Olive oil mill wastewater (OMW) is a concentrated effluent with a high organic load. It has high levels of organic chemical oxygen demand (COD) and phenolic compounds. This study presents a unique process to treat OMW. The process uses ultrafiltration (UF) membranes modified by a functionalized multi wall carbon nano-tube (F-MWCNT). The modified tube has an inner diameter of 15-30 nm and is added to the OMW treatment process to improve performance of the membrane. Tests were done to evaluate the following operating parameters of the UF system; pressure, pH and temperature; also evaluated parameters of permeate flux, flux decline, COD removal and total phenol rejection. The Taguchi robust design method was applied for an optimization evaluation of the experiments. Variance (ANOVA) analysis was used to determine the most significant parameters affecting permeate flux, flux decline, COD removal and total phenols rejection. Results demonstrated coagulation and pH as the most important factors affecting permeate flux of the UF. Moreover, pH and F-MWCNT UF had significant positive effects on flux decline, COD removal and total phenols rejection. Based on the optimum conditions determined by the Taguchi method, evaluations for permeate flux tests; flux decline, COD removal and total phenols rejection were about 21.2 (kg/m(2) h), 12.6%, 72.6% and 89.5%, respectively. These results were in good agreement with those predicted by the Taguchi method (i.e.; 22.8 (kg/m(2) h), 11.9%, 75.8 and 94.7%, respectively). Mechanical performance of the membrane and its application for high organic wastewater treatment were determined as strong.