Natural Organic Matter Molecules Research Articles

Comparison of the coagulation behavior of different Norwegian aquatic NOM sources

The coagulation behavior of eight natural water samples containing natural organic matter (NOM) was investigated to identify parameters influencing the process. The coagulation of original water samples is discussed using colour and colloidal charge composition in various molecular weight fractions. Over 40% of colours are given by NOM fractions with molecular weight cut-off (MWCO) < 10 kD with one exception. About 1/3 of the colour is given by MWCO fractions > 50 kD for all waters. The optimum coagulant dosage and the colloidal charge were shown to be proportional to the initial colour. This is also valid for dissolved organic carbon (DOC) and for UV-absorbency, which had correlations with colour of R 2 = 0.92 and 0.94, respectively. Larger NOM molecules required fewer amounts of coagulants per removed colour unit compared with smaller NOM molecules. However, it was not possible to show that the NOM molecule size influences the colloidal charge per colour unit. Zeta potentials at optimum coagulant dosages deviate from zero, indicating the presence of other coagulation mechanisms than charge neutralisation. Thus, it is difficult to use zeta potential as the only tool for online dosing coagulant control strategies.

Competitive adsorption in natural water: role of activated carbon pore size

The impact of pore size on the competition mechanism between natural organic matter (NOM) in Illinois groundwater and the micropollutant atrazine was assessed using activated carbon fibers (ACFs). Two microporous ACFs with narrow and broad pore size distributions, designated ACF-10 and ACF-25, respectively, were used. The average pore sizes of ACF-10 and ACF-25 were 6 and 13.4 Å. Single solute adsorption, simultaneous adsorption and preloading experiments were performed. On ACF-10 it was found that the adsorption of atrazine was reduced significantly in the presence of NOM, even though the NOM loading was very small as a result of pore exclusion. The uptake of atrazine by ACF-10 in the presence of NOM (simultaneous adsorption) was comparable to the NOM-preloaded capacity. In addition, preloaded atrazine was not displaced by subsequently adsorbed NOM. The results support a pore blockage mechanism by which NOM molecules block access to, but do not penetrate into the primary micropores. Atrazine capacity on ACF-25 which has primary micropores as well as a large volume of secondary micropores, was reduced in the presence of NOM; however, the reduction in capacity was much less than that observed with ACF-10. Preloading with NOM showed further capacity reduction compared with simultaneous adsorption. These results combined with the result that preloaded atrazine exposed to NOM showed displacement of atrazine support a direct site competition mechanism in the secondary micropore region. Attempts to regenerate NOM preloaded ACF-10 and ACF-25 using a strong alkali solution failed to recover atrazine capacity, suggesting that NOM was strongly adsorbed at the fiber surface as well as within micropores.

Influence of physical-chemical characteristics of natural organic matter (NOM) on coagulation properties: An analysis of eight norwegian water sources

Coagulation behaviour of eight natural water samples containing NOM is investigated to identify parameters influencing the process. A strong correlation between colour, DOC and UV-abs. was shown, regardless of the source and fractions. Coagulation of original water samples is discussed using analytical parameters in raw water and various molecular weight fractions. Over 40% of colour is given by NOM fractions with molecular weight cut-off (MWCO) 50 kD for all waters. Larger NOM molecules required less coagulants per removed colour unit compared with smaller NOM molecules. Bulk NOM parameters and colloidal charges were identified to be the most descriptive parameters of the samples and the coagulability. The possibility to predict the optimum coagulant dosage for given process conditions is illustrated.

Adsorption of natural organic matter (NOM) on iron oxide: Effects on NOM composition and formation of organo-halide compounds during chlorination

A large fraction of the natural organic matter (NOM) in potable water sources can be extracted by adsorption onto iron-oxide-coated sand (IOCS). In this research, two water sources were characterized with respect to their hydrophobic/hydrophilic fractionation, their 13C NMR and UV absorbance spectra and their reactivity with chlorine, before and after the waters were contacted with IOCS. The IOCS preferentially adsorbs acidic fractions of NOM and NOM molecules that are enriched in aromatic and carboxylic carbon. The yield of chloro-organic compounds (quantified as total organo-halide) produced upon chlorination of the NOM or its major fractions correlates with the specific absorbance ( A s) at 254 nm. IOCS may be useful for removing disinfection by-product (DBP) precursors from potable waters and/or as a medium for NOM accumulation.

