A porous gas permeable membrane can supply oxygen effectively, utilizing the high ability of oxygen uptake of nitrifying biofilm. If the membrane with the biofilm is applied to wastewater treatment, simultaneous denitrification occurs, but control of the biofilm thickness is necessary to maintain the high efficiency of the treatment.

In this research, small fluidized cylinders were tested as the media for slough off of excess biofilm, and the performance of nitrogen removal was investigated supplied with municipal wastewater. The results showed that the nitrogen removal efficiency was well kept for a long period with the method tested, especially the nitrification rate in the range of 1.1 to 3.1 gN/(m2 d), and that the biofilm formed a stable structure of double layers, that is, an inner firm nitrifying biofilm and an outer loose denitrifying biofilm.

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