Employees of waste water treatment plants are always exposed to biological substances. In order to determine the micro-organism load from aerosols in waste water plants, 10 samples were taken between October 2003 and September 2004 at two different locations of a sewage system and in the grit chamber of a treatment plant. Two further samples were collected in the course of high-pressure cleaning in the relief sewer tunnel. Samples from the outside air served as controls.
The samples were collected using the impaction method with Merck® MAS-100 and the impingement method with SKC Biosampler®. Samples were collected in an altitude of 1.5m. In addition to the culturable bacteria, the number of coliform bacteria as well E. coli and mold species A. fumigatus were determined. Bacteria and A. fumigatus were cultured on blood agar, coliform bacteria and E. coli on Endo Agar and Coli ID medium.
In the sewers and the relief sewer, the highest loads of culturable bacteria were found in summer. In the encased grit chamber, the highest loads were found during winter. Coliform bacteria as well as E. coli were only found in isolated cases; A. fumigatus was found at all locations at the level of the natural ambient load of 10 CFU/m³. In the course of high pressure cleaning, total bacterial loads reached up to 4.0x104 CFU/m³ and coliform bacteria up to 3.0x10³ CFU/m³.
Prevention of exposure as well as preventative hygienic measures must be taken to guarantee the safety and health of employees as waste water-related work will lead to fecal-oral infection and to inhalation of airborne microorganisms.