Development and modeling of a rotating disc photocatalytic reactor for wastewater treatment

A photon-effective rotating disc photocatalytic reactor configuration was proposed and compared to a similar rotating drum reactor. The photocatalytic degradation of a model non-volatile aromatic compound, 4-chlorophenol, was investigated as a function of rotation speed, angle of disc, and radiation intensity. The irradiance distribution on the surface of the disc/drum was analyzed by a diffuse emission model, which was verified by experimental measurement. The profiles of the predicted local-area-specific rate of energy absorption (LASREA) indicated its sensitivity to the geometrical dimensions. A new kinetic model was proposed including the effects of water film thickness and irradiance. Based on the model and irradiance distribution, a rigorous kinetic analysis was conducted in accordance with mass balance and mass transfer. The experimental data were compared with the mathematical prediction, showing good agreement. With respect to scale-up parameters, the results suggested that the surface velocity, ϕω/2 (ϕ: diameter of the disc, ω: rotation speed) is an important factor which determines the thickness of water film, while diameter and angle of the disc determine the irradiance distribution. The incident photon flow rate has no relation to the angle of the disc, but a small angle will provide a larger illuminated area and capture more reflected photons. Comparatively, the larger illuminated area is much more important than capture of reflected photons for improvement of the photonic efficiency. In the rotating disc reactor, the photon number increased 11.2% due to capture of reflections, and the maximum initial photonic efficiency reached 0.0251 mol-4-CP/einstein, while in the drum reactor it was 0.0145 mol-4-CP/einstein.