Impact of long-term partial aeration on the removal of 2,4,6-trichlorophenol in an initially methanogenic fluidized bed bioreactor

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 O2/L·day). M conditions (80:20 mg/L of TCP:Phe, 0 NL O2/L·day) showed similar TCP and Phe removal (>95%). Nevertheless accumulation of 4‐chlorophenol (4CP) 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 NL O2/L·day) TCP and 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 TCP, 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 NL O2/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·gTKN in the M regime (day 60) to