Biosurfactants improve the removal of some recalcitrant pollutants in contaminated water and soil. The production and usage of man-made chemicals in industry has led to the entry of any xenobiotics into the environment. One such group of xenobiotics is chlorinated phenols. In this study, the treatment performance of 4-chlorophenol (4-CP), which is one of the most recalcitrant chlorophenols, was investigated using a biosurfactant added activated sludge bioreactor system with changing sludge retention time. Glucose was used as co-substrate and the COD concentration was kept constant during the experiments. JBR 425 rhamnolipid was used as biosurfactant. A control reactor (without biosurfactant; R1) and a test reactors (with biosurfactant addition; R2 and R3) were used in parallel tests. Three lab-scale continuous reactors were run in parallel with the same chemical oxygen demand (COD) and 4-CP loading rates. COD, 4-CP removal efficiencies and biomass concentrations with varying sludge age (3-25 days) were investigated. The effects of food to mass (F/M) ratio on the COD and 4-CP removal efficiencies were also investigated in the reactors. Operation at a sludge age of 3 days resulted in more than 77% COD and 46% 4-CP and 81% COD and 63% 4-CP removals in R2 and R3, while it resulted 61% COD and 19.15% 4-CP removals in R1.