Understanding the effect of free ammonia on microbial nitrification mechanisms in suspended activated sludge bioreactors.

Abstract During nitrification, the varieties of microbial structures, metabolic pathways and functional profiles in four parallel laboratory-scale sequencing batch reactors (SBRs) with 0.5, 5, 10 and 15 mg/L of free ammonia (FA) concentrations were analyzed by high-throughput sequencing of the 16S rRNA gene. The SBRs were named S0.5, S5, S10 and S15, respectively. Ammonia removal via the nitrate pathway was achieved in S0.5 and S5 throughout the whole experimental period, while ammonia removal via the nitrite pathway was established in S10 and S15 after 89 and 146 day, respectively. The key finding of this study is that both the microbial diversity and richness were significantly affected (p