Evidence for the occurrence of Feammox coupled with nitrate-dependent Fe(II) oxidation in natural enrichment cultures.

Chemosphere

State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing, 210023, China; School of the Environment, Nanjing University, Nanjing, 210023, China. Electronic address:

Published: September 2022

Feammox is a newly discovered process of anaerobic ammonium oxidation driven by Fe(III) reduction. Nitrate-dependent Fe(II) oxidation (NDFO) is the coupling of Fe(II) oxidation and nitrate reduction to produce N under anaerobic conditions. It has not been reported whether the coupling of the two reactions exists in natural enrichment. In this study, enrichment culture experiments were carrired out to prove the occurrence of Feammox with NDFO. The results indicated that the nitrogen and iron cycle were formed during natural enrichment cultures, including Fe(III) reduction and NH-N was oxidation to NO-N, NO-N and N, Fe(III) and Fe(II) were cyclically formed, and Fe(II) was oxidized with NO-N reduced to N. The removal efficiencies of ammonium nitrogen and total nitrogen in the incubation were about 92.9% and 20% respectively. Organic carbon experiments indicate that sodium acetate can promote the initial NO-N removal and a low concentration of organic carbon limited the NDFO process because iron-oxidizing bacteria are mixotrophic microorganisms. The added 9,10-anthraquinone-2,6-disulfonate (AQDS) in the later stage can promote NDFO to remove nitrate, thereby increasing the TN removal efficiency to 50%. N-isotope tracer incubations provided direct evidence for the occurrence of Feammox coupled to NDFO, with rates producing N of Feammox (0.024-0.0288 mg N·L·d) and NDFO (0.0465-0.0833 mg N·L·d) in three groups (Wetland/Wheat soil/Sediment). 16S rRNA sequencing further demonstrated that Pseudomonas, Rhodanobacter, Acinetobacter and Thermomonas were the dominant generas among the enrichment cultures, and these bacteria belonged to FeOB and FeRB, which may further promote Feammox coupled to NDFO in the cultivation system.

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http://dx.doi.org/10.1016/j.chemosphere.2022.134903DOI Listing

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