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Abstract
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Granulation of nitrifying bacteria was investigated in a continuous bubble column bioreactor.Then,the combined
effect of aeration and ammonium loading rates on dissolved oxygen(DO) concentration as well as nitrification process
was evaluated in the system using an experimental design technique. After 120 days,stable nitrifying granules with
average diameter of 1.4 mm and settling velocities of 55 m/h were obtained. The influence of increasing ammonium
loading rate(ALR)was found to be more significant than decreasing aeration rate on the reduction of DO concentration
inside the nitrifying bioreactor. The system could handle the ALR values of 0.48–1.92 gNH4 +-N/L d with the ammonium
removal efficiency from 65% to nearly 100% at the tested airflow rates of 2.5 and 4.5 L/min. At the low aeration, the
complete ammonium conversion to nitrate was replaced with nitrite when the ALR increased to 1.44gNH4
+-N/L d.
At the high aeration, however, almost complete nitrification was achieved except the high ALR in which the nitrite
accumulation was observed up to 38%.The study demonstrated that the continuous bioreactor had a considerable
performance for obtaining stable nitrifying granules to have nitrite accumulation under control with changing the
ratio of aeration rate and ALR.
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