BACKGROUND: This study evaluates the integration of ferric coagulation, Fenton oxidation (both at lab and industrial scale) and activated sludge (at lab scale) for the treatment of olive mill wastewater. RESULTS: Initially, an iron based coagulation at the raw pH of olive mill effluent was performed, leading to 38% COD abatement at bench scale. This procedure also provided some dissolved iron that can be used as catalyst in the following Fenton's peroxidation step. At lab scale Fenton's process accomplished COD removal of 75%. Moreover, some biodegradability enhancement was achieved with this procedure with initial BOD5/COD average = 0.03 increasing to BOD5/COD average = 0.37 after the process. This integrated treatment was then applied at industrial scale and, after further optimization, coagulation and Fenton's processes were able to remove 43% and 62% of COD, respectively. CONCLUSION: Based on the interesting results gathered at lab-scale, it was possible to optimize an industrial WWTP (wastewater treatment plant). Ferric coagulation followed by Fenton's peroxidation was implemented with efficiency up to 90% and final COD of 200 mgO(2) L-1. The resulting wastewater can be discharged into municipal sewage or can be recycled for reutilization after an in situ biological treatment. (C) 2016 Society of Chemical Industry