In this study, the rates of degradation of organic compounds by several AOPs (H 2 O 2 /UV, Fe(III)/UV, Fe(III)/H 2 O 2 /UV, Fe(II)/H 2 O 2 and Fe(III)/H 2 O 2 ) have been compared. Experiments were carried out at pH ~ 3 (perchloric acid / sodium perchlorate solutions) and with UV reactors equipped with a low-pressure mercury vapour lamp (emission at 253.7 nm). The data obtained with atrazine ([Atrazine] o = 100 μg/L) showed that the rate of degradation of atrazine in very dilute aqueous solution is much more rapid with Fe(III)/UV than with H 2 O 2 /UV. Photo-Fenton process (Fe(III)/H 2 O 2 /UV) was found to be more efficient than H 2 O 2 /UV and Fe(II)/H 2 O 2 for the mineralization of acetone ([Acetone] o = 1 mM).