title: Nitrous oxide production by lithotrophic ammonia-oxidizing bacteria and implications for engineered nitrogen-removal systems.
abstract: Chemolithoautotrophic AOB (ammonia-oxidizing bacteria) form a crucial component in microbial nitrogen cycling in both natural and engineered systems. Under specific conditions, including transitions from anoxic to oxic conditions and/or excessive ammonia loading, and the presence of high nitrite (NO₂⁻) concentrations, these bacteria are also documented to produce nitric oxide (NO) and nitrous oxide (N₂O) gases. Essentially, ammonia oxidation in the presence of non-limiting substrate concentrations (ammonia and O₂) is associated with N₂O production. An exceptional scenario that leads to such conditions is the periodical switch between anoxic and oxic conditions, which is rather common in engineered nitrogen-removal systems. In particular, the recovery from, rather than imposition of, anoxic conditions has been demonstrated to result in N₂O production. However, applied engineering perspectives, so far, have largely ignored the contribution of nitrification to N₂O emissions in greenhouse gas inventories from wastewater-treatment plants. Recent field-scale measurements have revealed that nitrification-related N₂O emissions are generally far higher than emissions assigned to heterotrophic denitrification. In the present paper, the metabolic pathways, which could potentially contribute to NO and N₂O production by AOB have been conceptually reconstructed under conditions especially relevant to engineered nitrogen-removal systems. Taken together, the reconstructed pathways, field- and laboratory-scale results suggest that engineering designs that achieve low effluent aqueous nitrogen concentrations also minimize gaseous nitrogen emissions.
authors: Department of Earth and Environmental Engineering, Columbia University, 500 West 120th Street, New York, NY 10027, USA. kc2288@columbia.edu
authors: Kartik
authors: K
authors: Chandran
authors: Lisa Y
authors: LY
authors: Stein
authors: Martin G
authors: MG
authors: Klotz
authors: Mark C M
authors: MC
authors: van Loosdrecht
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D052818:Autotrophic Processes; D001419:Bacteria / Q000378:metabolism*; D052918:Environmental Restoration and Remediation / Q000379:methods*; D009584:Nitrogen / Q000302:isolation & purification*; D009609:Nitrous Oxide / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D000641:Ammonia; D009609:Nitrous Oxide; D009584:Nitrogen