Evaluation of microbiological quality of atmospheric air in a selected sewage treatment plant in Lesser Poland

The adverse impact of sewage treatment plants on the environment, resulting from the emission of harmful biological agents to the atmosphere, depends mainly on the size of the facility, the quantity and composition of treated sewage as well as the technologies and equipment used. The aim of the conducted research was to determine the microbiological quality of atmospheric air at Municipal-Industrial Sewage Treatment Plant in Oświęcim, which is one of the largest treatment plants in Lesser Poland. Bioaerosol measurements were made at four points (raw sewage inlet, aeration chamber, purified sewage outlet and 150 m from the treatment plant, at the background point) in the period from January to December 2018. Bioaerosol samples were collected using Microbiological Air Sampler MAS-100 by Merck. The tested atmospheric air was characterized by a qualitatively and quantitatively diverse microflora. The largest source of emission of microorganisms to the atmosphere was the mechanical part of the sewage treatment plant (raw sewage inlet) and the biological reactor. The highest number of mesophilic bacteria was observed near the biological reactor (in the summer), the least at the control point. During the research, the least β-hemolytic bacteria was isolated at the purified sewage outlet—on average 3 CFU m−3, the highest at the biological reactor 16 CFU m−3. Most of α-hemolytic bacteria was observed near the raw sewage inlet and was not found at the control point. Actinomycetes also occurred in a small amount (0–40 CFU m−3). A high concentration of mildew fungi occurred in summer when the air temperature was highest, the smallest quantities of these microorganisms were found in January and February.