Electron pulse radiolysis determination of hydroxyl radical rate constants with Suwannee River fulvic acid and other dissolved organic matter isolates.
ABSTRACT 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.
- SourceAvailable from: Sarah E. Page[Show abstract] [Hide abstract]
ABSTRACT: Dissolved organic matter (DOM) is involved in numerous environ-mental processes, and its molecular size is important in many of these processes, such as DOM bioavailability, DOM sorptive capacity, and the formation of disinfection byproducts during water treatment. The size and size distribution of the molecules composing DOM remains an open question. In this contribution, an indirect method to assess the average size of DOM is described, which is based on the reaction of hydroxyl radical (HO •) quenching by DOM. HO • is often assumed to be relatively unselective, reacting with nearly all organic molecules with similar rate constants. Literature values for HO • reaction with organic molecules were surveyed to assess the unselectivity of DOM and to determine a representative quenching rate constant (k rep = 5.6 × 10 9 M −1 s −1Environmental Science & Technology 09/2014; · 5.48 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Water treatment is the processing of water to meet or achieve specified goals or standards set by regulatory agencies and end users. New water treatment technologies are being developed that need to be evaluated on a fundamental scientific and practical basis compared to traditional remediation processes. Recent advances in nanomaterial development for water treatment in the areas of filtration membranes, high surface area adsorbents, and efficient photocatalysts require approval for their effectiveness and safeness. Fundamental theories and concepts discussed in this chapter pertain to the areas of (i) adsorption and equilibrium isotherms (ii) pressure-driven membrane filtration and its rejection mechanisms for filtration and reverse osmosis processes; and (iii) advanced oxidation processes with a focus on semiconductor photocatalytic concepts.Nanotechnology for Water Treatment and Purification, Edited by Anming Hu, Allen Apblett, 01/2014: chapter 1: pages 1-45; Springer International Publishing., ISBN: 9783319065779
- The Chemical Engineering Journal 03/2015; 263:45-54.