Improved application of ion chromatographic determination of carboxylic acids in ozonated drinking water

Kinetic Modeling-Assisted Mechanistic Understanding of the Catalytic Ozonation Process Using Cu-Al Layered Double Hydroxides and Copper Oxide Catalysts

In this study, copper aluminum layered hydroxides (Cu-Al LDHs) and copper oxide (CuO) were utilized as catalysts for heterogeneous catalytic ozonation (HCO). Target compounds oxalate and formate were used with removal by adsorption and oxidation quantified to elucidate the role of the catalyst in contaminant removal. Oxidation of oxalate mostly occurred on the catalyst surface via interaction of surface oxalate complexes with surface-located oxidants. In contrast, the oxidation of formate occurred in the bulk solution as well as on the surface of the catalyst. Measurement of O₃ decay kinetics coupled with fluorescence microscopy image analysis corresponding to 7-hydroxycoumarin formation indicates that while surface hydroxyl groups in Cu-Al LDHs facilitate slow decay of O₃ resulting in the formation of hydroxyl radicals on the surface, CuO rapidly transforms O₃ into surface-located hydroxyl radicals and/or other oxidants. Futile consumption of surface-located oxidants via interaction with the catalyst surface was minimal for Cu-Al-LDHs; however, it becomes significant in the presence of higher CuO dosages. A mechanistic kinetic model has been developed which adequately describes the experimental results obtained and can be used to optimize the process conditions for the application of HCO.

Mechanistic insights into the catalytic ozonation process using iron oxide-impregnated activated carbon

In the present study, radiolabelled formate was used as a probe compound in order to gain mechanistic insight into the catalytic ozonation process using a commercially available iron oxide-impregnated activated carbon catalyst. We simultaneously analysed the adsorptive and oxidative removal of formate in order to determine the contribution of the catalyst to adsorption and oxidant generation processes respectively. Our results show that the presence of the catalyst enhanced ozone decay as well as the rate and extent of formate oxidation at pH 3.0 compared to that observed in the presence of ozone alone as a result of oxidant generation via O₃-Fe oxide interaction. A reduction in rate and extent of formate oxidation on addition of t-butanol and Cl^- (known hydroxyl radical (^•OH) scavengers under acidic conditions) provides evidence that the oxidant generated during catalytic ozonation at pH 3.0 is ^•OH. Moreover, the oxidation of formate during catalytic ozonation mostly occurs at the solid-liquid interface and/or in bulk solution with adsorption playing no role in the overall oxidation process with this finding supported by the exceptionally high oxidation efficiency compared to the extent of adsorption observed when no O₃ was added. While catalytic ozonation was effective in formate oxidation at pH 3.0, the presence of the catalyst did not lead to an increase in either the rate or extent of formate oxidation at pH 7.3 and 8.5 suggesting that only protonated iron oxide surface sites generate strong oxidant(s) on interaction with O₃. Based on our understanding of the processes operating during the ozonation and catalytic ozonation processes, a mathematical model has been developed that adequately describes the experimental results obtained here. Overall, this study shows that systematic measurement of ozone decay, removal of the parent compound as well as formation of the oxidized products under well controlled conditions are required for unequivocal elucidation of the mechanism of catalytic ozonation.

Trends in Ozonation Disinfection By-Products—Occurrence, Analysis and Toxicity of Carboxylic Acids

Ozonation is becoming a common disinfection method for drinking water treatment. This has prompted the investigation of ozonation disinfection by-products (ODBPs) in drinking water. Ozonation generates a diverse range of carbonyl disinfection by-products, including carboxylic acids, aldehydes, ketones and aldo-ketoacids. Among these ODBPs, carboxylic acid by-products (CABPs) are observed in higher concentrations compared to other carbonyl by-products. However, relatively little research has been conducted on CABPs, including their precursors, formation and occurrence, methods of detection and toxicity. This review outlines the occurrence and variability of CABPs in a number of water sources treated and disinfected with ozonation. It considers the effect of ozonation parameters, including ozone dose, temperature and time of ozonation on the formation of CABPs. The review also discusses the various analytical approaches for CABP quantification, as well as their possible toxicity in drinking water.

