A reactive transport model was developed to simultaneously predict Cryptosporidium parvuum oocyst inactivation and bromate formation during ozonation of natural water. A mechanistic model previously established to predict bromate formation in organic-free synthetic waters was coupled with an empirical ozone decay model and a one-dimensional axial dispersion reactor (ADR) model to represent the performance of a lab-scale flow-through ozone bubble-diffuser contactor. Dissolved ozone concentration, bromate concentration. (in flow-through experiments only), hydroxyl radical exposure and C. parvum oocyst survival were measured in batch and flow-through experiments performed with filtered Ohio River water. The model successfully represented ozone concentration and C. parvum oocyst survival ratio in the flow-through reactor using parameters independently determined from batch and semi-batch experiments. Discrepancies between model prediction and experimental data for hydroxyl radical concentration and bromate formation were attributed to unaccounted for reactions, particularly those involving natural organic matter, hydrogen peroxide and carbonate radicals. Model simulations including some of these reactions resulted in closer agreement between predictions and experimental observations for bromate formation. (c) 2006 Elsevier Ltd. All rights reserved.