A fluidized bed bioreactor (FBBR) was operated for more than 1000 days under two regimes, Methanogenic (M) and Methanogenic-Aerobic (M-A), to remove 2,4,6-trichlorophenol (TCP) and phenol (Phe) from a synthetic wastewater, containing different amounts of TCP and Phe, using different aeration flow-rates (0, 2.13, and 1.06 NL O-2/L.day). M conditions (80:20 mg/L of TCP:Phe, 0 NL O-2/L.day) showed similar TCP and Phe removal (> 95%). Nevertheless accumulation of 4-chlorophenol WIP) up to 16 mg/L and Phe up to 4 mg/L was observed, while in M-A conditions (80:20 mg/L of TCP:Phe, 2.13 NLO2/L.day)TCPand Phe removal achieved 99.9'% and after 70 days no accumulation of intermediates were detected. The increase of TCP and Phe in the influent under M-A conditions from 80:20 to 120:30 mg/L of TCP:Phe did not negatively affect the removal of TCIP, intermediates and Phe; in fact, they were similar to those in previous M-A conditions. The decrease in the oxygen flow rate from 2.13 to 1.06 NIL O-2/L.day had no negative effect on pollutant removals, which were as high as in previous two M-A conditions. The specific methanogenic activity of bioparticles of the fluidized bed decreased with long-term partial aeration, starting from 1.097 mmol CH4/ h.g(TKN) in the M regime (day 60) to < 0.02 mmoiCH(4)/h . gTKN at day 1050, suggesting aerobic regime in the bioreactor rather than an M-A regime. In conclusion, complete removal of TCIP and less chlorinated intermediates could be achieved in an initially methanogenic FBBR under conditions of partial aeration, although long-term operation seemed to negatively affect the methanogenic activity of biomass. It is also likely that after extended aeration the microbial community was finally enriched with strains with the ability to attack 2,4,6-TCP under aerobic conditions. This report represents the first evidence of a long exposure to oxygen of an anaerobic microbial consortium that efficiently remove TCIP. (c) 2006 Wiley Periodicals, Inc.