The Heterotrophic Nitrification and Aerobic Denitrification (HN–AD) Process

Abstract

Autotrophic nitrification and heterotrophic denitrification processes are considered as conventional biological nitrogen removal methods. A single reactor system for these processes is highly complex and difficult, due to the difference in: (i) DO requirement and tolerance, (ii) microorganisms and their metabolism, (iii) reactor configurations and loading rates, and (iv) factors responsible for effective removal. Recent decades have observed the development of efficient single-stage nitrogen removal processes, such as Anammox and its modifications, Comammox, Dissimilatory Nitrate Reduction to Ammonia (DNRA) and HN–AD. Among these processes, HN–AD offers several advantages as the metabolically versatile bacteria can accomplish one-stage nitrogen removal in aerobic conditions in the presence of organic carbon. Hence, this chapter, comprehensively reviews the HN–AD process to create better understanding and applicability. This chapter talks about the diversity and distribution of HN–AD microbes, the nutrient removal mechanism (N, C and P), factors affecting the performance of the HN–AD process and the application of HN–AD in wastewater treatment facilities with perspectives on the future scope of research.