Wastewater from human settlements contains a significant amount of organic and biogenic substances. Insufficiently treated wastewater enters surface water and leads to their eutrophication. The usage of microalgae in wastewater treatment has significant advantages in comparison with other methods of removing biogenic substances. Namely: effective and simultaneous removal of nitrogen and phosphorus without reagents management facilities, oxygen formation. Using microalgae in wastewater treatment is a new environmentally friendly biotechnological method. Microalgae grow well in wastewater, from which they absorb pollutants. The purpose of the study is to analyze the work and determine the possibility of intensification of sewage treatment plants in the western region of Ukraine with a population of about 18,900 inhabitants. Productivity of treatment plant is 3400 m3/day. Experimental investigation consisted in adding a concentrate of a living microalgae strain of the species Chlorella vulgaris to the wastewater that was entered to the treatment plant during May-September 2019. During the research, the results of wastewater analyzes conducted by the chemical laboratory of the municipal water supply and sewerage company were used. The results of the survey and analysis of the city's treatment plant indicate an insufficient degree of wastewater treatment. The effectiveness of Chlorella vulgaris at the treatment plant has been experimentally proven. Mathematical dependences of the effect of wastewater treatment (using Chlorella vulgaris) on their temperature according to the indicators: BOD5, COD, concentration of ammonium nitrogen, phosphates and suspended solids were obtained. Dependencies are described by a linear function that characterizes the general behavior of the obtained data. The obtained results made it possible to significantly reduce the negative impact of treatment plants on the environment.