: the raw water treated at Midvaal (MV) Water Company contains transphilic NOM fractions, while that treated at Plettenberg Bay (P) Water Treatment Plant contains high amounts of hydrophobic NOM. The changes in the amount of NOM in a sample were monitored by measuring the UV absorbance at 254 nm (UVA254) as there is a strong correlation between absorbance at this wavelength and the aromatic content. The highest photocatalytic activity was observed with CT (0.5% MWCNTs) which attained 69.4% UVA254 reduction for MV and 97.7% UVA254 reduction for P raw waters. Compared to conventional methods applied by the two water treatment plants of interest, NOM removal efficiency (in terms of UVA254 reduction) by CT (0.5% MWCNTs) increased by up to 9.4% and 11.5% for MV and P water treatment plants, respectively. The enhanced photocatalytic activity of this CT nanocomposite (0.5% MWCNTs) is attributable to the large surface area of the synthesised nanocomposites which allows huge amounts of NOM to be adsorbed onto the surface of the TiO2, thereby increasing their photodegradation. It is also due to the synergistic effect of N and Pd which enhanced the photoactivity of the TiO2 in the MWCNT/N, Pd co-doped TiO2 composite. Overall, it is clear that the use of the conventional processes is not effective in removing NOM from water. Findings obtained show that CT (0.5% MWCNTs) nanocomposite is a promising future NOM removal method that could complement the available water treatment processes in enhancing the removal of the aromatic component of NOM in water.

Exploring the complex removal behavior of natural organic matter upon N-doped reduced graphene oxide-activated persulfate via excitation-emission matrix combined with parallel factor analysis and size exclusion chromatography

Metal-free oxidative degradation by persulfate (PS) is an emerging process as green chemistry without any toxic metal leaching to aquatic environments but has never been explored for natural organic matter (NOM) removal to date. In this study, nitrogen-doped reduced graphene oxide (NrGO) was applied as a catalyst first to investigate the degradation behavior of NOM. A parallel system was also examined without PS for non-oxidative interaction. For three tested NOM, the extent of the removal increased with the addition of NrGO, and the removal rates were consistently higher for the systems with versus without PS (by 25–102%). Specific ultraviolet absorbance (SUVA) exhibited declining trends with NrGO for both oxidative and non-oxidative systems. Up to 86.9%, 59.9%, and 60.3% reduction in SUVA values were found for the oxidative removal of Suwannee River natural organic matter, Suwannee River humic acid, and Suwannee River fulvic acid, respectively. The excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) decomposed fluorescent NOM into two fulvic-like (C1 and C2) and two humic-like (C3 and C4) components. Results implied that more hydrophobic and more condensed aromatic NOM constituents might be preferably removed by both oxidation and adsorption with the greater removal tendency shown for the humic versus the fulvic-like components. Size exclusion chromatography (SEC) demonstrated that large size molecules were more effectively removed by the oxidative versus the non-oxidative interactions with NrGO. Comparative results revealed that adsorption likely played a critical role in determining the preferential removal tendency of the metal-free oxidation toward heterogeneous NOM structures.

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

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

Characteristics of NOM Released to Water from Different Forest and Agricultural Soils

The characteristics of natural organic matter (NOM) released to water from a soil environment were investigated based on the release potential and the quality indexes of SUVA, fluorescence EEM and molecular weight distribution using eight forest and agricultural soils collected from a representative river catchment (Kani River catchment in Gifu, Japan). The content of organic matter (OM) and its release potential to water differed obviously with type of soil origin, in the following order: vegetable field (VF) basic condition [3.5-8.0 m -1 /(mg/L)] > acidic condition [2.5-3.0 m -1 /(mg/L)]. Humic acids (P1), fulvic acids (P2) and protein-like substances (P3) were the main components of the NOM released under neutral condition. The proportion of P1 and P2 released from the forest soils was lower than that from the agricultural soils. Marked differences in UV-absorbing constituents of NOM between forest and agricultural soils were found in the peak with a molecular weight of about 9800 g/mol identified as PSS (polystyrene sulfonate).

Microbial Changes in the Fluorescence Character of Natural Organic Matter from a Wastewater Source

Natural Organic Matter (NOM) is a mixture of aromatic and aliphatic organic compounds of natural origin in any type of aquatic system. Human activities impact the constituents of NOM, from its production to its fate, particularly in the treatment of domestic waste waters. In this work, the impact of microorganisms isolated from a Waste Water Treatment Plant (WWTP) was investigated to determine the fate of NOM fractions in raw sewage, using fluorescence spectroscopy. Wastewater samples were taken at three different times from a WWTP, and incubated for 4 days under two treatments: 1) “raw sewage”, and 2) “spiked”, i.e., the same raw sewage, spiked with bacteria previously isolated from the WWTP. The incubated waters were analyzed by fluorescence spectroscopy, digitally resolved into NOM components: humic- and fulvic-like, and two types of protein-like, i.e., tryptophan- and tyrosine-like, using a Parallel Factor Analysis routine (PARAFAC). The results demonstrate that the “spiked” samples showed the largest changes with incubation time. The signals of the tryptophan- and tyrosine-like components decreased, suggesting a net microbial digestion of proteinaceous material. In contrast, the fulvic-like signals, and to some extent, the humic-like signals increased, suggesting the production of the associated molecular materials during the incubation period. This study provides direct evidence of human impact on the make-up of NOM: the cultures of microbes found at a WWTP consume the proteinaceous material, whereas humic-like and fulvic-like materials are produced.

