Seasonal changes in the concentrations of airborne bacteria emitted from a large wastewater treatment plant

• The aim was to examine seasonal patterns in the microbiological emission.
• Wastewater and bioaerosol samples were collected in different seasons in wastewater treatment plant.
• The most intense emission was in summer, in a grit chamber and sludge storage site.
• Major emitters of microbiological contamination on wastewater treatment plants were identified.

Various factors influence the concentrations of bacteria and fungi found in the air surrounding wastewater treatment plants. These include the relative humidity, temperature, intensity of UV and visible radiation, and wind speed. Typically, higher emissions of bioaerosols are observed in the summer months due to the smaller amount of rainfall. The purpose of this study was to undertake a microbiological analysis of wastewater samples from a wastewater treatment plant (with samples taken before and after treatment) together with an analysis of bioaerosol samples taken in and around the plant. The study was undertaken in different seasons and samples were collected during a variety wastewater and sludge treatment operations. The most intense airborne emissions were found in the summer when, in most cases, all groups of bacteria (mesophilic bacteria, total coliforms, faecal coliforms and mannitol-positive staphylococci) were isolated from the air samples. The highest concentrations of airborne bacteria were observed at a grit chamber and a sludge storage site. The same seasonal trend was found in wastewater – bacteria numbers were significantly higher in the summer; mannitol-positive staphylococci were only present in treated wastewater in the summer.