1999 Volume 22 Issue 3 Pages 206-214
Ammonium oxidation in wastewater biofilms grown on rotating biological contactors (RBCs) was investigated by using microelectrodes and fluorescent in situ hybridization (FISH) technique. The density of ammonia-oxidizers which formed dense cell cluster was about 5 times higher in the innermost biofilm than in the middle and surface of the biofilm. Due to the presence of ammonia-oxidizers throughout the biofilm, ammonium oxidation zone was expanded with increasing in oxygen penetration depth, which consequently resulted in an increase of the overall ammonium flux into the biofilm. Specific ammonium oxidation rate was dependent upon the density of ammonia-oxidizers. Although more ammonia-oxidizers were detected in the innermost layer, they might be in the dormant state and not contribute ammonium oxidation during the RBC operation because of substrate transport limitation. Furthermore, the fraction of O2 consumption for nitrification to total O2 consumption was in the range of 35% -53% in a medium with ammonium as the sole electron donor, indicating the biofilm consumed a significant amount of oxygen for other than nitrification. It implied that heterotrophs would grow and outcompete nitrifiers in biofilms even though there was no organic carbon source in the medium. In conclusion, the combination of microelectrode measurements and FISH technique made it possible to relate the spatial organization of ammonia-oxidizers with their in situ ammonium oxidation rates in biofilms, which obviously providing more insight into the nitrification process in wastewater biofilm systems.