[Emission of microorganisms from sewage treatment plants depending upon construction differences of single structural parts].

In order to examine the influence exerted by the differing design of individual water treatment plant units on the emission rate of micro-organisms and the associated degree of exposure to which plant personnel is subjected, measurements were taken at three different types of treatment plants. Measurements were made using "Biotest" RCS Air Samplers. The total count of colonies was determined by means of Agar Strips GK-A (tryptic soy agar). Enterobacteriaceae were quantitatively ascertained using Agar Strips C (MacConkey agar), particular attention being paid to the determination of the coliform bacteria as faeces indicators. Agar Strips S (mannitol salt agar) were used to measure the count of staphylococci using Agar Strips HS (rosa Bengal streptomycin agar). Before taking measurements, the prevailing climatic conditions were recorded. It could be ascertained that the enclosure of the inflow area (screw conveyor pump station and aerated grit removal tank) lead to a considerable increase in the concentration of microorganisms in the air within the housing. The values dropped however, when adequate ventilation was provided. Differing oxygen in the activated sludge tanks - finebubble aeration at the tank bottom or the blowing in of air via centrifugal blowers - lead to large variations in the emission rates. However, the less the waste water is agitated, the lower the emission rates. In the case of fine-bubble aeration, rates which are also normally to be found in the "non-burdened" outside air were even recorded close to the aeration tank. In cases of centrifugal blower, the aeration tank should be covered with a shield. With this type of aeration the waste water is emitted radially towards the walls of the tank. The use of a sprinkler unit on an aeration tank equipped with centrifugal blower - to avoid foam formation on the surface of the water - does not lead to an increase in the already high emission rate. An increase in air pollution through mould fungi from waste water treatment plants could not be found. In conclusion, it can be said that different individual plant unit designs have a large influence on the concentration of micro-organisms in the ambient air of places of work of waste water treatment plant personnel. Emission rates can be limited to such a degree that, even in the immediate vicinity of the plant units, a decrease of micro-organism concentrations can be attained as comparable to the area outside the treatment plant.