Metagenomic insights into the explanation of biofilter performance distinction induced by dissolved oxygen increment

Abstract In this study, a set of novel double-layer-packed sequencing batch biofilm reactors (SBBRs) were constructed to treat secondary effluent with a low carbon-to-nitrogen ratio (C/N = 3.0). All the reactors were operated under identical conditions except dissolved oxygen (DO) in the aerobic section, which was controlled at seven different levels (0.5, 1.0, 1.5, 2.0, 2.5, 3.5 and 4.5 mg/L). It was found that the aerobic section contributed most to performance at an optimal DO of 2.0 mg/L. The change in DO accounted for the varied bacterial communities, which resulted in different performances. Both bacterial community structure and potential functions displayed close associations with performance implying nutrients were mainly removed by simultaneous nitrification-endogenous denitrification and phosphorus removal (SNEDPR) process. Moreover, the proliferation of nonfunctional nitrifiers/denitrifiers led to the inhibition of denitrification resulting in a lower removal of total dissolved nitrogen and phosphorus.