The flotation process of organic residues from wastewater treatment is explained by the formation of micro-bubbles of molecular nitrogen or nitrous oxide with the decrease in the density of suspended particles. A large difference in the size of micro-bubbles, formed in suspension in the vicinity of organic particles and those formed during the denitrification process in the aqueous part of the dispersed system with the release of large amounts of molecular nitrogen or N2O, has been established. The formation of gas bubbles in solution is a spontaneous and intensive process that generates a destructive agitation of the float, by dispersing and fragmenting the suspended system. Thus, it is necessary to regulate the formation of micro-bubbles and stop the process of spontaneous denitrification in the separation water. Depending on the formation and control of micro-bubbles on the flotation process, three types of flotation systems have been identified. The first type consists of combining primary sediment (PS) and activated sludge (AS) in certain proportions. For the WWTP Chisinau, where the flotation process has optimal indices, this ratio is in the ranges of 15%-20% SP and 85%-80% NA. The optimal temperature range is 41 – 45 °C, an intermediate temperature range between the mesophilic and thermophilic process, therefore characteristic for the mesothermophilic process. It should be noted that the preparations used in the technology of the aforementioned station to reduce the smell of organic residues, have an effect of suppressing the flotation process. The use of preparations to stop the sulphate-reduction process, i.e. to capture hydrogen sulphide (H2S) and mercaptans (R-SH) in PS and return the centrifugation water leads to the loss of the flotation effect. The experiments carried out prove that the odor reduction preparations suppress the effect of micro-bubble formation following the denitrification process, the protein sulfur in the AS granules having a regulatory role. The second type of float occurs with old AS. The aging period is about 7-11 hours, when the remaining dissolved oxygen is consumed and a process of denitrification or combining the amount of remaining ammonium with nitrite and nitrate ions is still possible. The latter become a source of oxygen both for the oxidation of ammonium and for the reduction of nitrites and nitrates due to decomposing organic matter. A third type of flotation occurs when using preparations to suppress sulfur reduction and capture sulfur sulfide (H2S) and mercaptan (R-SH). The sulfur fixation process initially occurs in the liquid part of the dispersed system. Then there is the formation of gas micro-bubbles, generated and regulated due to the sulfur in the bacterial proteins fixed in the AS granules.