Biological denitrification characteristics of pure cultures isolated from methane-utilizing mixed culture

Abstract

The characteristics of growth and nitrate reduction of a stable methaneutilizing mixed culture, obtained from activated sludge by selective enrichment culture, were investigated in batch and continuous fermentator. The maximum specific growth rate of the culture was 0.22 (hr$^{-1}$) and the specific nitrate reduction rate was 28 (mg NO$_3^-$-N/g cell/hr) at the optimal dilution rate of 0.11 (hr$^{-1}$) and oxygen limiting condition. Since the mixed culture had a relatively high nitrite accumulation (8.5 mg NO$_2^-$-N/g cell/hr) so the pure organisms were isolated from the mixed culture to investigate the reason of nitrite accumulation. The maximum specific growth rates of mthane-, methanol- and citrate-utilizing organisms, isolated from the mixed culture by plating method, were 0.187, 0.180 and 0.480 (hr$^{-1}$), respectively. The specific nitrate reduction rates of those organisms in the continuous culture at the dilution rate of 0.11 (hr$^{-1}$) and oxygen limiting condition were 17.63, 62.4, and 14,77 (mg NO$_3^-$-N/g cell/hr) and the specific nitrite accumulation rates were 0.37, 0.10 and 0.23 (mg NO$_2^-$-N/g cell/hr), respectively. The saturation constants of the methane-utilizing organism on oxygen and methane were $1.84 \times 10^{-5}$ (g O$_2$/1), $2.27 \times 10^{-5}$ (g CH$_4$/l) and the yields were 0.6 (g cell/ g CH$_4$) and 0.18 (g cell/g O$_2$), respectively.