Domestication of a cold-adapted ammonia-oxidizing functional flora and its bioaugmentation on A²/O wastewater treatment process at low temperature

In order to enhance nitrogen removal of sewage treatment processes in cold areas or seasons, a cold-adapted ammonia-oxidizing functional flora was obtained by domestication of activated sludge and used to augment the ammonia oxidation function in an anaerobic-anoxic-aerobic(A²/O)process operated at(14±1)°C. The seed sludge was collected from the secondary sedimentation tank of a local urban sewage treatment plant and domesticated in a sequencing batch reactor(SBR)for five operational cycles with selective medium at(14±1)°C. Loading with semi-soft fiber filler, the SBR was operated for another five operational cycles to immobilize the cold-adapted ammonia-oxidizing functional flora. The results showed that the ammonia oxidation capacity of the inoculated activated sludge was enhanced remarkably after domesticating for the five operational cycles with NH₃-N removal of 79.5% when the initial NH₃-N ranged from 205-236 mg·L^-1 in the SBR. After the next 5 operational cycles the cold-adapted ammonia-oxidizing functional flora was immobilized on the filler as biofilm. When the cold-adapted ammonia-oxidizing biofilm was put into the aerobic pool of the A²/O process with a mass ratio of 3.24%, the average ammonia removal in the process increased from 65% to 78%. The COD and total nitrogen removal was significantly improved as well. However, the ammonia removal in the low temperature A²/O process dropped slowly along with running time. Thus, the bioaugmentation effect in the long run should be investigated in the future.