The aerobic biodegradation of methyl tert-butyl ether (MTBE) was investigated using a pilot-scale Biomass Concentrator Reactor (BCR). The reactor was operated for a year at a flow rate of 2500 L/d of Cincinnati dechlorinated tap water and an influent MTBE concentration of 5 mg/L. At steady state conditions, the total removal efficiency of MTBE in the reactor exceeded 99.9 %. Effluent concentrations of MTBE and its degradation byproduct tert-butyl alcohol (TBA) reached levels below 1 ug/L, with the latter consistently present at lower concentrations. In addition, the effluent was found to be of better quality than the GAC-treated tap water fed into the reactor as measured by dissolved organic carbon. Includes 20 references, table, figures.