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

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.