The olive oil mill wastewater (OMW) sample tested was collected in an evaporation pond immediately after the annual olive oil production and was the by-product of a three-phase olive oil extraction process. OMW was stored in screw-caped glass flasks, at 4 °C, until the start of the experiments. Before use OMW was grossly filtered with a filter paper to remove the coarse particles under suspension and previously 50% diluted with distilled water. No further dilutions were made for the chemical or biological treatments. The major characteristics of the diluted effluent were