Anammox granular sludge was formed in an anoxic EGSB reactor

which was started up with the mixture of aerobic granular sludge and anammox biofilm. The reactor was operated under the regulation of key controlling factors

including substrate concentration and upflow velocity according to sludge properties and operating results. In this way

anammox granular sludge was formed faster. N removal efficiency

particle size distribution

granular surface morphology

internal structure and distribution of microorganisms were also determined. Mean granular size reached 0.556 mm after 80 d. NRR was 4.758 kg N·m-3·d-1 after 89 d. FISH analysis showed that anammox bacteria dominated the granular sludge. SEM and TEM showed that the granular sludge contained multiple gathered smaller granules with irregular shape and closely arranged internal structure.