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The radiation field in an annular photocatalytic reactor is simulated using a Monte Carlo method (MC) for two TiO 2 suspensions in water. Simulations are performed by using both the spectral distribution and the wavelength-averaged scattering and absorption coefficients. The Henyey-Greenstein phase function is adopted to represent forward, isotropic, and backward scattering modes. It is assumed that the UV lamp reflects the backscattered photons by the slurred medium. Photoabsorption rates using MC simulations and spectral distribution of the optical coefficients agree closely with experimental observations from a macroscopic balance. It is found that the scattering mode of the probability density function is not a critical factor for a consistent representation of the radiation field. MC simulation for the optimal catalyst concentration reveals that the maximum LVREA is reached at a concentration of 0.14 g L -1 for TiO 2 Degussa P25. From this concentration, the apparent optical thickness is determined to be 2.8476 which is in agreement with the optimal one previously reported. This concentration is comparable to that determined experimentally for phenol photocatalytic degradation.

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Photocatalytic conversion of a model pollutant (methylene blue) is studied in a novel Photo-CREC reactor unit. The experiments developed allow us to investigate the suitability of an heterogeneous reaction model which accounts for the concentrations of the model pollutant both in the bulk and on the mesh-TiO 2 . In addition, a photochemical-thermodynamic efficiency factor (PTEF) is further examined, with the help of the enthalpy of • OH formation from water and oxygen and based on the analysis in the light energy absorbed by the mesh. The resulting PTEF is a dimensionless parameter and has to be calculated at high enough model pollutant concentrations, that is, at conditions where zero-order reactions prevail. The PTEF values found in the Photo-CREC unit with the incorporated recent technical improvements are in the 0.0182 level, and this represents quantum yields of 6.31% of the so-called ideal efficiency.