Oxygen-limited nitrification and denitrification in a lab-scale rotating biological contactor

Rotating Biological Contactors (RBC) treating highly nitrogenous wastewaters are known to give rise to nitrogen losses, generally assumed to be due to concomitant nitrification and denitrification. In this study, a lab-scale nitrifying RBC reactor was shown to bring about losses of nitrogen of the order of 10 to 20% at ammonium loading rates of up to 2129 mg N m(-2) d(-1), when no extra carbon source was added. These higher removal values could be due to Oxygen-Limited Autotrophic Nitrification and Denitrification (OLAND), because the reactor was operated at oxygen limitation. When methanol was added as a soluble organic carbon source to further diminish oxygen transfer into the deeper parts of the biofilm, the RBC achieved 84% nitrogen removal (loading rate 2300 mg N m(-2) d(-1)) at a COD/N ratio of 3.1. The latter also suggests that the process was occurring parallel to conventional denitrification.