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Denitrification and anammox remove nitrogen in denitrifying bioreactors

Rambags, Femke, Tanner, Chris C., Schipper, Louis A.
Ecological engineering 2019 v.138 pp. 38-45
ammonium, anaerobic ammonium oxidation, bioreactors, carbon, coir, denitrification, gravel, monitoring, municipal wastewater, nitrates, nitrogen, stable isotopes, wastewater treatment, wood chips
Denitrification has been considered the main pathway converting nitrate (NO3–) to dinitrogen gas (N2) in denitrifying bioreactors. Here, the importance of an alternative nitrogen (N) removal process, namely anaerobic ammonium oxidation (anammox), was assessed by monitoring the removal of N species from partially nitrified municipal wastewater passing through fifteen mesocosm scale (∼700 L) bioreactors containing woodchip, coconut husk or gravel during their initial and eighth year of operation. Additionally, lab experiments using a 15N isotope-pairing technique were performed to partition production of N2 to these different microbial processes. The effective removal of both NO3– and ammonium (NH4+) and the formation of hybrid N2 (i.e. 29N2) observed in this study demonstrated that, along with denitrification, anammox was an effective pathway for N removal when both NO3– and NH4+ were present. Anammox removal rates ranged from 0.6 to 3.8 g N per m3 per day, while denitrification rates ranged from 0.7 to 2.6 g N per m3 per day. The contributions of anammox to N removal was dependent on media, with anammox becoming more dominant in bioreactors where denitrification was carbon limited. Designing denitrifying bioreactors to support both denitrification and anammox expands the utility of these passive approaches for improving treatment of wastewater.