A mechanistic kinetic model for the photo-Fenton-like degradation of polyacrylic acid (PAA) is developed and validated using experimental data collected by a batch recirculation photoreactor. The developed mathematical model incorporates all detailed photochemical reactions including Fe2+ and Fe3+ chlorocomplexes, inorganic anion radicals (Cl-2(center dot-) and Cl-), and the polymer degradation. Population balance equations are used for kinetic modeling of the polymer degradation based on the chain-end scission. The proposed model could accurately predict the total organic carbon (TOC) removal rate of nine sets of experimental runs. Sensitivity analysis is also performed to evaluate the most significant kinetic parameters used in the mathematical model. Furthermore, an experimental run is conducted in continuous mode at optimum operating conditions to investigate the computational fluid dynamics (CFD) based on the transport-reaction coupling. The CFD simulation results for the TOC removal are compared with those of the experimental data. The low discrepancy between CFD simulation results and experimental data confirms the reliability of the CFD model. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.