Abstract
From discovery in the early 1990s to completion of full-scale anammox reactor, it took almost two decades to uncover the secret veil of anammox bacteria. There were three milestones during the commercialization of anammox: the development of the first enrichment culture medium, the completion of the first commercial anammox reactor, and the fast start-up of full-scale anammox plant. Till now, the culture of anammox bacteria experienced a big progress through two general strategies: (a) to start up a reactor from scratch and (b) to seed the reactor with enriched anammox sludge. The first full-scale anammox reactor took 3.5 years to realize full operation using the first approach due to several reasons besides the lack of anammox sludge. On the other hand, the first Asian anammox reactor started up in two months, thanks to the availability of anammox seed. Along with the implementation of anammox plants, anammox eventually becomes the priority choice for ammonium wastewater treatment.
Highlights
Conventional biological nitrogen removal from wastewater usually consists of two steps, nitrification and denitrification
Anammox bacteria oxidize ammonium to nitrogen gas using nitrite as an electron accepter under anoxic conditions, and their growth occurs by carbon dioxide fixation (Table 1) [8]
Nitrite is reduced to hydroxylamine at the cytoplasmic site of the same enzyme complex responsible for hydrazine oxidation with an internal electron transport (Figure 3(a)). Another possible mechanism for anammox process is concluded as follows: ammonium and hydroxylamine are converted to hydrazine by a membrane-bound enzyme complex, hydrazine is oxidized in the periplasm to dinitrogen gas, and the generated electrons are transferred via an electron transport chain to nitrite reducing enzyme in the cytoplasm where nitrite is reduced to NH2OH (Figure 3(b))
Summary
Conventional biological nitrogen removal from wastewater usually consists of two steps, nitrification and denitrification. Ammonium is biologically oxidized to nitrate, which is reduced to nitrogen gas using organic matter as electron donor during denitrification process. The surplus sludge generated in conventional biological nitrogen removal process increases the treatment cost. Anaerobic Ammonium Oxidation (anammox) is a novel, autotrophic, and cost-effective alternative to the traditional biological nitrogen removal process [5,6,7]. Anammox bacteria oxidize ammonium to nitrogen gas using nitrite as an electron accepter under anoxic conditions, and their growth occurs by carbon dioxide fixation (Table 1) [8]. The discovery of anammox process brought revolutionary changes to conventional biological nitrogen removal from wastewater. N2 paid on the commercialization and full-scale application of anammox technique
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