An ultrahigh-resolution mass spectrometry index to estimate natural organic matter lability.

RationaleDetermining the chemical constituents of natural organic matter (NOM) by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICRMS) remains the ultimate measure for probing its source material, evolution, and transport; however, lability and the fate of organic matter (OM) in the environment remain controversial. FTICRMS-derived elemental compositions are presented in this study to validate a new interpretative method to determine the extent of NOM lability from various environments.MethodsFTICRMS data collected over the last decade from the same 9.4 tesla instrument using negative electrospray ionization at the National High Magnetic Field Laboratory in Tallahassee, Florida, was used to validate the application of a NOM lability index. Solid-phase extraction cartridges were used to isolate the NOM prior to FTICRMS; mass spectral peaks were calibrated internally by commonly identified NOM homologous series, and molecular formulae were determined for NOM composition and lability analysis.ResultsA molecular lability boundary (MLB) was developed from the FTICRMS molecular data, visualized from van Krevelen diagrams, dividing the data into more and less labile constituents. NOM constituents above the MLB at H/C ≥1.5 correspond to more labile material, whereas NOM constituents below the MLB, H/C <1.5, exhibit less labile, more recalcitrant character. Of all marine, freshwater, and glacial environments considered for this study, glacial ecosystems were calculated to contain the most labile OM.ConclusionsThe MLB extends our interpretation of FTICRMS NOM molecular data to include a metric of lability, and generally ranked the OM environments from most to least labile as glacial > marine > freshwater. Applying the MLB is useful not only for individual NOM FTICRMS studies, but also provides a lability threshold to compare and contrast molecular data with other FTICRMS instruments that survey NOM from around the world. Copyright © 2015 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.

Fluorescence analysis of NOM degradation by photocatalytic oxidation and its potential to mitigate membrane fouling in drinking water treatment

This study examined the photocatalytic oxidation of natural organic matter (NOM) as a method to mitigate membrane fouling in drinking water treatment. ZnO and TiO2 photocatalysts were tested in concentrations ranging from 0.05gL−1 to 0.5gL−1. Fluorescence peaks were used as the primary method to characterize the degradation of three specific NOM components – fulvic acid-like humic substances, humic acid-like humic substances, and protein-like substances during photocatalytic oxidation. Fluorescence peaks and Liquid Chromatography–Organic Carbon Detection (LC–OCD) analysis indicated that higher NOM degradation was obtained by photocatalytic oxidation with ZnO than with TiO2. Treatment of the feed water by ZnO photocatalytic oxidation was successful in reducing considerably the extent of hydraulically reversible and irreversible membrane fouling during ultrafiltration (UF) compared to feed water treatment with TiO2. Fouling during UF of water subjected to photocatalytic oxidation appeared to be caused by low molecular weight constituents of NOM generated during photocatalytic oxidation.

Comprehensive characterization of natural organic matter by MALDI- and ESI-Fourier transform ion cyclotron resonance mass spectrometry

Natural organic matter (NOM) is a complex and non-uniform mixture of organic compounds which plays an important role in environmental processes. Due to the complexity, it is challenging to obtain fully detailed structural information about NOM. Although Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) has been demonstrated to be a powerful tool for providing molecular information about NOM, multiple ionization methods are needed for comprehensive characterization of NOM at the molecular level considering the ionizing selectivity of different ionization methods. This paper reports the first use of matrix assisted laser desorption/ionization (MALDI) method coupled with FT-ICR-MS for molecular characterization of NOM within a mass range of 200–800Da. The mass spectral data obtained by MALDI were systematically compared with data generated by electrospray ionization (ESI). It showed that complementary molecular information about NOM which could not be detected by ESI, were provided by MALDI. More unsaturated and aromatic constituents of NOM with lower O/C ratio (O/C ratio<0.5) were preferentially ionized in MALDI negative mode, whereas more polar constituents of NOM with higher O/C ratio were preferentially ionized in ESI negative mode. Molecular anions of NOM appearing at even m/z in MALDI negative ion mode were detected. The results show that NOM molecules with aromatic structures, moderate O/C ratio (0.7>O/C ratio>0.25) and lower H/C ratio were liable to form molecular anions at even m/z, whereas those with higher H/C ratio are more likely to form deprotonated ions at odd m/z. It is speculated that almost half of the NOM molecules identified by MALDI may be aromatic or condensed aromatic compounds with special groups which are liable to absorb electron from other molecules to generate free radical anions during MALDI ionization.

