Oxidation of pesticides in water by Fenton and photo-Fenton reactions

The degradation of four pesticides, namely atrazine (ATZ), fenitrothion (FNT), 4-chloro-2-methyl-phenoxyacetic acid (MCPA) and 4-chlorophenoxyacetic acid (CPA) by Fenton and UVA-induced photo-Fenton reactions was investigated. Experiments were conducted at pH 3-3.5 and various Fe(H) and H2O2 concentrations in the range 0.088-0.45 mM and 1.74-33.2 mM respectively. In general, total organic carbon (TOC) removal increased with increasing oxidant concentration, while the effect of catalyst concentration was less pronounced. ATZ was considerably refractory to total oxidation which can be approached by a two-stage, second order kinetic expression. The other three pesticides were more readily oxidizable than ATZ following pseudo-first order kinetics. UVA irradiation improved substantially the rate of the corresponding dark reaction; for instance, complete TOC removal was achieved after 120 min of FNT photo-Fenton oxidation at 33.2 mM H2O2 concentration, with the respective value for the dark run being 5 5%. For ATZ, the respective values were 75 and 40%.