Immobilization of fission iodine by reaction with insoluble natural organic matter

Iodine-129 is a fission product and highly mobile in the environment. Along with other stable isotopes of iodine, ¹²⁹I is released during reprocessing of nuclear fuel and must be trapped to prevent the release of radioactivity to the environment. Past studies have provided evidence that iodine can become associated with natural organic matter (NOM). This research explores the use of NOM (sphagnum peat and humic acid) to sequester iodine from the vapor and aqueous phases. NOM-associated iodine may be stable for geological storage. NOM-sequestered iodine can be recovered by pyrolysis to prepare target materials for transmutation. The nature of the NOM-iodine association has been explored.     

Capillary zone electrophoresis of natural organic matter

This paper presents an in-depth look at the use of capillary electrophoretic (CE) techniques for the fingerprinting and characterization of humic substances and natural organic matter. These materials are highly heterogeneous in structure and show all characteristics of mixtures unliked in analytical chemistry. The electrophoretic approach, however, allows the determination of mobility distributions in different solution conditions, representative of the effective charge and size distribution status of the components present. A tabulated review covers over 50 references on the subject and highlights the possibilities and problems encountered in the analysis of such polydisperse materials with CE methods. In a second part of the article the consequences of experimental and buffer parameters on the behavior of humic materials in CE are presented.     

Membrane distillation of NaCl solution containing natural organic matter

The concentration of NaCl solution containing natural organic matter by membrane distillation (MD) has been performed. The salt solution produced during animal intestines processing was used as a feed. The presence of organic compounds in the feed caused the fouling of MD membranes. The experiments were performed with polypropylene capillary membranes. A rapid flux decline caused by the deposition of organic matter on the membrane surface has been observed. The morphology and composition of the fouling layer was studied using scanning electron microscopy (SEM) coupled with energy dispersion spectrometry (EDS) and Fourier transform infrared with diffuse reflectance spectroscopy (FTIR-DRS). Protein and sodium chloride constituted the major components of the gel layer. Rinsing of the MD module with a 2 wt.% citric acid solution removed a part of the fouling layer. Boiling of spent NaCl solution followed by filtration resulted in the separation of the organic matter in the form of a deposit. This enabled a significant reduction in the occurrence of fouling phenomenon.     

Kinetic determination of some inorganic and organic compounds by oxidation with iodate

Sulphite (5.0 × 10^?1?5.0 × 10^?3 M), ascorbic acid and other compounds are oxidized by potassium iodate in dilute sulphuric acid; the production of iodide is monitored by an iodide-selective electrode. The time needed for a 40-mV potential change is inversely proportional to concentration. For sulphite (1.0 × 10^?5?1.0 × 10^?4 M), selectivity is improved by sweeping the sulphur dioxide formed in acidic EDTA-containing solution into the iodate solution.     

Effects of adsorbents on membrane fouling by natural organic matter

Fouling by natural organic matter (NOM) is a major impediment to cost-effective operation of membrane processes in water treatment. This research investigated the removal of NOM by three adsorbents: heated iron or aluminum oxide particles (HIOPs and HAOPs, respectively) and powdered activated carbon (PAC). Although PAC removed a larger fraction of the DOC than did either HAOPs or HIOPs, it adsorbed non-fouling molecules preferentially over foulants, whereas the opposite was true for the metal oxide particles. In addition, when the oxide adsorbents were pre-deposited on a microfiltration membrane, foulants that were not adsorbed in batch tests were effectively removed from the solution before it reached the membrane, leading to excellent performance with respect to both NOM removal and fouling. SEM images showed that membranes under a layer of HAOPs and HIOPs were virtually as clean as a pristine membrane.     

Influence of inorganic scalants and natural organic matter on nanofiltration membrane fouling

The influence of inorganic scalants and NOM on nanofiltration (NF) membrane fouling was investigated by a crossflow bench-scale test cell. Mathematical fouling models were used to determine kinetics and fouling mechanisms of NF membrane. It was observed that, with natural organic matter (NOM) at a concentration of 10 mg L⁻¹, divalent cation, i.e. calcium (Ca²⁺), exhibited greater flux decline than monovalent cation, i.e. sodium (Na⁺), while solution flux curves dominated cake formation model, especially at high ionic strength. For inorganic scalants of polyanions, i.e. carbonate (CO₃²⁻), sulphate (SO₄²⁻), and phosphate (PO₄³⁻), solution flux curves were relatively fitted well with pore blocking model, possibly due to precipitated species formed and blocked on membrane surface and/or pores. For different divalent cations (i.e. calcium and magnesium (Mg²⁺)), calcium showed greater flux decline than magnesium, possibly due to higher concentration of precipitated calcium species than that of precipitated magnesium species based on the pC (−log concentration) and pH diagram.     

