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Background: The quantitative assessment and qualitative identification of moulds at workplaces in wastewater treatment plants were the aim of the study., Materials and Methods: The study was carried out in four wastewater treatment plants, where 15 stationary points were selected according to mechanical, biological and sewage sludge treatment processes. In addition, background level samples from the city area were also collected. Bioaerosols were sampled with use of a Burkard Aerosol Sampler and directly put on Malt Extract Agar plates. Identification of moulds was based on morphological properties described in the professional literature., Results: The identified concentrations of moulds were low and ranged between 0.11 and 16.75 x 10(2) cfu/m3. The highest mean levels of fungal microflora were found during sewage sludge treatment processes. In total, there were 65 fungal isolates, of which 80% were found in wastewater treatment plants. In bioaerosol samples of the occupational origin, the highest (40%) amount of isolates originated from sewage sludge treatment processes and the lowest (25%) from biological treatment stages. In wastewater treatment plants, moulds of Aspergillus genus predominated and represented nearly 35% of all identified fungi. Comparing to background levels, the content of this genus was almost 4.5 times higher. Pathogenic Aspergillus fumigatus was found at all stages of wastewater treatment and Trichophyton genus at the stage of mechanical treatment. Moreover, there were numerous moulds of Mucor, Penicillium and Alternaria genera. In background samples moulds of Penicillium genus predominated and no pathogenic species were found., Conclusions: The obtained results reveal that the sewage sludge is the main source of mould emission into the air at workplaces in wastewater treatment plants. On account of the presence of moulds with the evidenced infectious and allergic activity it is suggested that personal protective equipment should be used by employees.