Quantification of hydroxyl radical during ozonation in batch system.

Ozonation is widely used in tap water treatment for removal of musty odor. Active species of ozonation are supposed to be molecular ozone and hydroxyl radical. Dissolved materials in water can affect ozonation, but the relation among ozone, hydroxyl radical and dissolved materials have not been quantitatively analyzed. Batch system would be generally applied to investigate ozone reaction. So, in this study, hydroxyl radical formation during ozonation was investigated using spin trap ESR technique in batch system. The results were compared with that obtained using stopped-flow system.In case of methylphenols, amounts of DMPO-OH increased in comparison with that without the phenol and reached a constant value. The enhancement effect was similar to the case in which the stopped flow equipment was used. In case of chlorophenols, amount of DMPO-OH was also enhanced but it decreased in a time dependent manner. Decreases in DMPO-OH were dependent on ozone-concentration. In case of 20μM ozone, DMPO-OH generation in batch and stopped flow system were almost the same, when the enhancing effect was calculated using the Y intercept obtained by extrapolating from elimination curves. However, in higher ozone concentration, enhancing effects of phenols in DMPO-OH formation were underestimated compared with that in stopped-flow system. In conclusion, batch system, in addition with stopped-flow system, would be also useful for analyzing enhancing effects of dissolved compounds on ozone reaction when they have moderate enhancing effects.