In methane fermentation using high nitrogen-concentrated feedstock, inhibition by ammonia is a problem. This study aimed to reduce the amount of free ammonia and suppress inhibition by adjusting the pH in the fermenter to 6.8 to 7.3 by adding acid. Results showed that pH control by acid addition was possible and had no adverse effect on methane fermentation. In addition, even at high nitrogen concentrations with TAN of 9,000 to 11,000 mg L-1, it was possible to suppress ammonia inhibition and maintain methane production through pH control. These results suggest that methane fermentation using high nitrogen-concentrated feedstock, which has been difficult to achieve in the past, is possible, and that a high nitrogen-concentrated digestate can be obtained as a result.
