DECHLORINATION OF CHLORENDIC ACID WITH OZONE

An experimental study was conducted to investigate the use of ozone to dechlorinate chlorendic acid [1,4,5,6,7,7-hexachlorobicyclo-(2,2,1)-hept-5-ene-2,3-dicarboxylic acid; CAS Number 115-28-6]. The dechlorination and subsequent degradation of chlorendic acid by ozonation is influenced by the pH, applied ozone dose and bicarbonate concentration. A change in the initial chlorendic acid concentration to 50, 100 and 200 mg/l did not influence the rate of degradation of chlorendic acid. Ultraviolet radiation alone also dechlorinated chlorendic acid. Ultraviolet radiation (u.v.) was also shown to greatly enhance the oxidation of chlorendic acid in the presence of ozone. In a typical case, 80% dechlorination of chlorendic acid was obtained in 60 min when using an ozone dose of 125 mg/min ozone at pH 7.4. In addition to the experimental results, a model describing the dechlorination of chlorendic acid is presented. The pseudo-first order rate constants for a two-step model were calculated and ranged from 0.002 to 0.295 min-1 for the first step and 0.008 to 6 x 10(12) min-1 (calculated) for the second step. The magnitude of the rate constants and corresponding rates of dechlorination of chlorendic acid were shown to be dependent upon the production and/or scavenging of hydroxyl radicals in solution. Conditions favoring radicals in solution, such as high pH and the addition of u.v., resulted in much faster dechlorination. The conditions which did not favor radicals, such as low pH and the addition of bicarbonate, resulted in slower dechlorination.