What is the anammox process and how is it applied in wastewater treatment?

Anammox (ANaerobic AMMonium OXidation) is a microbial process that converts ammonium and nitrite directly to nitrogen gas under anaerobic conditions. Reaction: NH4+ + NO2- -> N2 + 2H2O (deltaG = -357 kJ/mol). Organisms: Candidatus Brocadia, Kuenenia, Scalindua - slow-growing planctomycetes with doubling times of 10-14 days. Advantages over conventional nitrification-denitrification: 60% reduction in aeration energy (only partial nitritation needed), no external carbon source required (autotrophic), 90% less sludge production, reduced N2O emissions. Process configurations: SHARON-Anammox - two-stage partial nitritation followed by anammox. Single-stage systems (CANON, DEMON) - partial nitritation and anammox in one reactor. Mainstream applications - treating main wastewater flow with lower N concentrations. Sidestream applications - treating high-ammonia reject water from sludge dewatering. Challenges: slow organism growth requires long startup (months), sensitivity to inhibitors (oxygen, nitrite, sulfide), process control complexity. Over 100 full-scale installations worldwide.