Aggregation Kinetics of Manganese Dioxide Colloids in Aqueous Solution: Influence of Humic Substances and Biomacromolecules

In this work, the early stage aggregation kinetics of manganese dioxide (MnO2) colloids in aqueous solution and the effects of constituents of natural organic matter (i.e., Suwannee River fulvic acid (SRFA), Suwannee River humic acid (SRHA), alginate, and bovine serum albumin (BSA)) were investigated by time-resolved dynamic light scattering. MnO2 colloids were significantly aggregated in the presence of monovalent and divalent cations. The critical coagulation concentrations were 28, 0.8, and 0.45 mM for NaNO3, Mg(NO3)2, and Ca(NO3)2, respectively. The Hamaker constant of MnO2 colloids in aqueous solution was 7.84 × 10(-20) J. All the macromolecules tested slowed MnO2 colloidal aggregation rates greatly. The steric repulsive forces, originated from organic layers adsorbed on MnO2 colloidal surfaces, may be mainly responsible for their stabilizing effects. However, the complexes formed by alginate and Ca(2+) (>5 mM) might play a bridging role and thus enhanced MnO2 colloidal aggregation instead. These results may be important for assessing the fate and transport of MnO2 colloids and associated contaminants.

Behavior of two different constituents of natural organic matter in the removal of sodium dodecylbenzenesulfonate by O 3 and O 3-based advanced oxidation processes

The objective of this study was to analyze the role played by two components of natural organic matter (NOM), gallic acid (GAL) and humic acid (HUM), in the removal of the surfactant sodium dodecylbenzenesulfonate (SDBS) from waters by O 3-based oxidation processes, i.e., O 3/H 2O 2, O 3/granular activated carbon (GAC), and O 3/powdered activated carbon (PAC). It was found that the presence of low concentrations of these compounds (1 mg/L) during SDBS ozonation increases both the ozone decomposition rate and the rate of SDBS removal from the medium. Because of the low reactivity of SDBS with ozone, these effects are mainly due to an increase in the transformation rate of ozone into HO • radicals. Results obtained demonstrate that the presence of GAL and HUM during SDBS ozonation increases the concentration of O −• 2 radicals in the medium, confirming that GAL and HUM act as initiating agents of ozone transformation into HO •. It was also found that this effect was smaller with a larger molecular size of the acid. Presence of GAL and HUM during SDBS removal by O 3/H 2O 2, O 3/GAC, and O 3/PAC systems also increases the SDBS degradation rate, confirming the role of these compounds as initiators of ozone transformation into HO • radicals.

Breakthrough of natural organic matter from fixed bed adsorbers: investigations based on size-exclusion HPLC

Fixed bed adsorption experiments were performed using four granular activated carbon (GAC) columns designed by packing two size ranges of pulverized and sieved Filtrasorb 400 (d=0.5-0.59 and 1.0-1.19 mm) to two bed depths (L=10 and 20 cm), respectively. Continuous supplying of river water containing a lower content of natural organic matter (NOM) allowed investigation of the breakthrough of aqueous natural organic matrices assessed with lumped quality indices of total dissolved organic carbon (DOC) and ultraviolet absorbance at 260 nm (UV260). The capability of GAC columns in dealing with sudden rise in the load of influent NOM was also displayed by intermittently adding to the influent river water a peaty field groundwater that contained a higher content of NOM. Besides, assisted by the size-exclusion HPLC (SEHPLC), changes in the apparent molecular weight distribution of NOM along the bed depth of GAC columns were evaluated, and an important finding revealing relatively even adsorption for adsorbable NOM constituents within the entire molecular weight range of 1000-5200 g mol−1 as PSS (polystyrene sulfonates) detected for the river and groundwater NOM was obtained. Furthermore, using a previously proposed hypothetical multi-component approach incorporating the ideal adsorbed solution theory and a plug flow homogeneous surface diffusion model, the observed concentration profiles of the river water NOM were predicted.

Foulants analyses for NF membranes with different feed waters: coagulation/sedimentation and sand filtration treated waters

Two different NF membranes were operated to remove natural organic matter (NOM) originating from Dongbok Lake in Korea. Coagulation/sedimentation and sand filtration treated waters as membrane feed waters were used. The tested NF membranes were autopsied to compare the fouling propensity from different feed waters using pure water and a NaOH solution. Organic/inorganic foulants onto membrane surface were analyzed in terms of molecular weight (MW) distribution, structure, and IR analysis, and fouled membranes were also characterized in terms of pore size distribution, surface charge, and SEM–EDS analysis. Polysaccharides and/or N-acetyl aminosugar groups with MW ranging from 30,000 to 50,000 g/mol were identified using HP-SEC and IR analysis. Inorganic foulants (i.e., Si and Al) were also fouled onto the membrane surface and/or pores, and it is effectively removed by caustic cleaning, not pure water. Caustic cleaning was proven to be effective to remove both fouled NF membranes as a basis of flux recovery, and it could efficiently desorb the hydrophobic NOM constituents or protein-like substances from the relatively hydrophilic and less negatively charged NF membranes.