Biodegradation of chloroorganic compounds in real industrial bleaching effluents (chlorination and extraction), with adapted biofilm in fluidized sand bed reactors, was studied under aerobic and anaerobic conditions. The effluents were only diluted and supplied with mineral nutrients. Two reactor combinations were compared with a single stage aerobic digestor (AFB). In the anaerobic-aerobic reactors in series (AAS), the effluents were first treated anaerobically followed by an aerobic reactor in a single pass. In the anaerobic-aerobic recycle reactor (AAR), the reactor content was periodically moving back from aerobic to anaerobic fluidized beds. The reactors were running continuously for one year. The most significant differences observed were between aerobic and anaerobic single reactors. Generally anaerobiosis reduced performance in terms of global parameters (COD, NPOC, AOX). With a residence time of 18 h for each reactor, COD and AOX typically decreased by 15-32 % for each aerobic reactor system (AFB, AAS, AAR), whereas a decrease of typically 4-15 % was observed in the purely anaerobic system. From GC and GC/MS analysis it was evident that in the anaerobic reactors, 2,4,6-trichlorophenol was first converted to 2,4-dichlorophenol. In all three systems 2,4,6-trichlorophenol and dichlorophenols were almost completely removed.