A sequencing batch reactor (SBR) was operated in this study to investigate the inhibitory kinetics of free ammonia (FA) on Nitrobacter. At the beginning of the experiment

FNA concentration in influent was changed to enrich Nitrobacter. Meanwhile

metagenomic species annotation and abundance analysis showed that Nitrobacter accounted for 40.3% of the total bacterial population. Then

the sludge enriched of Nitrobacter was used to study the variation rule of the specific oxygen uptake rate (SOUR) during nitrite oxidation process of batch tests. Furthermore

non-substrate inhibition model of FA inhibition on Nitrobacter activity was fitted. The results showed that the SOUR decreased with the increase of FA concentration as FA>7.3 mg·L-1. In particular

the SOUR was maintained at 0 g N·(g VSS·d)-1 when FA concentration was higher than 22.2 mg·L-1. Moreover

maximum specific oxygen uptake rate was 0.62 g N·(g VSS·d)-1. In addition

based on the degree of inhibition of Nitrobacter activity

the inhibition type of FA inhibition on Nitrobacter activity is in accordance with non-competitive reversible inhibition kinetics.