Transmission electron microscopy of the natural organic matter of surface waters

Some components of aquatic natural organic matter (NOM) can be analysed effectively by methods of particle analysis employing transmission electron microscopy in conjunction with multi-method analytical approaches in the field, minimum perturbation techniques for sample handling and technology transfer from the biomedical sciences. The NOM components, include fulvic acids, colloidal fibrils and organic polymers of MW > 30 000. The use of a water-compatible embedding resin permits shape and size analyses of colloidal NOM (1–1000 nm) in ultrathin sections which minimize the misleading dehydration artifacts of the past. Experimentally induced perturbations allow one to follow aggregation/coagulation events at 1 nm resolution, while permitting the analyst to relate some components of coagulum structure to chemical entities. This review presents the current status of attempts to optimize a combination of analytical chemistry and transmission electron microscopy for describing NOM and its behaviour in surface waters.     

Kinetics of Cu(II) reduction by natural organic matter

The kinetics of Cu(II) reduction by Suwannee River fulvic acid (SRFA) at concentrations from 0.25 to 8 mg L(-1) have been investigated in 2 mM NaHCO(3) and 0.7 M NaCl at pH 8.0. In the absence of oxygen, SRFA reduced Cu(II) to Cu(I) in a biphasic manner, with initial rapid formation of Cu(I) followed by a much slower increase in Cu(I) concentration over time. When present, oxygen only had a noticeable effect on Cu(I) concentrations in the second phase of the reduction process and at high [SRFA]. In both the absence and presence of oxygen, the rate of Cu(I) generation increased with increasing [SRFA]. At 8 mg L(-1) [SRFA], nearly 75% of the 0.4 μM Cu(II) initially present was reduced to Cu(I) after 20 min, although the yield of Cu(I) relative to [SRFA] decreased at [SRFA] > 1 mg L(-1). Two plausible kinetic modeling approaches were found to satisfactorily describe the experimental data over a range of [SRFA]. Despite some uncertainty as to which approach is correct, common features of both approaches were complexation of Cu(II) by SRFA and reduction of Cu(II) by two different electron donor groups within SRFA: a relatively labile electron donor (with a concentration of 1.1 × 10(-4) equiv of e(-) (g of SRFA)(-1)) that reduced Cu(II) relatively rapidly and a less labile donor (with a concentration of 3.1 × 10(-4) equiv of e(-) (g of SRFA)(-1)) that reduced Cu(II) more slowly.     

Preparation of a novel magnetic resin for effective removal of both natural organic matter and organic micropollutants

A novel,bifunctional,hypercrosslinked.magnetic resin W2 was prepared using divinylbenzene(DVB) and glycidyl methacrylate(GMA) as comonomers in three steps(i.e.,suspension polymerization, amination and post-crosslinking reactions).To evaluate the adsorption of natural organic matter(NOM) and organic micropollutants(OMPs) on the obtained resin W2,two magnetic resins Wl(the precursor of W2 before post-crosslinking) and WO(the precursor of Wl before amination) were chosen for comparison.The results indicated that W2 would be a promising material for the removal of both NOM and OMPs from aquatic environments.     

Removal of natural organic matter by ultrafiltration with TiO2-coated membrane under UV irradiation

This study investigates the performance of ultrafiltration (UF) by membranes coated with titanium dioxide (TiO2) photocatalyst under ultraviolet (UV) illumination in removing natural organic matter (NOM) and possibly in reducing membrane fouling. Experiments were carried out using heat-resistant ceramic disc UF membranes and humic acids as model substances representing naturally occurring organic matter. Membrane sizes of 1, 15, and 50 kDa were used to examine the effects of coating under ultraviolet irradiation. A commercial humic solution was subjected to UF fractionation (batch process); gel filtration chromatography was applied to study the effects of molecular weight distribution of NOM on UF membrane fouling. When compared to naked membranes, UV254 (ultraviolet light of lambda=254 nm) illumination of TiO2-coated membranes exhibits more flux decline with similar effluent quality. Although the UF membrane is able to remove a significant amount of humic materials, the incorporated photocatalysis results in poor performance in terms of permeate flux. The TiO2-coated membrane under UV254 irradiation alters the molecular weight (MW) distribution of humic materials, reducing them to <1 kDa, which is smaller than the smallest (1-kDa) membrane in this study. Thus, TiO2-coated membranes under UV254 irradiation do not perform any better in removing natural organic matter and reducing membrane fouling.     

