Performance of Marine Anammox Candidatus Scalindua sp. under High Nitrate Conditions in a Biofilm Reactor

Abstract

To investigate the NO₃^– tolerance of Candidatus Scalindua sp., a continuous reactor was gradually exposed to increasing NO₃^– concentrations up to 3,200 mg N L^–1. High NH₄⁺ and NO₂^– removal efficiencies were maintained up to 2,600 mg N L^–1, above which performance declined and Ca. Scalindua relative abundance decreased to 0.8%. After one year of recovery, removal efficiencies exceeded 97%, whereas Ca. Scalindua relative abundance only reached 6.5%. EC₅₀ values for NH₄⁺ and NO₂^– were both 3,000 mg N L^–1. We demonstrated that our enriched Ca. Scalindua population tolerated NO₃^– up to 2,600 mg N L^–1, far exceeding the levels typically encountered in most human-derived wastewaters.