Nature Of Natural Organic Matter Research Articles

Comparison of Three Solid Phase Materials for the Extraction of Carboxylic Acids from River Water Followed by 2D GC × GC-TOFMS Determination.

The extraction and determination of aliphatic and aromatic carboxylic acids as well as their influence on the aromaticity and molecularity relationship of natural organic matter (NOM) in water are reported in this study. Three solid phase extraction (SPE) sorbents were used and their extraction efficiencies evaluated after chromatographic determinations (using gas chromatography with a time of flight mass spectrometer (GC × GC-TOFMS) and liquid chromatography with organic carbon detector (LC-OCD)). More than 42 carboxylic acids were identified in raw water from the Vaal River, which feeds the Lethabo Power Generation Station, South Africa, with cooling water. The aromatic carboxylic acid efficiency (28%) was achieved by using Strata™ X SPE while the highest aliphatic carboxylic acid efficiency (92.08%) was achieved by silica SPE. The hydrophobic nature of NOM in water depends on the nature of organic compounds in water, whether aromatic or aliphatic. The LC-OCD was used to assess the hydrophobicity levels of NOM as a function of these carboxylic acids in cooling water. The LC-OCD results showed that the aromatic nature of NOM in SPE filtered water followed the order Silica>Strata X>C-18. From the results, the hydrophobicity degree of the samples depended on the type and number of carboxylic acids that were removed by the SPE cartridges.

Comparative Study of the Effect of Vacuum-Ultraviolet Irradiation on Natural Organic Matter of Different Sources

Natural organic matter (NOM) present in surface water sources undergoes significant structural and chemical changes during the application of vacuum ultraviolet (VUV)–based advanced oxidation process (AOP), which leads to the formation of undesired by-products such as aldehydes. Partial NOM mineralization can occur depending on the fluence received. In this paper, the VUV-induced degradation of NOM and the subsequent formation of by-products were experimentally studied. Two natural waters (Trepanier Creek and Capilano Reservoir, in British Columbia, Canada) and two synthetic waters (Suwannee River, Southern Georgia and Northern Florida; Nordic Reservoir, Vallsjøen, Skarnes, Norway) were used. While the process started with partial oxidation of NOM, extensive irradiation (i.e., high UV+VUV fluence) led to complete mineralization of NOM. The rates of mineralization were greatly dependent on the nature of NOM and on the presence of inorganic compounds in the water matrix, such as carbonates and bicarbonates. A faster mineralization rate was obtained with waters containing NOM with a lower average molecular weight. Size exclusion chromatography analysis showed that high-molecular-weight (HMW) molecules were readily degraded, even from the beginning of the treatment. The fraction of low-molecular-weight (LMW) compounds also reduced, but at a slower rate, largely because LMW compounds were both formed through partial degradation of HMW compounds and degraded by hydroxyl radicals. The concentration of aldehydes and trihalomethane formation potentials increased up to 120–700 ppb, respectively, after receiving a UV+VUV fluences in the range of 1–3 J cm−2), but decreased with relatively higher UV+VUV fluencies (>4 J cm−2).

Abiotic formation of methyl iodide on synthetic birnessite: A mechanistic study

Methyl iodide is a well-known volatile halogenated organic compound that contributes to the iodine content in the troposphere, potentially resulting in damage to the ozone layer. Most methyl iodide sources derive from biological activity in oceans and soils with very few abiotic mechanisms proposed in the literature. In this study we report that synthetic manganese oxide (birnessite δ-MnO2) can catalyze the formation of methyl iodide in the presence of natural organic matter (NOM) and iodide. Methyl iodide formation was only observed at acidic pH (4–5) where iodide is oxidized to iodine and NOM is adsorbed on δ-MnO2. The effect of δ-MnO2, iodide and NOM concentrations, nature of NOM and ionic strength was investigated. High concentrations of methyl iodide were formed in experiments conducted with the model compound pyruvate. The Lewis acid property of δ-MnO2 leads to a polarization of the iodine molecule, and catalyzes the reaction with natural organic matter. As manganese oxides are strong oxidants and are ubiquitous in the environment, this mechanism could significantly contribute to the global atmospheric input of iodine.

