The fish canning industry generates large volumes of wastewater for which the treatment is particularly difficult due to the high content of organic matter and salts and to the significant amount of oil and grease they present.In this work, a closed jacketed batch reactor was used to study the feasibility of applying a Fenton reaction step after an activated sludge biological treatment. For this purpose and in order to find optimal conditions, a 33 Box-Behnken full factorial design was used. The predicted optimum value (63% DOC degradation) was found for hydrogen peroxide concentration of 1558 mg/L, iron concentration of 363 mg/L and pH 3.2