Anammox

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Anammox is an acronym of the words on aerobic Amm onium Ox composed idation. Anaerobic ammonium oxidation is a biological process from the area of ​​the nitrogen cycle .

As the name suggests, anaerobic ammonium oxidation is an oxidation process that takes place without oxygen ( anaerobic ). In this case, ammonium (NH 4 + ) with nitrite (NO 2 - ) under anaerobic conditions to form molecular nitrogen (N 2 ) synproportioniert :

NH 4 + + NO 2 - → N 2 + 2 H 2 O

Under standard conditions , 357.8 kJ of energy are released per mole of oxidized ammonium (ΔG 0 ' = −357.8 kJ).

Anammox organisms

The anammox reaction was first observed in the 1980s in a wastewater treatment plant in Delft , the Netherlands ( Mike Jetten ). Responsible for this is the previously little noticed bacterium Candidatus Brocadia anammoxidans . At the beginning of 2006, a European research consortium gained knowledge about the evolution and metabolism of the bacterium, which has only been known for a few years. In addition to Brocadia anammoxidans , the anammox process was also observed in the bacteria Kuenenia stuttgartiensis and Scalindua sorokinii ; while the former are freshwater organisms, Scalindua lives in the sea.

Ladderan lipids

According to its genetic makeup, Candidatus Brocadia anammoxidans is clearly one of the bacteria, but the microbes have organelles , as is actually only usual in the more complex eukaryotes (living beings with a cell nucleus). The cell wall of the purple-red bacteria, however, resembles that of archaea . Brocadia anammoxidans uses the anammox reaction to generate energy, producing the toxic intermediate hydrazine . The key enzyme of the reaction, a hydroxylamine - oxidoreductase , is located in a particular organelle , the Anammoxosom. Lipids with fused cyclobutane rings, known as “ ladderanes ” due to their ladder-like structure , give the membrane of the anammoxosome a particularly dense structure. It was originally assumed that this would prevent hydrazine from escaping from the organelle. However, this barrier effect has been refuted experimentally, and ladderans are also found in other membrane systems of anammox bacteria.

A research team led by Boran Kartal from the Max Planck Institute for Marine Microbiology in Bremen has discovered a microorganism (Candidatus Methanoperedens nitroreducens - an archaea from the order of the Methanosarcinales ) that can convert methane into carbon dioxide in anaerobic methane oxidation with the help of trivalent iron. The trivalent iron is reduced to bivalent iron, which is easily soluble in water and is therefore available to other organisms. In addition, C. Methanoperedens nitroreducens can reduce nitrate to ammonium, which in turn forms elemental nitrogen (N 2 ) in the anammox reaction without oxygen . Thus, in a bioreactor that contains two types of microorganisms, ammonium, methane and nitrate from the wastewater could be simultaneously converted into harmless elemental, molecular nitrogen and carbon dioxide, with carbon dioxide being less climate-active than methane.

Importance for wastewater treatment

The anammox process is not only of academic interest, but also offers a promising alternative to the classic method in sewage treatment plants to remove nitrogen compounds. For this reason, several patents have already been granted in connection with the Anammox process. In contrast to the microbes typical of biological clarification stages, Brocadia anammoxidans does not need any oxygen and also uses the greenhouse gas carbon dioxide . The absence of energy required for ventilation results in considerable savings potential. Although there are no reliable figures available due to the lack of operational experience with the application of the process in the main flow, savings potentials of up to 10% are forecast and at the same time the emission of carbon dioxide is reduced by up to 88%. For the development of biological processes, the studies carried out in the 1990s on the microbiological relationships between nitrification / denitrification and, in particular, the increasing knowledge of inhibiting mechanisms within nitrogen conversion, laid the basis for the development of adapted processes with targeted use of these mechanisms. Examples are the studies in Vienna (Nowak and Svardal, 1993; Nowak, 1996), Delft (van Niel et al., 1993; van Loosdrecht and Jetten, 1998) and Hanover (Abeling, 1994; Hippen, 1999). Successful use of Anammox depends on various parameters, e.g. B. on the prevailing temperatures and the age of the mud . In Germany, Anammox projects have been implemented at various sewage treatment plants since 2000, but so far they have always focused on the treatment of partial flows (e.g. sludge water treatment). So far, Anammox has only been used in Austria in the main stream deammonification at the Strass / Zillertal sewage treatment plant. This knowledge has been implemented in Rotterdam since early 2006. At this point in time there are a large number of different process systems available on the market. The extent to which they meet the requirements for economical and operationally stable operation will become apparent over the next few years with increasing experience of large-scale systems.

Another, as yet unexplored variant of anaerobic ammonium oxidation is oxidation using the anodes of bioelectrical systems. Such systems can be microbial fuel cells or microbial electrolysis cells . With the exclusion of oxygen and in the absence of nitrite or nitrate , microorganisms that populate the anodic half-cell can oxidize ammonium to form dinitrogen gas (N 2 ). The reaction product is the same as in the classic anammox process. At the same time, the released electrons are transferred to the anode and can thus generate an electrical current. This can then either be used directly in fuel cell mode or in electrolysis mode to generate hydrogen and methane gas . While the reaction mechanism is still unclear, it has been suggested that nitrite, nitrate or nitrous oxide play a role as intermediates. However, since the process also takes place at very low electrochemical potentials , other, speculative reaction mechanisms also appear to be possible.

