The treatment of waste metalworking fluids produces an aqueous phase which exhibits a high Chemical Oxygen Demand (COD) and which contains toxic components. In this work, the treatment plant includes ultrafiltration and nanofiltration membranes followed by a bioreactor and a microfiltration system. The product is a clear yellow aqueous phase containing residual levels of COD. Activated carbon is used in this work to eliminate residual dissolved organic compounds remaining after the treatment plant. Activated carbon treatment is tested at three different stages: after nanofiltration, to treat a nano-permeate; after the bioreactor, to treat biopermeate containing biological materials; and finally after microfiltration, to treat the bio-permeate without microorganisms. The efficiency of activated carbon after each stage is studied and the results are compared. The adsorption experiments were carried out in two modes. Firstly, a batch system was used to investigate the adsorption capacity of the adsorbent and fit model isotherms. Secondly, fixed continuous systems were set-up, and the feasibility of a real treatment of such effluents was assessed.