The behavior of an 18-1 pilot-scale photocatalytic reactor has been investigated using a computational fluid dynamic (CFD) approach. The granular Eulerian model was used to describe the multiphase flow system. Solid recirculation was predicted while liquid velocity vectors were influenced by the gas flow. The companion radiation transport equation was iteratively solved using a finite-volume-based discrete ordinate method. The first-order photodegradation kinetics of spent Bayer liquor previously studied in the same reactor was used to evaluate the CFD simulation. A Pearson correlation coefficient 0.974 between simulated and experimental data is indicative of model adequacy. (C) 2003 Elsevier Science Ltd. All rights reserved.