Photocatalysis is an advanced oxidation process and receiving widespread attention in recent times for completely mineralizing organic contaminants in water and air. As a first part of our study, the parameters (dissolved oxygen, catalyst concentration, and light intensity) influencing intrinsic kinetics of phenol degradation is investigated using immersion-well batch reactor with 6 and 125 W UV-A lamps. At high light intensity, dissolved oxygen concentration in the slurry decides the optimum catalyst loading. At low light intensity comparable to that UV intensity of solar radiation, light transmittance into the slurry decides the optimum catalyst loading. Application of photocatalytic processes for the degradation of pollutants could not be implemented on a practical scale till now, because of low reaction rates. To improve the rate of photocatalytic degradation processes, controlled periodic illumination (CPI) instead of continuous illumination was suggested. Sczechowski et al. (Chem.Eng.Sci., 1995, 50) attributed the improved conversions in Taylor vortex reactor, to CPI. To verify this phenomenon, experiments have been conducted in rotating annular flow reactor. The results of the reactor performance under continuous and controlled periodic illumination conditions will be discussed.