Formation and characteristics of nitrifying biofilm on a membrane modified with positively-charged polymer chains

Nitrifying bacteria hardly adhered to the surface of supporting materials in a fluidized bed bioreactor containing only inorganic compounds. The adhesivity of nitrifying bacteria was compared, between an unmodified membrane and a membrane modified with diethylamino groups, using the grafting method. The result showed that the diethylamino-group-grafted membrane successfully increased the adhesivity of nitrifying bacteria, which might be due to particular properties of the grafted membrane surface, such as positive charge and soft polymer chains. Moreover, the thickness of the biofilm exceeded 100 mu m after incubation for 150 days in a continuously fed fluidized bed bioreactor. The results of fluorescence in situ hybridization (FISH) confirmed that the biofilm consisted mostly of ammonia-oxidizing bacteria. Moreover, the biofilm exhibited a much higher nitrification rate per unit area than other biofilms, which was confirmed by the analysis of the concentration profile of ammonium-nitrogen inside the biofilm using a microelectrode that we originally fabricated. (C) 2000 Elsevier Science B.V. All rights reserved.