In situ probing of microbial activity within anammox granular biomass with microelectrodes

• Beside biofilm, granules with average diameter of approximately 5 mm formed in an AnRBC.
• In situ microbial activity of anammox and denitrification within granules were investigated with microelectrodes.
• The most active zone of anammox was in the surface layer of 200–400 μm, and anammox activity increased with increasing of substrate concentration.
• Denitrification activity was identified and the most active zone was limited to the inner layer of the granules.

An anaerobic rotating biological contactor was fed with inorganic synthetic wastewater for anammox. Besides biofilm, granular biomass with average diameter of approximately 5 mm formed. NH4+, NO2−, NO3− and pH microelectrodes were used to probe microbial activity in situ within the granules. At a sufficient substrate concentration, the anammox reaction was observed in the upper layer of granules, and the most active zone was found to be in the surface of 200–400 μm. The in situ anammox activity increased with increasing substrate concentration, and a maximum ammonium consumption rate of 83.3 μmol cm−3 h−1 was obtained at an ammonium concentration of 1000 μmol L−1. Under an ammonium-limited condition, denitrification activity was observed in the inner layer, and the most active zone was limited to 700–1000 μm. This study revealed that denitrification bacteria coexisted with anammox bacteria within inorganic anammox granules.