After the commissioning of the WWTP in the Causeni city and the development of the aerobic and anoxic microflora, two variants of the technological processes for removal of nitrogen compounds were tested to ensure the maximum possible treatment efficiency. First of all, in order to estimate the processes that take place in each bioreactor of the WWTP complex in the Causeni city and the effects of nitrogen migration in different forms, research and laboratory investigations of CCOCr, NO2-, NO3-, NH4+, preliminary analysis of the dynamics of change of forms of mineral nitrogen (NH4+ ↔ NO2- ↔ NO3-↔ ... ↔N2) in the solid phase and water after separation (liquid phase) of wastewater throughout the whole treatment course. The first variant tested with the prolonged aeration treatment (sludge age 24-30 days, dose by volume 130-100 mL, dose by weight 2.71-3.21 g/dm3) demonstrated an insufficient efficacy, which is not complies with the rules for discharge of NH4+ and NO2- into the aquatic environment. The elimination of organic substances and nitrification take place completely, and during the period when the loading of organic substances take place as a result of the activity of an economic agent (cannery) in the area, the denitrification takes place only in the secondary decanter, being unacceptable and leading to an unstable treatment process due to sludge flotation. The second variant tested, with the inclusion in the treatment of the ―aeration – anoxic – aeration‖ zone (sludge age 30 days, dose by volume 130-190 mL, dose by weight 2.9-3.4 g/dm3), showed a sufficient efficiency. In this case, however, the quality of the treated water does not fall within the norms of discharge into the aquatic environment only towards NO2-. This is explained by the lack of oxygen in the biofilter, due to technical reasons of air aggregates and can be overcome by their adjusting. At oxygen deficiency below 2 mg/dm3, the rate of multiplication of the bacterial mass at the first stage of nitrification NH4+ → NO2- is higher than the rate of multiplication of the bacterial mass at the second stage NO2- → NO3-, as a result the accumulation of nitrites in treated waters. In order to increase the sustainability of the technological process and to ensure wastewater at discharge with the quality corresponding to the existing norms even during periods of flow fluctuations or pollutant loading, WWTP Causeni will adjust the technological equipment for testing the third variant after implementing advanced UCT technology developed by the University of Cape Town for the elimination of biogenic substances and its intensification through the carousel regime. The consistency of anaerobic and aerobic treatment has been shown not to significantly increase the elimination effect of biogenic substances. The inclusion in the consecutive scheme of the biological treatment of the anoxic area amplifies this effect in the same technological volumes with the reduction of the air consumption for aeration by using oxygen from nitrates.