Operation of a sequencing batch reactor for cultivating autotrophic nitrifying granules

The granulation of nitrifying sludge in a sequencing batch reactor (SBR) fed with NH4+-N-laden inorganic wastewater was investigated. After 120-day operation spherical and elliptical granules with an average diameter of 0.32 mm were observed. The hydrophobicity surface, settling velocity and specific gravity of the matured granules increased with the processing of sludge granulation. Spatial distribution of bacterial species within the autotrophic granules was analyzed with fluorescence in situ hybridization. Both ammonia- and nitrite-oxidizing bacteria were observed in the granular sludge. The Michaelis–Menten equation was used to describe their NH4+-N utilization rate, and the kinetic coefficients were calculated to be vm = 18.0 mg/g-VSS/h and Km = 36.7 mg/l. Taking into account the NH4+-N utilization rate and removal efficiency together, an NH4+-N concentration range of 100–250 mg/l was found to be favourable for the operation of the SBR to cultivate nitrifying granules.