Heterogeneous Fenton type processes using Fe-exchanged zeolite of ZSM5 type were investigated for the degradation of model organic pollutant, reactive azo dye C.I. Reactive Blue 137, in water. Research work was directed to compare process efficiency and to establish their advantages over corresponding homogenous Fenton type processes. The influence of UV irradiation on both heterogeneous and homogeneous processes was also studied. On the basis of decolorization and mineralization degree of dye aqueous solution the overall process efficiency was estimated. Homogeneous and heterogeneous Fenton processes yielded similar decolorization and mineralization, but the concentration of Fe ions in the bulk after the treatment was significantly lower in the latter case. Moreover, the usage of heterogeneous catalyst allows process to be operated at milder pH conditions minimizing the addition of counter ions (both anions and cations) for strong pH conditioning like in homogeneous Fenton processes. Besides that, another advantage of heterogeneous over homogeneous process is the avoidance of unnecessary additional loading of wastewater by counter ions that originated from iron salts. UV irradiation positively affected both decolorization and mineralization degree in all applied homogeneous and heterogeneous Fenton type processes. (C) 2010 Elsevier B.V. All rights reserved.