title: Inhibitory effects of nitrogen oxides on a mixed methanogenic culture.
abstract: The effect of nitrate, nitrite, nitric oxide (NO), and nitrous oxide on a mixed, mesophilic (35 degrees C) methanogenic culture was investigated. Short-term inhibition assays were conducted at a concentration range of 10-350 mg N/L nitrate, 17-500 mg N/L nitrite, 0.02-0.8 mg N/L aqueous NO, and 19-191 mg N/L aqueous nitrous oxide. Simultaneous methane production and N-oxide reduction was observed in 10 and 30 mg N/L nitrate and 0.02 mg N/L aqueous NO-amended cultures. However, addition of N-oxide resulted in immediate cessation of methanogenesis in all other cultures. Methanogenesis completely recovered subsequent to the complete reduction of N-oxides to nitrogen gas in all N-oxide-amended cultures, with the exception of the 500 mg N/L nitrite- and 0.8 mg N/L aqueous NO-amended cultures. Partial recovery of methanogenesis was observed in the 500 mg N/L nitrite-amended culture in contrast to complete inhibition of methanogenesis in the 0.8 mg N/L aqueous NO-amended culture. Accumulation of volatile fatty acids was observed in both cultures at the end of the incubation period. Among all N-oxides, NO exerted the most and nitrate exerted the least inhibitory effect on the fermentative/methanogenic consortia. The effect of multiple additions of nitrate (300 mg N/L) on the same methanogenic culture was also investigated. Long-term exposure of the methanogenic culture to nitrate resulted in an increase of N-oxide reduction rates and decrease of methane production rates, which was attributed to changes in the microbial community structure due to nitrate addition.
authors.affiliation: School of Civil and Environmental Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332-0512, USA.
authors.forename: A Evren
authors.initials: AE
authors.lastname: Tugtas
authors.forename: Spyros G
authors.initials: SG
authors.lastname: Pavlostathis
mesh_terms: D019149:Bioreactors / Q000382:microbiology; D052837:Chemoautotrophic Growth; D008697:Methane / Q000096:biosynthesis*; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D009589:Nitrogen Oxides / Q000378:metabolism*
chemical_list: D009589:Nitrogen Oxides; D009584:Nitrogen; D008697:Methane