Iron oxide adsorption and UF to remove NOM and control fouling

Addition of iron oxide particles to a UF system can significantly increase NOM removal efficiency, slowing membrane fouling.This study applied a novel single‐fiber membrane module to study fouling of ultrafiltration (UF) membranes by natural organic matter (NOM) molecules, and used a combined iron oxide–UF process to reduce that fouling. Addition of iron oxide particles to a UF system can significantly increase NOM removal efficiency, because NOM molecules that would otherwise pass through the membrane sorb to the oxides and are retained. Furthermore, despite the fact that iron oxide particles cannot selectively adsorb foulant molecules, their presence in the system can reduce the membrane fouling dramatically. This effect is mediated through two processes: a decrease in the NOM concentration in the circulation loop because of sorption and the formation of iron oxide cake layer deposits on the membrane surface. In such a system, the condensed layer of NOM forms on top of the cake, protecting the underlying membrane surface.

Adsorption of natural organic matter onto goethite

The factors influencing the association of two natural organic matter (NOM) samples (from Redwater Creek in Australia and Suwannee River in USA) with goethite were studied. Sorption occurred very rapidly (minutes) and at very low NOM concentrations (about 0.5 mg C 1 −1), implying that mineral surfaces in the natural aquatic environment would not remain uncoated by NOM for long. The sorption behaviour of the two NOM samples followed the Langmuir adsorption equation. The maximum sorption density for the unfractionated Redwater Creek NOM was 1.1 μmol C mg −1 of goethite. The hydrophobic fractions (both acidic and neutral) separated from the Redwater Creek sample had much greater sorption affinities for the goethite surface than did the hydrophilic fraction. Calculation of the surface crowding indicates that a monolayer of sorbed NOM exists over the goethite surface. Sorption was influenced by solution pH and calcium ion concentration. Maximum sorption density occurred at around pH 3–4, and decreased at higher pH. The sorption density of NOM also appears to be influenced by the presence of non-ionic hydrophobic solutes. This component could shield the electrostatic repulsive forces between neighbouring adsorbed anionic NOM molecules on the goethite surface, thus leading to an increase in the maximum amount of NOM adsorbed. Calcium ion concentration increased sorption of NOM up to calcium concentrations of around 1 mM but higher calcium concentrations resulted in reduced sorption. Sorption of the hydrophobic acid fraction was most affected by calcium concentration. The main effect of NOM sorption on the surface characteristics of goethite is alteration of the surface charge. The isoelectric point of the NOM-coated goethite is shifted markedly to lower pH, compared to that of uncoated goethite. Thus, at the normal pH of natural waters, NOM-coated goethite has a net negative charge which would significantly influence the types of interaction occurring at the surface of the NOM-coated particles in natural aquatic systems. The model advanced for suspended particulate matter (SPM) in aquatic systems, namely a mineral core with coatings of hydrous metal oxides and NOM, appears to explain adequately many aspects of the behaviour of natural SPM.

Catalysis of picolinate ester hydrolysis at the oxide/water interface: inhibition by adsorbed natural organic matter

Natural organic matter (NOM) has been found to inhibit TiO 2 -catalyzed hydrolysis of methyl picolinate (MEP), which is used to represent a broader class of hydrolyzable pollutants. NOM must adsorb at the oxide/water interface in order for inhibition to take place. At equal NOM surface coverage (in mg C/m 2 ), a nearly 60% variation is observed among NOM samples from five different sources. As NOM-laden water poses through soils and sediments, surface-active NOM molecules are removed by adsorption. This fractionation process has been simulated in the laboratory by pretreating a NOM sample with TiO 2 , FeOOH, and Al 2 O 3 - FeOOH is extremely efficient at removing the NOM subfraction responsible for the inhibitory effect, while Al 2 O 3 is the least efficient of the three oxides

Effect of Preozonation on Coagulant–NOM Interactions

Preozonation of water sources containing natural organic matter (NOM) may alter coagulant requirements, the total organic carbon (TOC) removed by coagulation, and the concentration of aluminum and iron in the finished drinking water. In this work, these phenomena were investigated and interpreted as resulting from (1) changes in the zeta potential of precipitates (floes) that form in the presence of ozonated NOM; (2) slight losses of TOC by oxidation and volatilization of NOM molecules; and (3) changes in the quantity of TOC removed by precipitation and sorption.