Nitrate and nitrite inhibition of methanogenesis during denitrification in granular biofilms and digested domestic sludges

Research output: Contribution to journalArticlepeer-review

58 Scopus citations


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 (NO3-) and nitrite (NO2-) to methanogenesis. The methanogenic toxicity of the NOx- 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 NOx- 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 NO2- tested (7.6-10.2 mg NO2--N l-1) or 8.3-121 mg NO3--N l-1 of added NO3-, depending on substrate and inoculum source. The inhibition imparted by NO3- was not due directly to NO3- itself, but instead due to reduced intermediates (e.g., NO2-) formed during the denitrification process. The toxicity of NOx- was found to be reversible after the exposure period. The recovery of activity was nearly complete at low added NOx- concentrations; whereas the recovery was only partial at high added NOx- concentrations. The recovery is attributed to the metabolism of the NOx- compounds. The assay substrate had a large impact on the rate of NO2- metabolism. Hydrogen reduced NO2- slowly such that NO2- 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 NOx- compounds added indicating that they were the preferred electron acceptors compared to methanogenesis.

Original languageEnglish (US)
Pages (from-to)801-812
Number of pages12
Issue number6
StatePublished - Oct 2009


  • Biological nutrient removal
  • Denitrification
  • Dissimilatory nitrate reduction to ammonium (DNRA)
  • Methanogenic inhibition
  • Upflow anaerobic sludge blanket (UASB)

ASJC Scopus subject areas

  • Environmental Engineering
  • Microbiology
  • Bioengineering
  • Environmental Chemistry
  • Pollution


Dive into the research topics of 'Nitrate and nitrite inhibition of methanogenesis during denitrification in granular biofilms and digested domestic sludges'. Together they form a unique fingerprint.

Cite this