Advanced Oxidative Process (POA) are among the most important new technologies to treat effluents, mainly those which present high toxicity that does not allow for the use of biological processes. This works presents a new methodology for the optimization of photochemical reactors which can make it possible to improve the applicability advanced oxidative processes. The procedure is based on the estimation of the empirical reaction rate which requires an efficient fitting of mathematical models to experimental data under different operational conditions. The Curve fitting Modified Spline Method was used to fit the experimental data.