Ecological importance

Until now, it was assumed that so-called denitrification (gradual bacterial reduction of nitrate to nitrogen gas by organic substances in the event of a lack of oxygen) is solely responsible for the release of nitrogen. The discovery of bacterial anaerobic ammonium oxidation thus has far-reaching consequences for the scientific understanding of the nitrogen cycle. Anammox in the oceans is of particular importance for the global nitrogen cycle.

The mathematical models describing the global nitrogen balance must now be revised, because this newly discovered nutrient - sink has a direct impact on the calculation of the carbon cycle and hence long-term climate assessments.

literature

  • MS Jetten et al .: 1994-2004: 10 years of research on the anaerobic oxidation of ammonium . In: Biochem. Soc. Trans. Vol. 33, 2005, pp. 119-123. PMID 15667281 .
  • MS Jetten et al .: Anaerobic ammonium oxidation by marine and freshwater planctomycete-like bacteria . In: Appl. Microbiol. Biotechnol. Vol. 63, 2003, pp. 107-14. PMID 12955353 .
  • MS Jetten et al .: Microbiology and application of the anaerobic ammonium oxidation ('anammox') process . In: Curr. Opin. Biotechnol. Vol. 12, 2001, pp. 283-288. PMID 11404106 .
  • MS Jetten et al .: The anaerobic oxidation of ammonium . In: FEMS Microbiological Reviews. Vol. 22, 1998, pp. 421-437. PMID 9990725 .
  • U. Abeling: Nitrogen elimination from industrial waste water - denitrification via nitrite , In: Series of publications by the Institute for Urban Water Management and Waste Technology at the University of Hanover . H. 86, 1994.
  • O. Nowak: Nitrification in the activated sludge process with decisive industrial wastewater influence , In: Vienna Communication . H. 135, 1996.
  • O. Nowak, K. Svardal: Observations on the kinetics of nitrification under inhibiting conditions caused by industrial wastewater compounds . In: Water Science and Technology . Vol. 28, 1993, pp. 115-123.
  • AA van de Graaf, P. de Bruijn, A. Robertson, MSM Jetten, JG Kuenen: Metabolic pathway of anaerobic ammonium oxidation on the basis of 15N studies in a fluidized bed reactor . In: Microbiology (UK) . Vol. 143, 1997, pp. 2415-2421.
  • MCM van Loosdrecht, MSM Jetten: Microbiological conversions in nitrogen removal . In: Wat. Sci. Tech. Vol. 38, 1998, pp. 1-8.
  • EWJ van Niel, A. Robertson, JG Kuenen: A mathematical description of the behavior of mixed chemostat cultures of an autotrophic nitrifier and a heterotrophic nitrifier / aerobic denitrifier; a comparison with experimental data . In: FEMS Microbiology Ecology , Vol. 102, 1993. pp. 99-108.

Web links

Individual evidence

  1. ↑ M. Strous et al .: Deciphering the evolution and metabolism of an anammox bacterium from a community genome. In: Nature . Vol. 440, No. 7085, 2006, pp. 790-794. PMID 16598256
  2. ↑ Jogler, C. (2014), The bacterial 'mitochondrium'. In: Molecular Microbiology, Vol. 94 (4), pp 751-55, doi : 10.1111 / mmi.12814 . PMID 25287615
  3. ↑ Neumann, S., et al. (2014), Isolation and characterization of a prokaryotic cell organelle from the anammox bacterium Kuenenia stuttgartiensis. In: Molecular Microbiology, Vol. 94 (4), pp 794-802, doi : 10.1111 / mmi.12816 . PMID 25287816
  4. ↑ Katharina F. Ettwig, Baoli Zhua, Daan Speth, Jan T. Keltjens, Mike SM Jetten, Boran Kartal: Archaea catalyze iron-dependent anaerobic oxidation of methane . October 24, 2016, doi : 10.1073 / pnas.1609534113 ( pnas.org ).
  5. ^ A b M. Siegert, A. Tan: Electric stimulation of ammonotrophic methanogenesis . In: Frontiers in Energy Research . 7, 2019, p. 17. doi : 10.3389 / fenrg.2019.00017 .
  6. ↑ a b A. Vilajeliu-Pons, C. Koch, MD Balaguer, J. Colprim, F. Harnisch, S Puig: Microbial electricity driven anoxic ammonium removal . In: Water Research . 130, 2018, pp. 168-175. doi : 10.1016 / j.watres.2017.11.059 .
  7. ↑ Moritz Holtappels, Phyllis Lam, Marcel MM Kuypers: The nitrogen cycle in the ocean . In: Biospectrum . Vol. 15, No. 4, 2009, pp. 368-373.