Two laboratory scale biofilm bioreactors of identical configuration were set up and tested for the continuous treatment of waters artificially contaminated with simple or complex mixtures of low chlorinated biphenyls (PCBs) and chlorobenzoic acids (CBAs). Frosted glass beads and polyurethane foam cubes were employed as immobilization supports. A three-membered aerobic bacterial co-culture, that was previously shown to have a high degradation and dechlorination activity towards PCBs in fixed bed batch bioreactors, was used to inoculate both biofilm reactors. The two bioreactors developed, operating in a continuous mode, were both capable of degrading and stoichiometrically dechlorinating the PCBs and CBAs present in the influent. The PCB degradation and dechlorination efficiency of the reactors did not decrease by increasing the organic load or by changing the influent composition, thus indicating a good stability and versatility of the developed process. (c) 2005 Elsevier Ltd. All rights reserved.