Microbiological activities contributing to nitrogen removal with methane: effects of methyl fluoride and tungstate

Abstract When methane (CH 4 ) and O 2 are present, nitrogen can be removed from wastewater that does not contain other organic carbon sources. In this study, microbial activities during methane-dependent denitrification (MDD) were investigated by adding inhibitors of methane-oxidation and denitrification. Sludge susceptible to MDD showed methane oxidation activity in the presence of CH 4 and O 2 , and denitrification activity with methanol and acetate under anoxic conditions. Methyl fluoride (CH 3 F) is known to inhibit methane oxidation. When CH 3 F was present, MDD did not occur, perhaps because methane oxidation was inhibited. Tungstate (WO 4 2− ), a known inhibitor of nitrate reduction, also lowered denitrification activity in the sludge, and partly inhibited methane oxidation. When WO 4 2− was added to the medium, MDD almost ceased, perhaps because of a synergic inhibitory effect on denitrification and methane oxidation. These results show that both methane oxidation and denitrification contribute to MDD.