Contribution of free radicals to chlorophenols decomposition by several advanced oxidation processes

The chemical decomposition of aqueous solutions of various chlorophenols (4 -chlorophenol(4-CP), 2,4-dichlorophenol (2-DCP), 2,4,6-trichlorophenol (2,4 ,6-TCP) and 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP)), which are environmen tal priority pollutants, is studied by means of single oxidants (hydrogen p eroxide, UV radiation, Fenton's reagent and ozone at pH 2 and 9), and by th e Advanced Oxidation Processes (AOPs) constituted by combinations of these oxidants (UV/H2O2, UV/Fenton's reagent and O-3/UV). For all these reactions the degradation rates are evaluated by determining their first-order rate constants and the half-life times. Ozone is more reactive with higher subst ituted CPs while OH . radicals react faster with those chlorophenols having lower number of chlorine atoms. The improvement in the decomposition level s reached by the combined processes, due to the generation of the very reac tive hydroxyl radicals, in relation to the single oxidants is clearly demon strated and evaluated by kinetic modeling. (C) 2000 Elsevier Science Ltd. A ll rights reserved.