In the frame of this work, photo-Fenton processes using the zero-valent iron (ZVI) as a catalyst have been applied for mineralization and decolourization of the model wastewater containing reactive azo dye, C.I. Reactive Black 1 (RB1). Experiments were performed in the enhanced configuration of laboratory cylindrical batch photoreactor under UV-C irradiation (CBPR) and the boat-shaped flow reactor (BSFR) in total recirculation mode, exposed to direct sunlight, both with the immobilized iron. In the first part of the study, optimization of UV-C/ZVI-Fenton process has been performed using the concept of experimental mixture design, whereas Fenton reagent composition (ZVI and H2O2) and pH condition were treated as a three-component mixture. Due to the strict boundaries and constraints of mixture design, a single point in the design space emerged upon each optimization cycle. Corresponding kinetics was studied at optimal conditions. Two approaches has been compared: in the first approach a heterogeneous catalytic pathway has been adopted, while the second approach assumed the pure homogeneous catalysis, exploring the crucial role of the Fe(II) ions in the bulk solution due to its leaching from the ZVI surface. Corrosion of ZVI surface was examined by the means of material characterization and Fe(II) leaching. (c) 2012 Elsevier B.V. All rights reserved.