In order to start up an autotrophic partial nitrification process

the coordinated control of the influent C/N loading rate was carried out in the lab-scale sequencing batch reactor (SBR) inoculated with heterogeneous granular biomass. During the operation period

the evolution of granule size distribution

extracellular polymeric substances (EPS) composition and dynamics activities of functional microbes were also investigated to elaborate main factors for the conversion of sludge characteristics. The results showed that the nitrite nitrogen (NO2--N) accumulation rate of SBR would reach around 1.34 kg·(m3·d)-1

with the persistent enhancement of ammonia-oxidizing bacteria (AOB) activity and the effective inhibition of nitrite-oxidizing bacteria (NOB)

represented by specific removal (μNO3-N) and NO2--N accumulation (μNO3-N) rates

respectively. Moreover

the mean diameter of sludge granular increased from 1.4 mm to around 2.2 mm with the color of reddish brown

while its settling ability was improved significantly. Benefited from the accumulation of EPS contents

AOB could be immobilized by granular sludge effectively

even if the settling time of reaction cycle was set at 3 min. In addition

the selective inhibition of NOB caused by both free ammonia (FA) and free nitrous acid (FNA) during the aeration period was the other main factor for stable partial nitrification.