A kinetic study of 3-chlorophenol enhanced hydroxyl radical generation during ozonation

Hydroxyl (OH) radical is proposed as an important factor in the ozonation of water. In the present study, the enhancing effect of 3-chlorophenol on OH radical generation was mathematically evaluated using electron spin resonance (ESR)/spin-trapping technique. OH radical was trapped with a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a stable adduct, DMPO–OH. The initial velocity of DMPO–OH generation in ozonated water containing 3-chlorophenol was quantitatively measured using a combined system of ESR spectroscopy with stopped-flow apparatus which was controlled by home-made software. The initial velocity of DMPO–OH generation increased as a function of the concentration of ozone and the more effectively of 3chlorophenol concentration. The relation among ozone concentration, amount of 3-chlorophenol and the initial velocity ((nu)0 (10^-6M/s)={9.7×[3-chlorophenol (10^-9M)]+0.0005} exp(57×[ozone (10^-9M)]). The equation fitted very well with the experimental results, and the correlation coefficient was larger than 0.99. The equation for the enhancing effect by 3chlorophenol should provide useful information to optimize the condition in ozone treatment process of water containing phenolic pollutants.