Heterotrophic nitrifying bacteria in wastewater biological nitrogen removal systems: A review

With the ability to use organic compounds, to rapidly proliferate, and to achieve simultaneous nitrification and denitrification, heterotrophic nitrifying bacteria (HNB) have remarkable potential in wastewater biological nitrogen removal (BNR) engineering fields. This review provides a comprehensive and systematic overview of the current knowledge of HNB in wastewater BNR systems. First, it briefly summarizes the general nitrogen transformation pathway and the physiological-biochemical features of HNB. Subsequently, it highlights the phylogenetic diversity of HNB isolates from wastewater BNR systems and their bioaugmentation applications in wastewater BNR systems. Recent developments in the detection of HNB gene abundance and heterotrophic nitrifying activity in wastewater BNR systems is also discussed extensively. This will improve our fundamental understanding of the contribution of HNB to ammonia oxidization in wastewater BNR systems in the presence of various autotrophic ammonia-oxidizing microorganisms, which is important for the control, improvement, and optimization of wastewater BNR systems.