Photocatalytic process is a green technology that has been widely used in textile wastewater treatment. Mass transfer phenomenon plays an important role in photoreactor with photocatalyst immobilized on surface. In this study, a novel photocatalytic cascade disc reactor coated with ZnO nanoparticles was first applied to investigate the effect of two influential parameters, i.e. artificial roughness and flow rate on photocatalysis degradation of Reactive Yellow 81 (RY81). Mass transfer coefficients were then determined to describe the effect of those parameters on photocatalytic process based on benzoic acid dissolution method. Fluid flow and concentration fields were simulated to explore the characteristics of mass transfer process with OpenFOAM software. Based on the experimental and simulation results, it was found that as artificial roughness and flow rate value increase, Reynolds number and consequently the first order reaction rate constant of RY81 and mass transfer coefficients significantly increase. (C) 2017 Elsevier B.V. All rights reserved.