Simultaneous and sensitive analysis of aliphatic carboxylic acids by ion-chromatography using on-line complexation with copper(II) ion

A new approach to ion chromatography is proposed to improve the UV detection of aliphatic carboxylic acids separated by anion-exchange chromatography. When copper(II) ion added to the mobile phase, it forms complexes with carboxylic acids that can be detected at 240 nm. The absorbance was found to increase with increasing copper(II) ion concentration. The retention times of α-hydroxy acids were also found to depend on the copper(II) ion concentration. Addition of acetonitrile to the mobile phase improved the separation of aliphatic carboxylic acids. The detection limits of the examined carboxylic acids (formate, glycolate, acetate, lactate, propionate, 3-hydroxypropionate, n-butyrate, isobutyrate, n-valerate, isovalerate, n-caproate) calculated at S/N=3 ranged from 0.06 to 3 μM. The detector signal was linear over three orders of magnitude of carboxylic acid concentration. The proposed method was successfully applied to analyze aliphatic carboxylic acids in rainwater and bread.

Occurrence of carboxylic acids in different steps of two drinking-water treatment plants using different disinfectants

The occurrence of 35 aliphatic and aromatic carboxylic acids within two full scale drinking-water treatment plants was evaluated for the first time in this research. At the intake of each plant (raw water), the occurrence of carboxylic acids varied according to the quality of the water source although in both cases 13 acids were detected at average concentrations of 6.9 and 4.7 μg/L (in winter). In the following steps in each treatment plant, the concentration patterns of these compounds differed depending on the type of disinfectant applied. Thus, after disinfection by chloramination, the levels of the acids remained almost constant (average concentration, 6.3 μg/L) and four new acids were formed (butyric, 2-methylbutyric, 3-hydroxybenzoic and 2-nitrobenzoic) at low levels (1.1-5 μg/L). When ozonation/chlorination was used, the total concentration of the carboxylic acids in the raw water sample (4.7 μg/L) increased up to 6 times (average concentration, 26.3 μg/L) after disinfection and 6 new acids (mainly aromatic) were produced at high levels (3.5-100 μg/L). Seasonal variations of the carboxylic acids under study showed that in both plants, maximum levels of all the analytes were reached in the coldest months (autumn and winter), aromatic acids only being found in those seasons.

The effects of antibiotic cocktails at environmentally relevant concentrations on the community composition and acetate biodegradation kinetics of bacterial biofilms

Antibiotics and antibacterials are present in water bodies worldwide but little is known about their effects on the biological processes often used to treat water. In this research, the effect of antibiotics on bacterial activity and community structure was investigated by growing biofilms in the presence and absence of a mixture of three compounds (sulfamethoxazole, erythromycin, and ciprofloxacin) in a continuous-flow rotating annular bioreactor fed acetate as a carbon and energy source. Steady-state, surface area-normalized substrate utilization rates for all antibiotic treatments (all at 0.33 μg L(-1), all at 3.33 μg L(-1), and 1 at 3.33 μg L(-1) with the other 2 at 0.33 μg L(-1)) were similar to the control experiments. Higher attached biomass levels in the experiments with ciprofloxacin at 3.33 μg L(-1) resulted in lower steady-state biomass-normalized substrate utilization rates in comparison to other runs. Microbial community analyses via automated ribosomal intergenic spacer analysis revealed significant shifts in community structure for the experiments dosed with the highest concentrations of ciprofloxacin, suggesting that the antibiotic selected for more resistant bacterial strains. The results of this research also suggest that mixtures of antibiotics at the sub-μg L(-1) concentrations typically observed in surface waters are unlikely to affect biological process performance, at least in terms of the degradation of easily assimilable compounds. Conversely, changes to community structure and biofilm quantity might be expected with ciprofloxacin at μg L(-1) concentrations.

Modern approaches to the analysis of disinfection by-products in drinking water

The discovery and study of disinfection by-products (DBPs) of health and regulatory concern in drinking water have often been hampered by the lack of appropriate analytical methods, but, with the new tools and expertise now available to the drinking water industry, there is an opportunity to plug a major gap in our knowledge of the nature and identity of these chemicals. The challenge is that less than half of the halogenated by-products resulting from the chlorination of drinking water have been identified, and even less is known about those produced in waters treated with ozone, chloramines or chlorine dioxide. For the DBPs that have been identified, very little or no occurrence data exist for the unregulated chemicals to document how often a particular DBP is formed and in what quantity. The elucidation of the nature and identity of these by-products is hindered by two complicating factors. The first is the inherent aqueous solubility of many of these compounds, which renders their efficient extraction from water difficult to achieve. The second is the lack of established identity of specific potential by-products, which complicates targeted analytical approaches. This paper reviews existing and new methodologies that attempt to overcome some of these challenges.

