Olive mill wastewater (OMW) is a major environmental problem in the Mediterranean basin. Although many methods for OMW treatment have been developed, only a few have been adopted in pilot-or full-scale applications. A full-scale system for aerobic biological treatment of OMW was developed. The system consists of a trickling filter and a recirculation tank. Continuous recirculation of the wastewater was used to provide oxygen concentrations from 0.7 to 1.2 mg L(-1). Low ambient temperatures did not affect system performance since the raw wastewater was warm enough. Nutrient addition was not necessary as raw wastewater contained sufficient nitrogen and phosphorous concentrations. Indigenous olive pulp bacteria proved to be resistant to full-scale conditions. Feed chemical oxygen demand and phenolic concentrations were about 43 000 and 9500 mg L(-1), respectively. The system reduced more than half of the organic load under continuous operation and a hydraulic retention time of 24 h. The efficiency of this method could be improved by combining it with another technology to further reduce the organic load. The absence of mechanical aeration and the very low hydraulic retention time denotes that the proposed system could be viable and attractive. (C) 2011 Society of Chemical Industry