The response of typical South African raw waters to enhanced coagulation

Drinking water treatment plants in South Africa rely almost entirely on surface water sources, which are often compromised due to high return flows and indirect reuse. The typical treatment plants focus on the removal of physical and microbial contaminants which include turbidity, colour, chemical compounds and microorganisms. A relatively new concern to this list is natural organic matter (NOM) which has become a major concern in potable water treatment due to its recent regulation. In this study, eight different raw water samples from the various water types found in the country were seasonally collected and treated for the removal UV absorbance at a wavelength of 254 nm (UV254) using enhanced coagulation (EC). The efficacy of EC, which can be employed as a practical technology in the removal of both turbidity and NOM, was evaluated in remaining UV254 from these raw water sources. Jar tests were conducted, with ferric chloride used as the coagulant (due to its extensive use as a coagulant in the water treatment industry in South Africa) and specific pH values (initial water pH, 7.0, 6.0, 5.5, 5.0 and 4.5) were chosen as target values guiding the six different coagulant dosages for the jar tests. The pH of the low-alkalinity (<60 mg/L CaCO3) raw waters were adjusted and raised by the addition of sodium carbonate. The response parameters of the tests were turbidity (NTU), pH and UV254. Algorithms for finding the optimum coagulant dosage for UV254 removal were developed and consistently applied to all the results. Results showed large variations in the nature of NOM across the country from specific ultraviolet absorbance values. From the UV254 values, the concentrations of NOM also varied greatly geographically than temporally. The general trend observed in the EC results suggested that the pH should always be dropped to between 4.5 and 7.0 to lower the amounts of UV254 and turbidity to reasonable levels.

Using Parametric and Nonparametric Methods to Model Total Organic Carbon, Alkalinity, and pH after Conventional Surface Water Treatment

Abstract Predicting the behavior of natural organic matter (NOM), alkalinity, and pH during drinking water coagulation is difficult because of the heterogeneous chemical nature of NOM and the complexity of carbonate chemistry. Parametric and nonparametric statistical regression methods were implemented to model the removal of NOM, as measured by total organic carbon (TOC), from raw water by conventional surface water treatment and to track the behavior of pH and alkalinity. The United States Environmental Protection Agency (U.S. EPA) Information Collection Rule (ICR) database was sampled for raw water and postsedimentation data from conventional surface water plants. All models were evaluated in terms of their fit and predictive capability, and for all variables explored, the nonparametric local polynomial models outperformed their parametric linear least-squares counterparts. This was most pronounced with the pH model, and was attributed to the nonlinear relationship found between pH and one of the predi...

Controversies about the occurrence of chloral hydrate in drinking water

Besides trihalomethanes (THMs) and haloacetic acids (HAAs), chloral hydrate (CH) is the next most prevalent disinfection by-product (DBP) in drinking water, formed as a result of the reaction between chlorine and natural organic matter (NOM). Chloral hydrate (trichloroacetaldehyde) should be limited in drinking water because of its adverse health effect. The controversies concerning the appearance of CH in disinfected water found in literature are discussed in the present paper. According to some authors the CH yield during chlorination of water depends only on TOC. However, there are other data available that do not confirm this relationship. Another fact requiring clarification is the dependence of CH formation on pH. In the present study, CH formation is analysed in different types of water disinfected with different doses of chlorine. Formation of CH is correlated with the dose of Cl 2 and the contact time. The formation of chloral hydrate takes place as long as chlorine is available in the water. Total organic carbon (TOC) is not considered the main factor influencing the production of chloral hydrate in water treated with Cl 2 as the production depends also on the nature of NOM. Higher levels of CH are observed at alkaline conditions (pH > 7). A significant correlation ( R 2 > 0.9) between the concentrations of chloral hydrate and chloroform has been observed. The preozonation increases significantly the chloral hydrate formation potential in the water treated. Biofiltration process does not remove all of CH precursors and its efficiency depends strongly on the contact time. Chloral hydrate was analyzed by gas chromatography with electron capture detector with the detection limit 0.1 μg L −1.