Disinfection byproduct formation and fractionation behavior of natural organic matter surrogates

While natural organic matter (NOM) surrogates are established in disinfection byproduct (DBP) research, their use in fractionation studies is rare. To understand how surrogates relate to drinking waters, a range of NOM surrogates were fractionated with XAD resins. Their trihalomethane (THM), haloacetic acid (HAA), haloacetaldehyde, haloacetonitrile, and haloketone formations after chlorination were recorded. While compounds with higher log K(ow) values behaved as hydrophobic acids, fractionation of the more hydrophilic compounds did not clearly correlate to the log K(ow). High HAA formation from ferulic and aspartic acids and 1,1,1-trichloropropanone (1,1,1-TCP) formation from 3-oxopropanoic acid were notable. Three amino acids, asparagine, aspartic acid, and tryptophan, formed significant levels of dichloroacetonitrile (DCAN) and trichloroacetaldehyde (TCA). Formation of DBPs did not correlate to any compound physical property; however, there were several correlations between DBP groups. The most significant were between dichloroacetic acid (DCAA) and dichloroacetonitrile (DCAN), DCAN and TCA, and dichloroacetaldehyde (DCA) and trichloroacetaldehyde, indicating the possibility of similar relationships in natural waters.

Integrated disinfection by-products mixtures research: disinfection of drinking waters by chlorination and ozonation/postchlorination treatment scenarios

This article describes disinfection of the same source water by two commonly used disinfection treatment scenarios for purposes of subsequent concentration, chemical analysis, and toxicological evaluation. Accompanying articles in this issue of the Journal of Toxicology and Environmental Health describe concentration of these finished waters by reverse osmosis techniques, chemical characterization of the resulting disinfection by-product (DBP) concentrates, in vivo and in vitro toxicological results, and risk assessment methods developed to analyze data from this project. This project, called the "Four Lab Study," involved participation of scientists from four laboratories/centers of the U.S. Environmental Protection Agency Office of Research and Development as well as extramural collaborators from the water industry and academia. One of the two finished waters was prepared by conventional treatment and disinfected by chlorination. The other finished water was also prepared by conventional treatment and disinfected by ozonation followed by chlorination (ozonation/postchlorination). Chlorination conditions of dose, time and temperature were similar for both treatment scenarios, allowing for a comparison. Both finished waters had acceptably low levels of particulates and bacteria, representative pH and chlorine levels, and contained numerous DBP. Known effects of ozonation were observed in that, relative to the water that was chlorinated only, the ozonated/postchlorinated water had lower concentrations of total organic halogen, trihalomethanes (THM), haloacetic acids (HAA), and higher concentrations of bromate, and aldehydes.

Formate as an energy source for microbial metabolism in chemosynthetic zones of hydrothermal ecosystems

Formate, a simple organic acid known to support chemotrophic hyperthermophiles, is found in hot springs of varying temperature and pH. However, it is not yet known how metabolic strategies that use formate could contribute to primary productivity in hydrothermal ecosystems. In an effort to provide a quantitative framework for assessing the role of formate metabolism, concentration data for dissolved formate and many other solutes in samples from Yellowstone hot springs were used, together with data for coexisting gas compositions, to evaluate the overall Gibbs energy for many reactions involving formate oxidation or reduction. The result is the first rigorous thermodynamic assessment of reactions involving formate oxidation to bicarbonate and reduction to methane coupled with various forms of iron, nitrogen, sulfur, hydrogen, and oxygen for hydrothermal ecosystems. We conclude that there are a limited number of reactions that can yield energy through formate reduction, in contrast to numerous formate oxidation reactions that can yield abundant energy for chemosynthetic microorganisms. Because the energy yields are so high, these results challenge the notion that hydrogen is the primary energy source of chemosynthetic microbes in hydrothermal ecosystems.

Biodegradability of organic by-products after natural organic matter oxidation with ClO2--case study

Apart from well-known chlorites and chlorates, chlorine dioxide also generates easily biodegradable carbonyl compounds and short chain carboxylic acids during water disinfection. The main goal of the presented study was to examine the influence of natural organic matter (NOM) oxidation with chlorine dioxide, on the quantity as well as the quality of formed biodegradable by-products. In the experiments conducted at the pilot plant the sand filtered water (MWI) and ozonated/biofiltrated water (BAF) were oxidised with ClO2. The amount of BDOC formed as a result of the oxidation of both waters with ClO2 was compared. The results showed considerable differences in formation of ClO2 oxidation by-products between non-ozonated and ozonated/biofiltered waters. The disinfection of ozonated/biofiltrated water with ClO2 generated comparable amounts of aldehydes and much higher amounts of carboxylic acids than ClO2 oxidation of sand filtered water. These findings are essential for waterworks with ozonation/biofiltration units and ClO2 disinfection implemented.

