EFFECT OF AMMONIA INHIBITION IN THERMOPHILIC ANAEROBIC PROCESS

The inhibition effects of total ammonia nitrogen (TAN) on acetotrophic methanogenic activity using biomass from two thermophilic anaerobic reactors were investigated in this study. The biomass was acclimated at different background levels of TAN before Anaerobic Toxicity Assay (ATA) were conducted. The TAN background concentrations in the reactors were 400, and 1,200 mg/L. The digester operated with a TAN concentration of 400 mg/L, showed a similar system performance to the digester operated at a TAN of 1,200 mg/L in terms of chemical oxygen demand (COD) removal and methane yield. The results from the ATA indicated: 1) The TAN concentrations higher than 2,000 and 4,000 mg/L began to cause inhibition on acetotrophic methanogens of the biomass from the reactors acclimated to the TAN concentrations of 400 and 1,200 mg/L, respectively. 2) The lethal TAN concentration of methanogens was approximately 10,500 mg/L, independent of pH and background TAN concentrations. 3) At a constant TAN concentration, methanogenic activities varied with the pH values. The highest methanogenic activities were observed at pH of 7.5 for the biomass from both reactors. 4) It was also observed that methanogenic activities at TAN of 400 mg/L were consistently lower comparing to the biomass acclimated to 1,200 mg/L of TAN.