Elimination pathways during water ozonation of volatile organochlorine compounds

Abstract

Ozonation of trichloroethylene, TCE and 1,1,1 trichloroethane, TCA in water has been studied. The effect of gas flow rate, pH, ozone partial pressure and water nature has been investigated. These variables exert positive effects on the elimination rates. Gas flow rate effect is specially important in the case of TCA which, at 20 Lh‐1, is mainly transferred from the water to the air rather than being decomposed through ozonation. On the contrary, TCE is mainly oxidised through hydroxyl radicals. The rate constant of the TCE‐ozone direct reaction was found to be 17.1 M‐1s‐1 which confirms that direct ozonation represents a rather poor contribution (in most cases between 2 to 5%) of the total TCE elimination rate. Therefore, ozonation of these compounds is basically an advanced oxidation process due to the participation of hydroxyl radicals. At high gas flow rates (20 Lh‐1) ozonation rates of VOC elimination were similar in ultrapure laboratory and surface waters used, except for the case of TCE that at 2.5 Lh‐1 gas flow rate, decomposes in ultrapure water faster than in surface water.