The anaerobic oxidation of ammonium

Abstract

From recent research it has become clear that at least two different possibilities for anaerobic ammonium oxidation exist in nature. 'Aerobic' ammonium oxidizers like Nitrosomonas eutropha were observed to reduce nitrite or nitrogen dioxide with hydroxylamine or ammonium as electron donor under anoxic conditions. The maximum rate for anaerobic ammonium oxidation was about 2 nmol NH4+ min-1 (mg protein)-1 using nitrogen dioxide as electron acceptor. This reaction, which may involve NO as an intermediate, is thought to generate energy sufficient for survival under anoxic conditions, but not for growth. A novel obligately anaerobic ammonium oxidation (Anammox) process was recently discovered in a denitrifying pilot plant reactor. From this system, a highly enriched microbial community with one dominating peculiar autotrophic organism was obtained. With nitrite as electron acceptor a maximum specific oxidation rate of 55 nmol NH4+ min-1 (mg protein)-1 was determined. Although this reaction is 25-fold faster than in Nitrosomonas, it allowed growth at a rate of only 0.003 h-1 (doubling time 11 days). 15N labeling studies showed that hydroxylamine and hydrazine were important intermediates in this new process. A novel type of hydroxylamine oxidoreductase containing an unusual P468 cytochrome has been purified from the Anammox culture. Microsensor studies have shown that at the oxic/anoxic interface of many ecosystems nitrite and ammonia occur in the absence of oxygen. In addition, the number of reports on unaccounted high nitrogen losses in wastewater treatment is gradually increasing, indicating that anaerobic ammonium oxidation may be more widespread than previously assumed. The recently developed nitrification systems in which oxidation of nitrite to nitrate is prevented form an ideal partner for the Anammox process. The combination of these partial nitrification and Anammox processes remains a challenge for future application in the removal of ammonium from wastewater with high ammonium concentrations.

Enrichment and characterization of an anammox bacterium from a rotating biological contactor treating ammonium-rich leachate

“…This organism was also postulated to couple the oxidation of nitrite to nitrate for generating reducing equivalents for CO 2 fixation ( Van de Graaf et al 1997). Candidatus B. anammoxidans grows slowly and has been reported to have a doubling time of 11 days at pH 8 and 40°C (Jetten et al 1999). The advantages of the anammox process over the traditional combination of nitrification and denitrification for wastewater treatment are lower oxygen demand, which is needed by nitrifiers for partial oxidation of ammonium to nitrite, and no requirement for external carbon sources because the process is autotrophic.…”

“…The basic physiological aspects of the anammox process have been studied in depth mostly by a single research group in Delft (Jetten et al 1999). However, anammox activity has been suspected for other wastewater treatment plants with uncharacterized high ammonium losses (Helmer and Kunst 1998;Siegrist et al 1998;Schmid et al 2000).…”

A Gas Chromatographic Method for the Determination of Bicarbonate and Dissolved Gases

“…In contrast, nitrous oxide concentrations were greatest in river and municipal sewage while it was virtually undetectable in swine waste. This was not unexpected given that nitrous oxide is not formed in anaerobic conditions in the absence of exogenous electron acceptors that sustain anaerobic respiration (Jetten et al, 1999). No significant changes in measured bicarbonate concentrations were seen in samples over 5 weeks of storage (Figure 1).…”

Autotrophic ammonia removal from landfill leachate using anaerobic membrane bioreactor

“…Heavy metals are not easily biodegradable and can accumulate in organisms, causing biological accumulation toxicity. While there are few studies on the heavy-metal inhibition of ANAMMOX, in general about 1 mmol L -1 HgCl 2 fully inhibited ANAMMOX activity [22].…”