The reaction kinetics of the photocatalytic oxidation (PCO) of the herbicides isoproturon, simazine and propazine over irradiated TiO2 (Degussa P25) suspensions were studied in multicomponent systems in a laboratory- scale annular photoreactor operated in recirculation batch mode. The multicomponent kinetic model established was then extended to take into account the direct effect of radiation absorbed by the TiO2 photocatalyst in order to obtain intrinsic kinetic parameters independent of the radiation field in the photoreactor. An analysis of the radiation field in the photoreaction space was accomplished using a recently published Six-Flux Radiation Absorption-Scattering model (SFM) to decouple the values of the apparent reaction kinetic constants from the local volumetric rate of photon absorption (LVRPA) in the rate law of PCO of herbicide. The resulting rate laws with explicit dependence on the LVRPA were then used to predict, through accurate reactor modeling, the degradation of the herbicides in an optimal configuration of a flow-through, pilot-scale, falling film photoreactor. In a plant treatment scenario the total operating costs 3 of the PCO of herbicides were calculated to be 3.75 Euro m(-3). (C) 2007 Elsevier B.V. All rights reserved.