Di-(2-ethylhexyl) phthalate (DEHP) is one of the most representative persistent micro-pollutants detected in the sewage sludge. In the present study, the presence of DEHP and its removal in various treatment units of a sewage treatment plant (STP) including an attached growth biological system i.e., a rotating biological contactor (RBC) and a suspended growth biological system i.e., activated sludge process (ASP) were investigated. Representative samples of sewage and sludge were collected at each stage of the STP for 2 years to explore the DEHP flow in the dissolved (DEHPd) and adsorbed (DEHPa) phases. The combination of RBC with a final clarifier was responsible for 50.4 and 58.2% of DEHPd and DEHPa removals, respectively. Both DEHPd and DEHPa removals were greater in RBC compared to ASP, demonstrating that an attached growth biological system is more efficient in the removal of DEHP compared to the suspended growth biological system. A good correlation between DEHP and organic matter removal was observed by using Pearson-correlation matrix approach.