Heterotrophic nitrification, anaerobic ammonia oxidation and archaeal ammonia oxidation in a new nitrogen cycle

The global nitrogen cycle is driven by a series of microbial activities. In the past few years, the understanding of nitrogen cycling processes has changed dramatically based on some new processes, including heterotrophic nitrification, anaerobic ammonium oxidation ( Anammox) and archaeal ammonia oxidation. In this review, the discovery, biochemistry mechanism and molecular biology of organisms linked to these processes are presented and relevant unknown questions are highlighted. A new nitrogen cycle will only emerge through considering all of these processes and microbial groups together. In addition, the paper presents some new perspectives about the application of these new organisms in biological nitrogen removal from wastewater. These new perspectives include enriching heterotrophic nitrification bacteria to enhance simultaneous nitrification-denitrification, enriching Anammox to achieve single-stage autotrophic nitrogen removal and enriching ammonia oxidation archaea to improve nitrogen removal efficiency at low dissolved oxygen (DO)