Review of salinity adaptation and application of functional microorganisms in biological ammonia removal from high-salinity wastewater

High-salinity, high-ammonia industrial wastewater faces treatment challenges, necessitating efficient, low-cost biological nitrogen removal. This review examines the distribution, salt tolerance, and potential of functional microbes in conventional and non-conventional ammonia oxidation under salinity. In conventional nitrification, ammonia-oxidizing bacteria (AOB, such as Nitrosomonas europaea ) dominate at low salinity (<3%) while nitrite-oxidizing bacteria (NOB, such as Nitrospira ) are inhibited, causing nitrite accumulation. At high salinity (>3%), halotolerant AOB (e.g., Nitrosomonas halophila ) drive partial nitrification (PN) with NOB severely suppressed. Among non-conventional approaches, ammonia-oxidizing archaea (AOA, such as Nitrosopumilus ) demonstrate strong salt tolerance at 1-3% salinity, often cooperating with AOB. Anaerobic ammonia oxidation (Anammox, such as Candidatus Scalindua ) coupled with PN, achieves 80–99% nitrogen removal in a salinity environment of 0.35%–3.5%. Complete ammonia oxidizers (Comammox, such as Nitrospira inopinata ) are inhibited by high salinity despite their simplified metabolism. Heterotrophic nitrification–aerobic denitrification (HN-AD) and heterotrophic ammonia assimilation (HAA) rely on salt-tolerant heterotrophs to achieve simultaneous nitrogen and carbon removal at salinities ranging from 2% to 11%. Current challenges include system collapse from salinity shocks, low functional microbe abundance, and reduced efficiency under extreme salinity (>5%). Future priorities can include developing extreme halotolerant microbes, designing intelligent multi-pathway reactors, and enhancing resource recovery.