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.
- Biological nutrient removal
- Dissimilatory nitrate reduction to ammonium (DNRA)
- Methanogenic inhibition
- Upflow anaerobic sludge blanket (UASB)
ASJC Scopus subject areas
- Environmental Engineering
- Environmental Chemistry