A stable coculture containing anammox and N-damo microorganisms in a laboratory scale sequencing batch reactor was suplied with oxygen. All supplied oxygen was consumed by the culture and ammonia, nitrite and nitrate removal rates were 325 ± 44 mg L-1 day-1, 456 ± 2 mg - L-1 day-1 and 27 ± 2 mg L-1 day-1, respectively. Simulteneous activity of aerobic and anaerobic ammonium- and methane oxidizing microorganisms and methanogens was measured in the culture.