Nitrous Oxide Production in Co- Versus Counter-Diffusion Nitrifying Biofilms

For the application of biofilm processes, a better understanding of nitrous oxide (N(2)O) formation within the biofilm is essential for design and operation of biofilm reactors with minimized N(2)O emissions. In this work, a previously established N(2)O model incorporating both ammonia oxidizing bacteria (AOB) denitrification and hydroxylamine (NH(2)OH) oxidation pathways is applied in two structurally different biofilm systems to assess the effects of co- and counter-diffusion on N(2)O production. It is demonstrated that the diffusion of NH(2)OH and oxygen within both types of biofilms would form an anoxic layer with the presence of NH(2)OH and nitrite ( [Image: see text]), which would result in a high N(2)O production via AOB denitrification pathway. As a result, AOB denitrification pathway is dominant over NH(2)OH oxidation pathway within the co- and counter-diffusion biofilms. In comparison, the co-diffusion biofilm may generate substantially higher N(2)O than the counter-diffusion biofilm due to the higher accumulation of NH(2)OH in co-diffusion biofilm, especially under the condition of high-strength ammonium influent (500 mg N/L), thick biofilm depth (300 μm) and moderate oxygen loading (~1–~4 m(3)/d). The effect of co- and counter-diffusion on N(2)O production from the AOB biofilm is minimal when treating low-strength nitrogenous wastewater.