During the last century there has been a growing concern about water pollution throughout the developed countries. Water has a major impact on the environment as it is used by all living being. This leads to leave the wastewater used with an acceptable quality for its next destination. Fortunately, national and international water quality agreements and laws have pushed development of wastewater treatment technology that nowadays allows us to return the used water to the environment in good conditions. Nevertheless, more modern and simpler technologies should be researched in order to make wastewater treatment a process reachable all around the world within the minimum environmental impact and minimizing waste. This thesis researches one of the technologies with more future in this field; the Fenton process, a reaction that belongs to the Advanced Oxidation Processes (AOPs). The aim of this thesis is to optimise the Fenton reaction. This has been done by testing different catalysts, concentration of chemicals, and operational conditions. In this context, the experiments performed in the frame of this study have explored: - The feasibility of the iron/iron oxide catalyst. - The optimum reactive conditions for the heterogeneous Fenton process; the reaction pH, concentration of the H2O2 and temperature. - The optimal preparation of the catalyst in terms of its level of oxidation and Its potentials or limitations in applied Fenton process. Towards the checking of these parameters the experiments were conducted using propionic acid (PA) as a model of organic substance with nine different iron oxide catalysts in order to simulate a wastewater sample under the Fenton’s reaction and with a regular checking of the amount of total organic carbon (TOC) with time. Obtained results showed good process efficiency near to 50% of TOC removal, working at a smoothly acid pH and without remarkable iron leaching at 60 ºC and an excess of H2O2.