Abstract:Under extreme water quality conditions such as high salt, high or low temperatures, high ammonia nitrogen, and heavy metals, conventional biological denitrification suffer from reduced biological activity, slowed reaction, and unsatisfactory outcomes. Therefore, the development of efficient functional bacteria capable of withstanding extreme water quality environments is crucial for enhancing the stability of biological denitrification processes. Heterotrophic nitrifying-aerobic denitrifying bacteria can remove nitrogen under completely aerobic conditions. Some of these bacteria can grow under extreme water conditions and demonstrate efficient nitrogen removal capability, offering suitable strain resources for conventional biological nitrogen removal. A variety of heterotrophic nitrifying-aerobic denitrifying bacteria such as Pseudomonas and Acinetobacter capable of tolerating extreme water quality conditions have been screened out. Under extreme water quality conditions, heterotrophic nitrifying-aerobic denitrifying bacteria increase the activities of the enzymes involved in the denitrification pathway to maintain the stability of their denitrification performance. Moreover, they increase the activities of the antioxidant enzymes to adapt to the extreme water environments. We summarize the species, denitrification efficiency, metabolic pathways, and mechanisms of heterotrophic nitrifying-aerobic denitrifying bacteria in extreme water environments characterized by high concentrations of ammonia nitrogen, elevated salinity, extreme high or low temperatures, heavy metal contamination, and extreme pH. Additionally, this paper assesses the current application status of these bacteria in engineering, identifies the technical challenges, and proposes novel research ideas for future investigations.
