Oxidation of metal-diethylenetriaminepentaacetate (DTPA)--complexes during drinking water ozonation.
This study investigates the oxidative transformation of diethylenetriaminepentaacetate (DTPA), a synthetic ligand, during drinking water ozonation. The rate coefficients for the reactions of CaDTPA3- and ZnDTPA3- with ozone were determined to be 6200 and 3500 +/- 150 M-1 s-1, respectively. The reactivity of Fe(III)DTPA2- towards ozone was found to be much lower (< 10 M-1 s-1), but near neutral pH the reactivity of the Fe(III)-complexes is dominated by [Fe(III)(OH)]DTPA3-. For the reaction of Fe[(III)(OH)]DTPA3- with ozone a rate coefficient of 2.4 +/- 0.2 x 10(5) M-1 s-1 was measured. The rate coefficients of the reactions of the ZnDTPA- and Fe(III)DTPA with OH radicals have been determined by a competitive method as 2.4 +/- 0.4 x 10(9) and 1.5 +/- 0.1 x 10(9) M-1 s-1, respectively at pH = 7. The degradation of low concentrations of DTPA complexes during ozonation was investigated in natural waters under drinking water relevant conditions. Based on our findings CaDTPA3- and ZnDTPA3- are judged as easily degradable. Fe(III)DTPA complexes showed a somewhat lower reactivity, but were still typically degraded by one order of magnitude at ozone dosages of approximately 20 microM (1 mg L-1) in the three natural waters tested. Molecular ozone was found to be the major oxidant for the metal-DTPA complexes during ozonation.
Stemmler
K
K
EAWAG, Swiss Federal Institute for Environmental Science and Technology, Uberlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Glod
G
G
Von Gunten
U
U
D002614:Chelating Agents / Q000737:chemistry*; D008670:Metals / Q000737:chemistry; D010084:Oxidation-Reduction; D010126:Ozone; D004369:Pentetic Acid / Q000737:chemistry*; D018508:Water Purification / Q000379:methods; D014881:Water Supply
D002614:Chelating Agents; D008670:Metals; D010126:Ozone; D004369:Pentetic Acid