- Laboratory reactor systems based on the conventional (aerobic) activated sludge process and on the contact (anaerobic) process were operated almost one year in order to develop a biological process for the degradation of the fire retardant tetrabromobisphenol A (TBBPA) and to find out if its degradation might result in the formation of the endocrine disruptor bisphenol A (BPA). The reactors were fed a TBBPA waste mixture containing also tribromophenol (TBP), and added with contaminated sediments that might have contained indigenous bacteria exposed to these compounds. Various organic compounds were used as potential electron donors to enhance growth of halorespiring bacteria that would debrominate the TBBPA and make it available for further aerobic mineralization. In spite of the various operating strategies applied and the different carbon sources added, no TBBPA biodegradation has been observed and no accumulation of intermediates such as BPA in any of the aerobic or anaerobic reactors has been detected. TBP on the other hand, was found to be easily biodegraded by aerobic cultures simulating the activated sludge process. This was linked to consistent accumulation of bromides, released to the liquid following TBP breakdown.