Biofilm Community Dynamics in Bench-Scale Annular Reactors Simulating Arrestment of Chloraminated Drinking Water Nitrification

Annular reactors (ARs) were used to study biofilm community succession and provide ecological insight during nitrification arrestment through simultaneously increasing monochloramine (NH₂Cl) and chlorine to nitrogen mass ratios, resulting in four operational periods (I–IV). Analysis of 16S rRNA-encoding gene sequence reads (454-pyrosequencing) examined viable and total biofilm communities and found total samples were representative of the underlying viable community. Bacterial community structure showed dynamic changes corresponding with AR operational parameters. Period I (complete nitrification and no NH₂Cl residual) was dominated by <i>Bradyrhizobium</i> (total cumulative distribution: 38%), while environmental <i>Legionella</i>-like phylotypes peaked (19%) during Period II (complete nitrification and minimal NH₂Cl residual). <i>Nitrospira moscoviensis</i> (nitrite-oxidizing bacteria) was detected in early periods (2%) but decreased to <0.02% in later periods, corresponding to nitrite accumulation. <i>Methylobacterium</i> (19%) and members of <i>Nitrosomonadaceae</i> (42%) dominated Period III (complete ammonia and partial nitrite oxidation and low NH₂Cl residual). An increase in <i>Afipia</i> (haloacetic acid-degrading bacteria) relative abundance (<2% to 42%) occurred during Period IV (minimal nitrification and moderate to high NH₂Cl residual). Microbial community and operational data provided no evidence of taxa-time relationship, but rapid community transitions indicated that the system had experienced ecological regime shifts to alternative stable states