Effect of Inorganic Carbon on Ozone Self-Decomposition

Abstract

The effect of inorganic carbon on ozone self-decomposition was examined in this study. Experiments were carried out under a wide concentration range of inorganic carbon of 0–30 mgC/L. First, the rate constant in the overall description model with nth order reaction on dissolved ozone was evaluated. A clear difference in the rate constants with and without inorganic carbon was observed even when the concentration of inorganic carbon was as low as 3 mgC/L; the difference with and without inorganic carbon was almost one order of magnitude. Reaction rate constant was lower with an increase of inorganic carbon concentration. The reaction rate constants were in the range from 1.4 × 10−5–1.9 × 10−4 (mg/L)−1sec.−1 under pH of 6.8–8.1 and inorganic carbon concentration of 6–30 mgC/L and converged on the order of 1.0 × 10−4 (mg/L)−1sec.−1. The difference of the second-order reaction rate constant under the practical range of pH and inorganic carbon concentration was one order of magnitude at most. Depression of ozone self-decomposition rate by inorganic carbon was also evaluated as a scavenging rate by inorganic carbon species against hydroxyl radical. Although the profile of scavenging rate constant was complex, the order of scavenging rate was 102 sec−1 at most in the practical range of pH and inorganic carbon concentration. Because the overall effect of inorganic carbon species on hydroxyl radical scavenging was evaluated qualitatively, the depression extent on ozone self-decomposition, as well as scavenging extent on hydroxyl radical by inorganic carbon is able to be analyzed qualitatively.