Achieving transformation from denitrifying biofilter to partial denitrification/anammox biofilter through self-enrichment of anammox bacteria

Abstract

The application of anammox in denitrifying biofilter (DNBF) has been proven to be stable and feasible, but self-enrichment of anammox bacteria (AnAOB) in DNBF is difficult and rarely reported. During a 111-day operation in a single-stage DNBF, average NH4+-N removal remained at only 0.55 mg/L, showing limited partial denitrification/anammox performance. Subsequently, in another two-stage DNBF system, an average NH4+-N removal of 6.45 mg/L was achieved in 164 days, better than single-stage DNBF. Batch tests revealed partial denitrification activity of the primary biofilter and anammox activity of the secondary biofilter. Metagenomic analysis demonstrated that the secondary biofilter enriched Candidatus Brocadia from 0 to 23.81 %, 11.16 % and 14.09 % in the top, middle and bottom sections, respectively. Key enzymes of AnAOB including hdh and hzs, were distributed along the secondary biofilter, confirming the main role of anammox in nitrogen removal. Overall, this study demonstrated the potential for transformation from conventional denitrifying biofilter to partial denitrification/ anammox biofilter through self-enrichment of AnAOB in two-stage DNBF system compared to the single-stage DNBF.