This project develops models with the objective of predicting the evolution of a system that treats paracetamol with the Fenton and photo-Fenton reactions. This objective is carried out by adjusting the parameters of a semi-empiric model, based on the model proposed by Orlando M. Alfano et. al. (2014). This project does not collect the experimental data. This project proposes a set of adjustments that predict the behavior of the system for different operational conditions. Each case uses a different set of experimental data in order to predict with more reliability, different aspects of the system. There are models with the objective of a general prediction of the system analyzing the behavior of paracetamol and hydrogen peroxide. Some of the adjustments make better predictions of the behavior of the reactants during the first minutes of the reaction, as a previous study of a system with dosage. Finally, some equations have been added to the model proposed by Orlando M. Alfano, in order to predict: the behavior of the intermediate products from the degradation of paracetamol and the evolution of TOC. These models, once adjusted, can predict, with acceptable reliability, the studied system within the range of validity without having to do new experiments.