Formation of aldehydes upon ClO2 disinfection

Carbonyl compounds are considered to be the most common ozonation by-products. Apart from well-known chlorites and chlorates, chlorine dioxide (ClO(2)) also generates organic by-products. The goal of this paper is an investigation into the influence of disinfection with ClO(2) on the aldehydes formation. Three types of waters were disinfected with different doses of ClO(2) at the various pH values. The results of size exclusion chromatography show that the reaction of ClO(2) with humic fraction of natural organic matter proceeds mainly on an aromatic part of the molecules. The results obtained indicate that the level of carbonyls concentration can significantly increase with the time of ClO(2) reaction with carbonyl precursors in treated water. There is no noticeable correlation between quantity of aldehydes and pH value of disinfected water. The range of "productivity" of aldehydes in water treated with chlorine dioxide is similar to the range estimated for the carbonyls formed upon ozonation.

Oxidation of diethylene glycol with ozone and modified Fenton processes

This paper describes a study of oxidation of diethylene glycol (DEG) by ozone and modified Fenton process (hydrogen peroxide and ferric salt mixture) in aqueous solution. Both oxidation processes were able to oxidize relatively high concentrations of DEG effectively. DEG reacted primarily through hydroxyl radical produced by decomposition of ozone, and about 3 mol of ozone were consumed per mole of DEG removed during the process. For modified Fenton oxidation, stepwise addition of hydrogen peroxide (H2O2) and ferric salt (Fe(III)) resulted in much higher removal of DEG than one-time pulse addition of the chemicals. The extent of DEG removal increased with increasing concentrations of both H2O2 and Fe(III). Oxidant consumption per mole of DEG oxidized was one order of magnitude higher for hydrogen peroxide than those observed for ozone. Overall, ozonation produced higher concentrations of aldehydes, and modified Fenton treatment produced higher concentrations of carboxylic acids for the same levels of DEG oxidation. The major products of ozonation were glycolaldehyde, glyoxal, formaldehyde, acetaldehyde, and acetic, formic, pyruvic, oxalic and glyoxalic acids. The major products of modified Fenton oxidation were formaldehyde, and formic and acetic acids.

Combined chemical-biological treatment of wastewater containing refractory pollutants

Biological processes are usually most efficient for degrading pollutants occurring in wastewater. Refractory and toxic compounds contained limit their applicability. In such cases combinations with chemical oxidation processes may improve the overall efficiency and efficacy. Most suitable oxidation processes for combination with biological treatment are wet air oxidation, ozonation, hydrogen peroxide treatment and other advanced oxidation processes. Most effective are OH-radicals produced in all these oxidation processes. Chemical oxidation produces intermediates with usually improved biodegradability. Process combinations may be serial or with recycling between chemical oxidation and biological treatment. Design criteria, control of combined processes and recent applications are reviewed.

Comparative methodology in the determination of alpha-oxocarboxylates in aqueous solution ion chromatography versus gas chromatography after oximation, extraction and esterification

The alpha-oxocarboxylates (alpha-ketocarboxylates) and the corresponding alpha-oxoacids (alpha-ketoacids) have been reported as byproducts of ozonation of potable water supplies. Some of these species also occur in biophysiological systems. Five analytes were investigated in this study: oxoethanoate (glyoxylate), 2-oxopropanoate (pyruvate), 2-oxobutanoate (2-ketobutyrate), 2-oxopentanoate (2-ketovalerate) and oxopropanedioate (ketomalonate, mesoxalate). Ion chromatography (IC) and gas chromatography (GC) were evaluated for the quantitation of these analytes at concentrations < or =200 ng ml(-1). For the IC method, the samples are run directly with minimal to no pre-treatment. For the GC method, the analytes must be derivatized with O-(2,3,4,5,6-pentafluorobenzyl)oxylamine to form oximes. The oximes are extracted into tert-butyl methyl ether and the carboxylic acid is esterified (methylated) with diazomethane. It was concluded that the ion chromatographic determination is significantly superior to the gas chromatographic method for these analytes.