厌氧氨氧化菌(anaerobic ammonium oxidation, Anammox)是一类细菌，属于浮霉菌门，包括(Candidatus Brocadia)、(Candidatus Kuenenia)和, Candidatus "Anammoxoglobus", Candidatus "Jettenia", (Candidatus Scalindua)属。它们至今未能成功分离得到纯菌株，因此尚未获得正式命名和分类。它们可以在缺氧环境中，将铵离子(NH₄)用亚硝酸根(NO₂)氧化为氮气：

NH₄ + NO₂ → N₂ + 2 H₂O, ΔG = -357 kJ mol

Anammox, an abbreviation for ANaerobic AMMonium OXidation, is a globally important microbial process of the nitrogen cycle. The bacteria mediating this process were identified in 1999, and at the time were a great surprise for the scientific community. It takes place in many natural environments and anammox is also the trademarked name for the anammox-based ammonium removal technology that was developed by the Delft University of Technology.