Wastewater treatment plants affect the environment in many different ways. It can be assumed that the intensity and range of microbiological emission is the crucial factor in determining the range of restricted-usage zone. This paper presents emission levels of microbiological pollutants from the wastewater treatment plant in Bartoszyce, Poland. It is a new plant with multifunctional activated-sludge tanks where wastewater is aerated by horizontal-axis aerators. The study has shown that aeration tanks constitute a significant source of biological aerosols emission. Considerably smaller amounts of microorganisms are emitted into the atmosphere from wastewater-collection posts and secondary settling tanks.