KINETIC AND MECHANISTIC ASPECTS OF THE OXIDATION OF CHLOROPHENOLS BY OZONE

In Advanced oxidation processes (AOPs) radicals are considered to play an important role. Organic contaminations can in AOPs generally be co nverted to carbon dioxide, water, etc, The most important limitation t o the application of AOPs, however, is their high costs, especially wh en complete mineralisation of the pollutants is pursued. The costs can be reduced by using the oxidant more efficiently, which can be achiev ed by introducing selectivity. Kinetic and mechanistic data are the ba sic requirements for optimization of the process. In this work, the in fluence of several different parameters (temperature, pH, UV irradiati on and carbonate concentration) on the kinetics of the degradation of ortho-chlorophenol and para-chlorophenol by ozone was investigated. Th e pH is the most important parameter. Strongly related to the pH is th e degree of ionisation of the phenol, which might be of importance sin ce the shift from a slow to a fast reaction occurs at a higher pH in t he case of para-chlorophenol as compared to the case with the more aci dic ortho-chlorophenol. A strong indication for a radical mechanism is found in the decrease of the reaction rate in the presence of carbona te, a well known radical scavenger. A further indication is seen in th e first step of the reaction, which is dechlorination of the aromatic compound. (C) 1997 IAWQ, Published by Elsevier Science Ltd.