IsoMol: Advanced understanding of autotrophic nitrogen removal and associated N2O emissions in mixed nitritation-anammox systems through combined stable ISOtopic and MOLecular constraints

Scientist Empa: Jing Wei (Postdoc)

Collaboration with Prof. M. F. Lehmann (University of Basel), Dr. A. Joss (Eawag Dübendorf), Dr. H. Bürgmann (Eawag Kastanienbaum)


Autotrophic nitrogen (N) removal by anaerobic ammonium oxidation (anammox) is an important mechanism of fixed N elimination, both in engineered and natural systems. In wastewater treatment plants, it may permit operation under energy autarky and with a better carbon footprint. However, its process control and engineering is still under development: An optimized removal process using nitritation-anammox systems must combine stable operation, high N removal efficiency and minimized greenhouse gas emissions. Yet the biogeochemical and microbiological controls on the production of N2O in wastewater treatment are poorly understood. Similarly, the links between system stability, activity, and microbial population shifts are not well constrained.

The collaborative and highly interdisciplinary project “IsoMol”, funded by SNSF Sinergia and led by M. F. Lehmann (Unibas), seeks to understand the functioning of mixed microbial populations featuring alternative biogeochemical pathways and to characterize its dependence on environmental conditions and microbial composition. The project consists of four sub-projects:

Subproject 1, led by A. Joss (Eawag) has a strong applied component, which includes the set-up of enriched and mixed culture nitritation-anammox reactors at the laboratory and pilot scales. It aims at understanding both process controls and N2O emission in these systems (e.g., oxygen supply and temperature), and to evaluate the benefits of anammox-based wastewater treatment with respect to conventional approaches.

Subproject 2, led by M. Lehmann (Unibas) will study ammonium, nitrite and nitrate N and oxygen O isotope fractionation with a particular focus on the isotopic effect of anaerobic nitrate formation by anammox, as well as the potential of N and O isotope measurements to diagnose chemical transformations and reaction rates for different inorganic N substrates.

Subproject 3, led by J. Mohn (Empa) will develop and test stable isotope methods to understand and identify the main processes leading to the emission of N2O across the range of typical operating conditions – in particular, with respect to a possible new pathway associated with the anammox metabolism (E. Harris et al, 2015).

Subproject 4, led by H. Bürgmann (Eawag), will make use of cutting-edge techniques in microbiology and genetics, specifically metagenomics and metatranscriptomics, to understand the structure and function of mixed-culture anammox consortia in response to key external variables, and the mechanisms that control stability.

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