Impact of a Small Wastewater Treatment Plant on the Sanitary State of Atmospheric Air

Wastewater treatment plants are the source of odour and microorganism emissions to the atmospheric air. Bioaerosol emitted by treatment plants may contain pathogenic microorganisms, antibiotic resistant microorganisms and cause allergies. The aim of the study was to assess the impact of the newly created municipal wastewater treatment plant using the activated sludge method (approx. 20,000 PE, average daily flow of 2,300 m(3)) on the sanitary state of atmospheric air. Numerous field obstacles (e.g. trees) and natural sources of microorganism emissions to the atmospheric air (e.g. drainage channels) were located in the vicinity of the wastewater treatment plant. Bioaerosol samples (3 replicates) were taken in a wind trail at 10 test stands on the leeward side of the treatment plant and two control stands on the windward side of the treatment plant. Samples were taken by sedimentation on Petri dishes with microbiological mediums. Media was incubated at a temperature appropriate for the type of microorganisms (psychrophilic bacteria, mesophilic bacteria, actinomycetes, mold fungi), and then colonies growing on media were counted. The number of microorganisms per unit volume of air was determined according to the Omelian formula in the Gogoberidze modification. Four series of tests were carried out during the transition months (spring and autumn). The concentration of microorganisms on the leeward side of the treatment plant in the following ranges amouted: psychrophilic bacteria: 156 +/- 85 - 6578 +/- 1286 cfu/m(3), mesophilic bacteria: 87 +/- 24 - 6309 +/- 1349 cfu/m(3), actinomycetes: 0 +/- 0 - 719 +/- 12 cfu/m(3), mold fungi: 52 +/- 42 - 4645 +/- 425 cfu/m(3). These values were similar to those found in the area and in the vicinity of wastewater treatment plants examined by other authors. The concentration of microorganisms in the vicinity of the tested wastewater treatment plant did not show a downward trend as a function of distance from the wastewater treatment plant. This could be due to the presence of other sources of bioaerosol emissions to atmospheric air in the vicinity of the treatment plant (e.g. drainage canals, uncovered soil in plowed fields) and field obstacles that could have affected the movement of air masses (e.g. in-field woodland, forest, embankment Railway). The obtained research results indicate that the emission of bioaerosol from a small wastewater treatment plant, may cause changes in the concentration of microorganisms in the atmospheric air at a level close to natural sources. However, the threats to human health caused by bioaerosol emitted from municipal wastewater may be higher. Therefore, it is justified to monitor the sanitary state of the air and the atmosphere at the wastewater treatment plant and in its vicinity, and conduct research to develop an optimal set of indicator microorganisms of this state.