Kinetics, diffusional limitation and microscale distribution of chemistry and organisms in a CANON reactor

In the Completely Autotrophic Nitrogen removal Over Nitrite (CANON) process, aerobic and anaerobic ammonia oxidizing bacteria cooperate to remove ammonia in one oxygen-limited reactor. Kinetic studies, microsensor analysis, and fluorescence in situ hybridization on CANON biomass showed a partial differentiation of processes and organisms within and among aggregates. Under normal oxygen-limited conditions (∼5 μM O2), aerobic ammonia oxidation (nitrification) was restricted to an outer shell (<100 μm) while anaerobic ammonia oxidation (anammox) was found in the central anoxic parts. Larger type aggregates (>500 μm) accounted for 68% of the anammox potential whereas 65% of the nitrification potential was found in the smaller aggregates (<500 μm). Analysis with O2andNO2- microsensors showed that the thickness of the activity zones varied as a function of bulk O2andNO2- concentrations and flow rate.