Granulation of simultaneous partial nitrification and anammox biomass in one single SBR system

The granulation of simultaneous partial nitrification and anaerobic ammonium oxidation (Anammox) was investigated in a single, oxygen-limited, sequencing batch reactor. In this research, the reactor was started anaerobically and fed using the synthetic medium described by Van de Graaf et al. to cultivate Anammox biomass after inoculation with methanogenic granular sludge. Subsequently, mixture gas (air and nitrogen gas) was supplied to the reactor and a nitrifying population developed. Research results indicated that autotrophic granules was cultivated successfully by controlling the dissolved oxygen in the reactor between 0.3 and 0.5 mg/L, and a total inorganic nitrogen removal efficiency of 63.7% was obtained with a higher nitrogen load increased by reducing HRT to 3 days. It was also seen that the Ca and P concentrations of the feeding medium are important factors that influence the autotrophic granules from process running. When the Ca and P concentrations were exceeded the necessary quantity, salt precipitation was observed, interfered with microbial activity, and caused a decrease of the nitrogen removal rate of the system. After diminishing adequately the Ca and P concentrations, salt precipitation was avoided and the activity of the system restored quickly. Moreover, visual indication and scanning election microscopy observation revealed the process of sludge evolution and inner structure of the granules.