A critical review of heterotrophic nitrification and aerobic denitrification process: Influencing factors and mechanisms

The heterotrophic nitrification and aerobic denitrification (HNAD) process can simultaneously remove nitrogen and chemical oxygen demand under completely aerobic conditions, which has more advantages than the conventional nitrogen removal process. This review summarized the history of the HNAD process, and the distribution of the microorganisms which can accomplish the HNAD process, and then, elucidated the effects of carbon source, C/N ratio, temperature, dissolved oxygen (shaking speed), heavy metals, salinity, and antibiotic on the performance of the HNAD bacteria. Moreover, the metabolic pathways and the mechanism of the HNAD process are discussed. At last, the problems and outlook relating to the study of the HNAD process were presented. In the HNAD process, the metabolisms of organic matter, heterotrophic nitrification, and aerobic denitrification are interlinked via the electron transportation systems which makes the HNAD process more complicated. Revealing the driven mechanism of the HNAD process is crucial for the application of the HNAD process in the future.