title: Nitrate and nitrite inhibition of methanogenesis during denitrification in granular biofilms and digested domestic sludges.
abstract: Anaerobic bioreactors that can support simultaneous microbial processes of denitrification and methanogenesis are of interest to nutrient nitrogen removal. However, an important concern is the potential toxicity of nitrate (NO(3) (-)) and nitrite (NO(2) (-)) to methanogenesis. The methanogenic toxicity of the NO (x) (-) compounds to anaerobic granular biofilms and municipal anaerobic digested sludge with two types of substrates, acetate and hydrogen, was studied. The inhibition was the severest when the NO (x) (-) compounds were still present in the media (exposure period). During this period, 95% or greater inhibition of methanogenesis was evident at the lowest concentrations of added NO(2) (-) tested (7.6-10.2 mg NO(2) (-)-N l(-1)) or 8.3-121 mg NO(3) (-)-N l(-1) of added NO(3) (-), depending on substrate and inoculum source. The inhibition imparted by NO(3) (-) was not due directly to NO(3) (-) itself, but instead due to reduced intermediates (e.g., NO(2) (-)) formed during the denitrification process. The toxicity of NO (x) (-) was found to be reversible after the exposure period. The recovery of activity was nearly complete at low added NO (x) (-) concentrations; whereas the recovery was only partial at high added NO (x) (-) concentrations. The recovery is attributed to the metabolism of the NO (x) (-) compounds. The assay substrate had a large impact on the rate of NO(2) (-) metabolism. Hydrogen reduced NO(2) (-) slowly such that NO(2) (-) accumulated more and as a result, the toxicity was greater compared to acetate as a substrate. The final methane yield was inversely proportional to the amount of NO (x) (-) compounds added indicating that they were the preferred electron acceptors compared to methanogenesis.
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Qais
authors.initials: Q
authors.lastname: Banihani
authors.forename: Reyes
authors.initials: R
authors.lastname: Sierra-Alvarez
authors.forename: James A
authors.initials: JA
authors.lastname: Field
mesh_terms: D018441:Biofilms; D002947:Cities; D004583:Electrons; D006859:Hydrogen / Q000378:metabolism; D008697:Methane / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D012722:Sewage / Q000382:microbiology*; D014866:Waste Products / Q000032:analysis*
chemical_list: D009566:Nitrates; D009573:Nitrites; D012722:Sewage; D014866:Waste Products; D006859:Hydrogen; D009584:Nitrogen; D008697:Methane