Effects of ammonium and/or sulfide on methane production from acetate or propionate using biochemical methane potential tests.

The inhibitory effects of ammonium and sulfide on the methane production using acetate or propionate as a carbon source were investigated under different pH and temperature conditions. The methane production rate, duration of the lag phase, and inhibition threshold limit during methane production were estimated using the Gompertz equation and inhibitor mathematical model. The methane production rates at 53°C were 2.3-2.7 times higher than those at 35°C in the case of non-inhibitors. Increasing the NH and/or S concentration decreased the methane production rate and increased the duration of the lag phase. For methane fermentation that was not acclimated to high NH concentration, the critical NH concentration beyond which methane fermentation would stop was 4000-5650 mg/L, depending on the pH, temperature, and carbon source. When NH and S were coexistent, the critical NH concentration decreased to approximately 3800 mg/L when propionate was used and to approximately 4450 mg/L when acetate was used. However, no synergistic effect of NH and S on the methane production rate was found at an NH concentration of < 5000 mg/L and S concentration of 50 mg/L.