Various anthropogenic activities and extensive urbanization are responsible for the generation of large amounts of wastewater containing toxic pollutants. Ammonia is one of the major pollutants in wastewater produced from households, industry and agriculture fields. Removal of ammonia during wastewater treatment is still a challenge. The conventional methods include two-step processes such as nitrification and denitrification. However, newly discovered processes of anammox and comammox seem to be more promising. This review elucidates on sources of ammonia contamination and its effects. Newly discovered process like anammox and comammox is discussed in detail. The habitat, abundance, the structure of bacteria and the chemical reactions involved in the processes are included in this review. Authors have brought out the analogy of the anammox process with the conventional nitrogen cycle and by coupling anammox with comammox to develop an efficient ammonia removal process. © 2021 Elsevier Ltd