Photodegradation of natural organic matter exposed to fluctuating levels of solar radiation

Irradiation of natural water samples with natural or artificial UVR typically results in a progressive loss of color and decreased absorbance; a process often referred to as photobleaching. In a typical photobleaching experiment, samples are exposed to a relatively constant level of artificial or natural UVR. However, under most natural situations, the vertical mixing of the water within the upper mixed layer results in strong and periodic fluctuations in UV irradiance. In this paper, we present the results of an experiment in which natural lake water was exposed to solar radiation in quartz tubes that were incubated either at fixed depths or rotating within the water column. We found differences between rotating and fixed samples in (i) photobleaching, (ii) nutrient release, and (iii) subsequent use by algae and bacteria. The evidence presented in this study demonstrated that photochemical processes might be affected by vertical water motion. The reasons for such differences remain largely unknown. Although we offer a potential explanation for such differences, our proposed mechanism is based on a post-hoc analysis of the data and should be taken solely as a working hypothesis for future research.     

Adsorption of organic matter at mineral/water interfaces: 5. Effects of adsorbed natural organic matter analogues on mineral dissolution

The effects of the adsorption of pyromellitate, an analogue for natural organic matter, on the dissolution behavior of corundum (alpha-Al2O3) have been examined over a wide range of pyromellitate concentrations (0-2.5 mM) and pH conditions (2-10). The adsorption modes of pyromellitate on corundum have first been examined using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and are shown to be dominated by a fully deprotonated, outer-sphere pyromellitate species ([triple bond]AlOH2+. . .Pyr4-) at pH >/= 5.0. At lower pH conditions, however, an additional protonated outer-sphere species ([triple bond]AlOH2+. . .H2Pyr2-) and an inner-sphere species are also evident. In accordance with the ATR-FTIR findings, modeling of macroscopic pyromellitate adsorption data using an extended constant capacitance treatment was possible using two outer-sphere ([triple bond]AlOH2+. . .Pyr4- and [triple bond]AlOH2+. . .H2Pyr2-) and one inner-sphere ([triple bond]AlPyr3-) adsorbed pyromellitate species. The presence of adsorbed pyromellitate strongly inhibited the dissolution of corundum under acidic (pH < 5) conditions, consistent with a mechanism previously proposed by Johnson et al. whereby outer-spherically adsorbed Pyr4- species sterically protect dissolution-active surface sites from attack by dissolution-promoting species such as protons. A reduction in the protolytic dissolution rate of corundum results. A reference Suwannee River fulvic acid, which also adsorbs to aluminum (oxyhydr)oxide surfaces in a predominantly outer-sphere manner, was similarly shown to strongly inhibit the dissolution of corundum at pH = 3.     

Colloidal behavior of aluminum oxide nanoparticles as affected by pH and natural organic matter

The colloidal behavior of aluminum oxide nanoparticles (NPs) was investigated as a function of pH and in the presence of two structurally different humic acids (HAs), Aldrich HA (AHA) and the seventh HA fraction extracted from Amherst peat soil (HA7). Dynamic light scattering (DLS) and atomic force microscopy (AFM) were employed to determine the colloidal behavior of the NPs. Influence of pH and HAs on the surface charges of the NPs was determined. zeta-Potential data clearly showed that the surface charge of the NPs decreased with increasing pH and reached the point of zero charge (ZPC) at pH 7.9. Surface charge of the NPs also decreased with the addition of HAs. The NPs tend to aggregate as the pH of the suspension approaches ZPC, where van der Waals attraction forces dominate over electrostatic repulsion. However, the NP colloidal suspension was stable in the pHs far from ZPC. Colloidal stability was strongly enhanced in the presence of HAs at the pH of ZPC or above it, but in acidic conditions NPs showed strong aggregation in the presence of HAs. AFM imaging revealed the presence of long-chain fractions in HA7, which entangled with the NPs to form large aggregates. The association of HA with the NP surface can be assumed to follow a two-step process, possibly the polar fractions of the HA7 sorbed on the NP surface followed by entanglement with the long-chain fractions. Thus, our study demonstrated that the hydrophobic nature of the HA molecules strongly influenced the aggregation of colloidal NPs, possibly through their conformational behavior in a particular solution condition. Therefore, various organic matter samples will result in different colloidal behavior of NPs, subsequently their environmental fate and transport.     

Indirect kinetic spectrophotometric determination of hydroxylamine based on its reaction with iodate.

A simple, precise and accurate method is proposed for rapid determination of trace amounts of hydroxylamine based on the reaction of hydroxylamine with iodate in acidic media. The reaction of neutral red by the produced nitrite ion was used to monitor the reaction spectrophotometrically at 525 nm by a fixed time method. Hydroxylamine in the range of 0.0400-1.200 microg mL(-1) could be determined. The relative standard deviation for 10 determinations of 0.500 microg mL(-1) hydroxylamine was 1.81% and the limit of detection was 0.010 microg mL(-1). The proposed method was applied to the determination of hydroxylamine in water samples with satisfactory results.     

