Coupling anammox with heterotrophic denitrification for enhanced nitrogen removal: A review

Anammox has been recognized as the current most cost-effective nitrogen removal process. However, the issue of excess nitrate residue from its effluent remains to be addressed in order to meet the increasingly stringent discharge standard. Other than nitrogen, certain types of wastewater have organic matter that also needs to be removed. Within this context, denitrification can be introduced to reduce nitrate produced in anammox process and improve effluent quality. Meanwhile, the organic content of wastewater can be also controlled. In such integrated system, maintaining the predominant role of anammox is of supreme importance in achieving the stable operation. This study reviews the strategies to establish a competition balance between anammox and denitrification processes by analyzing the kinetics of anammox and denitrifying microorganisms, discussing the favorable conditions in establishing the coupled process, and evaluating the system recovery approaches. Moreover, the dynamics of the microbial communities in response to the organic matters are also presented in order to better understand the complex interactions inside the system and provide a molecular insight in regulating the growth of the two functional bacteria for the stable coexistence. This review offers a guide for future engineering application on anammox coupled denitrification technology for advanced nitrogen removal.