Chapter 4: State-of-the-Art Anaerobic Ammonium Oxidation (Anammox) Technology

The nitrogen (N) cycle, one of the most important biospheres on Earth, consists of complex interactions among various nitrogen compounds. Anaerobic ammonium oxidation (Anammox) is a N-transformation pathway that was discovered in the 1990s. The metabolism of Anammox bacteria relies on the oxidation of ammonium for energy using nitrite as the electron acceptor to form nitrogen gas. Due to its chemolithoautotrophic nature, lack of requirement for aeration and organic carbon (C), as well as the high efficiency of N-compounds' conversion to nitrogen gas, Anammox holds an attractive potential for N-removal from wastewaters, especially for those with a low “carbon/nitrogen (C/N)” ratio. This chapter presents the up-to-date information of Anammox bacteria genera and their versatile metabolic pathways found by a number of advanced molecular techniques, and also gives a brief summary on their potential nitrogen sources of cell synthesis through microbial thermodynamic calculations. Considering its applicability for nitrogen removal from wastewaters (both for high-strength and dilute strength), the effect of solid retention time on the nitrogen removal efficiency and inhibitors on Anammox process are discussed. Moreover, its possible involvement in syntrophy for sulfate reduction and ammonium oxidation triggers scientists to wonder if it plays a significant role in the global nitrogen–sulfur cycle.