In this study, the degradation of high concentrated azo dye solutions was investigated by innovative hybrid process of hydrodynamic cavitation (HC) and photocatalysis in a pilot reactor. HC, photocatalytic, HC + UV and HC + photocatalytic processes were studied for decolorization of RR180 dye solutions. HC + photocatalysis together showed better mineralization at 5 bar of inlet pressure compared to stand-alone HC and photocatalysis. Synergetic coefficients were calculated for COD and TOC removal as 1.48 and 1.17, respectively. TiO2 and ZnO were tested as catalyst type for the hybrid process and ZnO was selected for further experiments on account of better color, COD and TOC removals. Different catalyst loading (0.5-1.5 g/L) was also investigated and 1 g/L of ZnO was found as an optimal loading amount. Increasing initial RR180 dye concentration resulted in decreasing degradation efficiency. Additionally, degradation of different azo dye solutions with two different chemical structures (reactive and direct dyes) was examined with optimum conditions. Tandem operating of hydrodynamic cavitation and photocatalytic processes was efficiently exposed for the treatment of recalcitrant textile dye effluents. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.