Feed-water pretreatment: methods to reduce membrane fouling by natural organic matter

The prevention of fouling of polysulphone ultrafiltration membranes, used for the purification of natural brown water, was investigated by pretreating the feed-water prior to filtration. Natural brown water was pretreated by changing the pH of the feed solution and by coagulation with metal-ions prior to filtration. Specific characterisation techniques, developed by Maartens et al. (1998) [A. Maartens, P. Swart, E.P. Jacobs, Humic membrane foulants in natural brown water: characterization and removal, Desalination 115 (3) (1998) 215–227] and Jucker and Clarke (1994) [C. Jucker, M.M. Clark, Adsorption of aquatic humic substances on hydrophobic ultrafiltration membranes, J. Membrane Sci. 97 (1994) 37–52], were used to determine and compare the effects induced by the adsorption of natural organic matter on the permeability of capillary ultrafiltration membranes. The extent of foulant adsorption and the quality of the resultant permeate solutions were determined by UV–VIS-light spectroscopy. Results indicated that adsorption of natural organic matter can be minimised by adjusting the pH of the feed solution to 7. The findings of this investigation provides information of importance for the operation of future natural brown water ultrafiltration plants.     

The ionic strength effect on microcystin and natural organic matter surrogate adsorption onto PAC

This work aims to contribute to a better understanding of the ionic strength effect on microcystin and natural organic matter (NOM) surrogate adsorption by analyzing the importance of adsorbate molecular size, and surface concentration. Adsorption kinetics and/or isotherms were performed on PAC Norit SA-UF for four microcystin variants (MC-LR, MC-LY, MC-LW, MC-LF), and three NOM surrogates (salicylic acid (SA), tannic acid (TA), Aldrich humic acid (AHA)) at different solution ionic strengths. Results showed that the ionic strength effect depends upon the adsorbate surface concentration, cation charge (mono or divalent), and adsorbate molecular size. Potassium seemed not to affect the MC-LR adsorption, while calcium enhanced MC-LR kinetics and adsorption capacity. K+ and, particularly, Ca2+ improved the adsorption kinetics of the other microcystin variants. For identical surface concentration and ionic strength, the impact of K+ and Ca2+ on NOM surrogates depended on the adsorbate molecular size: K+ effect was only observed for AHA, whereas Ca2+ caused no effect on SA adsorption, slightly enhanced TA adsorption, and greatly enhanced AHA adsorption. MC-LR isotherms with two salt concentrations (KCl or CaCl2) indicated that, for the studied range of equilibrium surface concentration (5.3-18.7 mg/g), an enhanced adsorption regime prevails, and no transition regime was observed.     

Structure and stability of natural organic matter/soil complexes and related synthetic and mixed analogues

This review aimed at the presentation of recent, new approaches which have been developed to improve our knowledge of soil structure and some related characteristics. The investigations reviewed addressed a large number of solid/polymer systems, from strictly synthetic to fully natural systems. Only studies correlating adsorption and solid structuring were considered, so that a great number of adsorption studies were not taken into account.Despite the very complex chemical nature, composition and structure of natural organic matter and soils, some analogues appeared to be useful for determining the role of the natural substances in the stability of soils. Stability means that the soil was able to resist fragmentation and dispersion induced by successive drying and wetting processes. Actually, in the domain of low polymer content, the cohesion of soils was found to be correlated to the concentration of natural organic matter and established by a mechanism which is similar to that inducing the flocculation of suspended colloidal particles. The paper reviews some characteristics of synthetic, natural and mixed systems which display the correlation existing between the structuring of solid agglomerates and the adsorption of polymers.     

Measurement and computation of zinc binding to natural dissolved organic matter in European surface waters

The zinc binding characteristics of natural dissolved organic matter (DOM) from five representative European surface freshwater sources were studied by square wave anodic stripping voltammetry (SWASV) and model simulation. Water samples were titrated with zinc and free zinc ion activity {Zn²⁺}, was calculated from the measurement of labile zinc by SWASV and other system conditions. Measured values of {Zn²⁺}, which were in the range 10⁻⁷ to 10⁻⁵ M, were compared with those simulated using Humic Ion-Binding Models V and VI. It was assumed that zinc speciation was controlled by the organic matter, represented by fulvic acid (FA), together with inorganic solution complexation. The models were calibrated by adjusting the parameter DOMFA, the proportion of DOM considered to behave as FA. Two modeling scenarios were used to obtain DOMFA values, both considering and not considering the competitive effects of Al, Fe(II) and Fe(III). The default Zn-DOM binding strength in Model VI (log K_MA = 1.6) was not able to provide realistic values of DOMFA and a log K_MA of 1.8 was tentatively proposed as a more plausible value in these waters. Models V and VI gave very similar fits to the data after optimization of DOMFA, in contrast to recent findings for copper. This may be due to the fact that the additional strong binding sites provided by Model VI are not important in complexing Zn in the Zn concentration range investigated in this study. Computed free Zn activities from both modeling scenarios were very similar; however, the consideration of Al and Fe competition is more realistic for natural waters.