Electron Pulse Radiolysis Determination of Hydroxyl Radical Rate Constants with Suwannee River Fulvic Acid and Other Dissolved Organic Matter Isolates
Department of Civil and Environmental Engineering, Arizona State University, Box 5306, Tempe, Arizona 85287-5306, USA.Environmental Science and Technology (Impact Factor: 5.33). 08/2007; 41(13):4640-6. DOI: 10.1021/es062529n
Pulse radiolysis experiments were conducted on dissolved organic matter (DOM) samples isolated as hydrophobic and hydrophilic acids and neutrals from different sources (i.e., stream, lake, wastewater treatment plant). Absolute bimolecular reaction rate constants for the reaction of hydroxyl radicals (*OH) with DOM (k*(OH), DOM) were determined. k*(OH, DOM) values are expressed as moles of carbon. Based on direct measurement of transient DOM radicals (DOM*) and competition kinetic techniques, both using pulse radiolysis, the k*(OH, DOM) value for a standard fulvic acid from the Suwannee River purchased from the International Humic Substances Society was (1.60 +/- 0.24) x 10(8) M(-1) s(-1). Both pulse radiolysis methods yielded comparable k*(OH, DOM) values. The k*(OH, DOM) values for the seven DOM isolates from different sources ranged from 1.39 x 10(8) M(-1) s(-1) to 4.53 x 10(8) M(-1) s(-1), and averaged 2.23 x 108 M(-1) s(-1) (equivalent to 1.9 x 10(4) (mgC/L)(-1) s(-1)). These values represent the first direct measurements of k*(OH, DOM,) and they compare well with literature values obtained via competition kinetic techniques during ozone or ultraviolet irradiation experiments. More polar, lower-molecular-weight DOM isolates from wastewater have higher k*(OH, DOM) values. In addition, the formation (microsecond time scale) and decay (millisecond time scale) of DOM* transients were observed for the first time. DOM* from hydrophobic acids exhibited broader absorbance spectra than transphilic acids, while wastewater DOM isolates had narrower DOM* spectra more skewed toward shorter wavelengths than did DOM* spectra for hydrophobic acids.
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- "The measured value of k AMZ, OH was 2.05 · 10 10 L/ mol$s; in contrast, k AMZ,1O2 was found to be much lower (*5 · 10 6 L/mol$s), which indicates that singlet oxygen plays a less important role in AMZ degradation. Conversely, the effective diffusion controlled value of k AMZ, OH compared with the value of the rate constant for the reaction between NOM and OH radical (about 10 8 –10 9 mol/L$s) suggests that this pathway may be more important (Buxton et al., 1988; Westerhoff et al., 2007; McKay et al., 2013). "
ABSTRACT: Amicarbazone (AMZ) is an extensively used, broad-spectrum triazolinone herbicide. The literature is scarce regarding experimental data on AMZ photodegradation, whose fate in natural waters has not yet been inves- tigated in detail. By combining laboratory experiments using isolated natural organic matter, literature data, and mathematical simulations, we investigated the sunlight-driven direct and indirect degradation of AMZ. We show that the reaction with hydroxyl radicals (OH) is the main pathway leading to AMZ degradation, with measured second-order reaction rate constant (kAMZ, OH) equal to 2.05 · 1010 L/mol$s. Simulations suggest that amicarbazone degradation is favored in shallow water bodies containing low dissolved organic carbon (DOC) and bicarbonate/carbonate concentrations, with herbicide half-life varying from about less than 1 day to more than 2 months. These values of t1/2 are upper limits since the reaction with 3CDOM* was not considered. Finally, the cross-effects of water depth/[DOC] are slightly influenced by nitrate/nitrite and bicarbonate/ carbonate concentrations, depending on the pH range.Environmental Engineering Science 07/2015; 32(8). DOI:10.1089/ees.2015.0127 · 0.99 Impact Factor
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- "Dissolved organic matter (DOM) is defined as the organic materials below 0.45 μm or 0.22 μm. In the aquatic environment, DOM has a significant effect on the biogeochemical processes, particle stability and transport, metal complexation in the aquatic systems  . Therefore, it is often utilized as a control parameter in design of the water treatment process as well as others such as water treatment efficiency and the formation of disinfection byproducts (DBPs)  . "
ABSTRACT: DOM is often utilized as a control parameter in the design of water treatment process as well as others such as water treatment efficiency and formation of disinfection byproducts (DBPs), of which removal and characterization have received wide attention. Fluorescence excitation–emission matrix spectroscopy (EEMs) for DOM characterization in flocculation process at present is not well known. It is for this reason that the EEMs in this study was employed to characterize the Missouri River DOM removal by the flocculation process. The results showed that four underlying components extracted from the EEMs of DOM by parallel factor (PARAFAC) were humic acid-like (A), fulvic acid-like (B), protein-like (C) and unidentified component (D), while the Missouri River DOM was dominated by A, B and C. Flocculation was effective for the hydrophobic organic compound A followed by the hydrophilic organic compounds B and C, whereas the smallest molecular size compound C was hard to treat. Further study illustrated that for flocculation at pH 7, higher DOC and THM removal efficiencies were obtained, and that the correlations of DOM components with DOC and THM removal efficiencies were significant, thus indicating that the EEMs-PARAFAC offers a robust analytical method for assessing DOM removal efficiency in the flocculation process.Desalination 08/2014; 346:38–45. DOI:10.1016/j.desal.2014.04.031 · 3.76 Impact Factor
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- ". Limited information is available on the reaction rate constant of natural organic matter (NOM) with SO 4 @BULLET− . However, its reactivity is expected to be at least one order of magnitude lower than k HO • /NOM  . Besides, under UV-254 nm irradiation, S 2 O 8 2− has a much higher radical quantum yield than H 2 O 2 , as shown in Eqs. "
ABSTRACT: The extensive production and usage of antibiotics have led to an increasing occurrence of antibiotic residuals in various aquatic compartments, presenting a significant threat to both ecosystem and human health. This study investigated the degradation of selected β-lactam antibiotics (penicillins: ampicillin, penicillin V, and piperacillin; cephalosporin: cephalothin) by UV-254nm activated H2O2 and S2O8(2-) photochemical processes. The UV irradiation alone resulted in various degrees of direct photolysis of the antibiotics; while the addition of the oxidants improved significantly the removal efficiency. The steady-state radical concentrations were estimated, revealing a non-negligible contribution of hydroxyl radicals in the UV/S2O8(2-) system. Mineralization of the β-lactams could be achieved at high UV fluence, with a slow formation of SO4(2-) and a much lower elimination of total organic carbon (TOC). The transformation mechanisms were also investigated showing the main reaction pathways of hydroxylation (+16Da) at the aromatic ring and/or the sulfur atom, hydrolysis (+18Da) at the β-lactam ring and decarboxylation (-44Da) for the three penicillins. Oxidation of amine group was also observed for ampicillin. This study suggests that UV/H2O2 and UV/S2O8(2-) advanced oxidation processes (AOPs) are capable of degrading β-lactam antibiotics decreasing consequently the antibiotic activity of treated waters.Journal of Hazardous Materials 07/2014; 279C:375-383. DOI:10.1016/j.jhazmat.2014.07.008 · 4.53 Impact Factor
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