Ammonia inhibition on thermophilic aceticlastic methanogens.

The inhibition effects of total ammonia nitrogen (TAN) on aceticlastic methanogenic activity using biomass from thermophilic anaerobic reactors were investigated in this study. Anaerobic Toxicity Assays (ATA) were conducted after the biomass was acclimated to different levels of TAN. The TAN background concentrations in the reactors were 400, 1,200, and 3,050 mg/L. The results from ATA showed: 1) high TAN concentrations could cause inhibition of aceticlastic methanogens; 2) biomass acclimated to higher TAN concentrations could alleviate the inhibition effect due to the increase of TAN concentration; 3) the lethal TAN concentration for methanogens was approximately 10,000 mg/L regardless of the background TAN concentration; 4) ATA results also revealed the role played by pH. At a given TAN concentration, methanogenic activity varied with the pH values. The highest methanogenic activity was always observed at a pH of 7.0-7.5. 5) It was also observed that acclimation could increase the pH tolerance range, which made methanogens less sensitive to pH changes.