A photo impinging streams reactor was employed to study the degradation of phenol in aqueous solutions applying titanium dioxide nanopartides as the reaction catalyst. The central composite experimental design method was applied to determine the pertinent operating parameters of such a process. These were phenol concentration, catalyst loading, pH of the slurry, and the feed flow rate. Residence time distribution (RTD) of the slurry phase within the reactor was measured using the impulse tracer method. A compartment model consisting of a number of mixed and plug flow regions was assigned to describe the flow pattern in the reactor. On the basis of such an arrangement and applying the Markov chains discrete time formulation, a three parameters model was derived for the RTD. The parameters of the theoretical RTD model were evaluated by comparing the latter with those determined experimentally. The RTD expression was applied in conjunction with the phenol degradation kinetic model to predict the apparent rate coefficient for such a reaction. The higher values observed for the apparent rate coefficient in impinging streams reactor than those available in the literature may be explained by the mass transfer limitations affecting the conventional reactors performance.