The activity of the microbial culture in the process of intermittent nitrification / denitrification was investigated in this thesis. Oxy / anoxy conditions were sustained during the process with the dynamic of: 0.5 hour anoxy conditions, 1 hour oxy conditions, 0.5 hour anoxy conditions, and again oxy conditions. The microbial culture has the capacity to remove nitrogen by the process of biological nitrification and denitrification. The rate of ammonia oxydation was 35 mg NH4-N removed/L,h with the pH value of 7.8. The rate of ammonia oxydation was 30 mg NH4-N removed/L,h with the pH value of 7.5. In the experiment of heterotrophic nitrification the rate of ammonia oxydation was 26.5 mg NH4-N removed/L,h. During nitrification there is a build up of both NO3-N and NO2-N. By prolonged aeration the entire NO2-N is oxidized to NO3-N. The rate of denitrification, with a surplus of a carbon source added, is 85 mg NO3-N removed/L,h. The rate of ammonia oxydation after denitrification has been performed is 27 mg NH4-N/L,h, determined as a value of ammonia oxydation only after the organic components have been spent (lowering of COD) in aerobic conditions. The rate of ammonia oxydation in the experiments of intermittent nitrification / denitrification was 36 – 40 mg NH4-N/L,h, in the phases of the process with oxy conditions. The rate of denitrification in the experiments of intermittent nitrification / denitrification was 76 – 80 mg NO3-N/L,h in all of the observed phases of the process with anoxy conditions.