DEGRADATION OF 4-CHLOROPHENOL BY ANODIC-OXIDATION, ELECTRO-FENTON, PHOTOELECTRO-FENTON, AND PEROXI-COAGULATION PROCESSES

The degradation of 4-chlorophenol in acidic solution of pH similar to 3.5 has been studied by different electrochemical methods involving H2 O2 electrogeneration from an O-2-diffusion cathode. While the solution is slowly mineralized by anodic oxidation in the presence of H2O2, th e rate for organic carbon removal increases notably by electro-Fenton, photoelectro-Fenton, and peroxi-coagulation, where Fe2+ acts as catal yst to produce oxidizing OH. from electrogenerated H2O2. A complete mi neralization was only reached in the photoelectro-Fenton process. For peroxi-coagulation, the removal of organic carbon in solution is mainl y due to the coagulation of dechlorinated intermediates with the Fe(OH )(3) precipitate formed. The decay for substrate concentration is fast er by electro-Fenton and photoelectro-Fenton than by peroxi-coagulatio n. In all methods, the initial hydroxylated intermediate is 4-chloro-1 ,2-dihydroxybenzene, which is further oxidized with loss of chloride i on to yield maleic and fumaric acids. Fe3+ complexes are produced in t he processes using iron ions. These complexes are slowly mineralized b y electro-Fenton and rapidly photodecomposed to CO2 by photoelectro-Fe nton processes. The apparent current efficiencies for the mineralizati on processes have been determined. A general pathway for the degradati on of 4-chlorophenol by the different methods studied is proposed.