Direct contact membrane distillation (DCMD) process was applied for olive mill wastewater (OMW) treatment. Three commercial polytetrafluoroethylene (PTFE) membranes with different pore sizes (TF200 of 0.2 mu m, TF450 of 0.45 mu m and TF1000 of 1 mu m) were tested under different temperatures, namely, temperature difference and mean temperature. The aim of this study is to investigate the possibility of pure water production and concentration of natural polyphenols from OMW for further valorization. The results demonstrated the efficiency of DCMD process for OMW treatment by the three PTFE membranes. The permeate flux increased with the increase of the membrane pore size, the mean temperature and the temperature difference. However, no significant effect was detected between the pore size and the polyphenol separation coefficient, which remains close to 100% after 8 h of DCMD operating time. The DCMD processing of OMW using PTFE membranes allow to reach a concentration factor higher than 1.78 after 8 h of operating time, obtaining the best performance index for the membrane TF1000 with the greatest pore size. In addition, the effect of high temperatures on the phenolic content of OMW and its free radical-scavenging ability (DPPH assay) was also evaluated with time. It was found that a treatment of OMW by DCMD at high temperatures have no undesirable effects on the phenolic content and its antioxidant activity. (c) 2012 Elsevier B.V. All rights reserved.