The treatment of actual olive mill wastewaters, coming from an evaporation pond subjected to climatic conditions, was studied by the heterogeneous Fenton process with the laboratory catalyst Fe-Ce-O 70/30. Investigating the impact of the solid load, hydrogen peroxide concentration, and pH over the methodology efficiency a full factorial experimental design was followed by results stating that the amount of Fe-Ce-O 70/30 and pH had a high influence on final depuration, while [H2O2] was not statistically relevant. Reduced models based on those data showed some ability to predict chemical oxygen demand (COD) removal, final effluent biodegradability, and iron leached concentration. Also respirometric and luminescence techniques were used to evaluate toxicity. The recommend operational conditions gathered up when each one of the response factors was optimized were diverse. From those, it seemed appropriate to run with high Fe-Ce-O loads (1.5 g/L) allied with pH = 4 and [H2O2]= 115 mM since, even if COD degradation (24%) was not the highest one, the final effluent was very biodegradable (BOD5/COD = 0.54) allowing the application of an activated sludge post-treatment. Furthermore, for these conditions, catalyst stability was safeguarded since Fe elution was low (0.12 mg/L). Finally, the catalytic system involving Fenton's peroxidation Fe-Ce-O 70/30 was revealed to be promising for real olive mill wastewaters biodegradability improvement and toxicity removal enabling a proper postbioremediation.