The equipment has a main reaction (I) and an anterior reactor (II), as well as facilities for feeding in untreated sewage, removing cleaned water and sludge and aerating the wastewater entered into the main reactor, and a mixer (2) situated in the anterior reactor (II), and it is characterized by that between the main reactor (I) and the anterior reactor (II) there is a facility or there are facilitates for the recirculation of wastewater. In the course of the procedure, between the anterior reactor (II) and the main reactor (I) the waste-water aerated in the latter reactor and mechanically stirred in the former reactor is recirculated, and so the transformation of the nitrogen content of the biologically decomposable pollutants by nitrification takes place in the main reactor, while the biological elimination of the nitrates created in the course of the nitrification (denitrification) takes place in the anterior reactor, and as a result of the anaerobic processes biological phosphorus elimination is also ensured (FIG. 1).