title: Predicting N2O emissions from nitrifying and denitrifying biofilms: a modeling study.
abstract: Wastewater treatment plants can be significant sources of nitrous oxide (N2O), a potent greenhouse gas. While our understanding of N2O emissions from suspended-growth processes has advanced significantly, less is known about emissions from biofilm processes. Biofilms may behave differently due to their substrate gradients and microbial stratification. In this study, we used mathematical modeling to explore the mechanisms of N2O emissions from nitrifying and denitrifying biofilms. Our ammonia-oxidizing bacteria biofilm model suggests that N2O emissions from biofilm can be significantly greater than from suspended-growth systems. The driving factor is the diffusion of hydroxylamine, a nitrification intermediate, from the aerobic to the anoxic regions of the biofilm. The presence of nitrite-oxidizing bacteria further increased emissions. For denitrifying biofilms, our results suggest that emissions are generally greater than for suspended-growth systems. However, the magnitude of the difference depends on the bulk dissolved oxygen, chemical oxygen demand, and nitrate concentrations, as well as the biofilm thickness. Overall, the accumulation and diffusion of key intermediates, i.e. hydroxylamine and nitrite, distinguish biofilms from suspended-growth systems. Our research suggests that the mechanisms of N2O emissions from biofilms are much more complex than suspended-growth systems, and that emissions may be higher in many cases.
authors.affiliation: Department of Civil and Environmental Engineering and Earth Science, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, USA E-mail: rnerenbe@nd.edu.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Sabba
authors.affiliation: Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 67, Delft 2628 BC, The Netherlands.
authors.forename: Cristian
authors.initials: C
authors.lastname: Picioreanu
authors.affiliation: 8922 Green Valley Drive, Theodore, AL 36582, USA.
authors.forename: Joshua P
authors.initials: JP
authors.lastname: Boltz
authors.affiliation: Department of Civil and Environmental Engineering and Earth Science, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, USA E-mail: rnerenbe@nd.edu.
authors.forename: Robert
authors.initials: R
authors.lastname: Nerenberg
mesh_terms: D020562:Betaproteobacteria / Q000254:growth & development*; D018441:Biofilms / Q000254:growth & development*; D019149:Bioreactors / Q000382:microbiology*; D058440:Denitrification; D004058:Diffusion; D019811:Hydroxylamine / Q000737:chemistry; D008962:Models, Theoretical; D058465:Nitrification; D009573:Nitrites / Q000032:analysis; D009609:Nitrous Oxide / Q000032:analysis*; D010100:Oxygen / Q000032:analysis; D062065:Wastewater / Q000737:chemistry / Q000382:microbiology
chemical_list: D019811:Hydroxylamine; D009573:Nitrites; D009609:Nitrous Oxide; D010100:Oxygen; D062065:Wastewater