The degradation of Alizarin Red S (ARS) was carried out by heterogeneous advanced photo Fenton processes (HAPFP) of the type Fe-0/H2O2/UV and heterogeneous modified photo Fenton process (HMPFP) of the type Fe-0/ammonium persulfate (APS)/UV. The influence of various reaction parameters like pH, catalyst loading, concentration of the oxidants and the influence of inorganic anions such as Chloride (Cl-) and Sulfate (SO42-) ions on processes were investigated. Quenching of the hydroxyl radical by inorganic anions was confirmed by the decrease in the degradation rate constant for the HAPFP from 3.33 x 10(-2) to 0.19 x 10(-2) (for Cl- (1 M)) and 0.29 x 10(-2) min(-1) (for SO42- (1 M)). Similar decrease in rate constant for HMPFP is from 4.67 x 10(-2) to 0.41 x 10(-2)(for Cl- (1 M)) and 0.51 x 10(-2) min(-1) (for SO42- (1 M)) process. The combined effect of concentration of sulfate and chloride ions on the rate constant for the degradation of ARS with APS and H2O2 as oxidants is investigated. The initial degradation mechanism involves the cleavage of a quinone group to catechol as detected by UV-visible and GC-MS analysis. (C) 2013 Elsevier B.V. All rights reserved.