In this study, TiO2/SiO2 beads packed bed reactor system in which black light was placed at the center of the reactor was developed for a low cost and environmentally-friendly water treatment process. The reactor was designed to achieve efficient utilization of UV light, large contact area with pollutants as well as easier post separation at the same time. As model pollutants, PNP and DNP were used in this study, and the effects of the initial concentration of those substrates and radial thickness of the packed bed for the decomposition properties were examined. The results showed that the decomposition ratio decreased with the increase of the initial concentration and the packed bed radial thickness. The result suggested that the UV light was absorbed by the solution and TiO2/SiO2 beads. To take into consideration the effect of light absorption toward radial direction of the reactor on the decomposition ratio, simple model called "2-boxes model" was developed. The result of reaction kinetics analysis showed that the 2-boxes model could reasonably explain the experimental data. Finally, by using 2-boxes model, the effective diameter of penetrated UV light was examined. The result confirmed that it decreased with the increase of UV absorption caused by the increase of initial inlet concentration and the increase of the radial thickness of the packed bed. This indicates that the simple 2-boxes model can approximately estimate the effective diameter of packed bed for PNP or DNP decomposition, and it will give a design guideline for an efficient TiO2/SiO2 beads packed bed reactor system for water treatment. (C) 2014 Elsevier B.V. All rights reserved.