[Scanning electron microscopic studies of the microbial colonization of slow sand filters]

Using scanning electron microscopy (SEM), we studied the periphyton on the filter material of slow sand filters (SSF)--main basins--from the water-works in Geisecke/Ruhr. Table 1 presents information about the quantitative vertical distribution of the filter material with its size and shape, water-storage, nutrient content and the presence of bacteria. The proportion of microbial growth to microbial content was high with 80% found in the upper and about 70% in the lower part of the filter body. Larger sand particles supported proportionally higher populations than did small grains. Depressions were well populated. Heavier microbial concentrations resulted in attachment and colonization on exposed grain surfaces. Only some microorganisms adhered through slime-nets and stalks, and no sample showed any general or special mechanisms. The photographic reproduction of the effects was difficult, because of the amount of adherent organic and inorganic matter as well as the different topographic surfaces of the grains. Therefore we have not attempted a quantitative evaluation. 3 plates with SEM micrographs show the locations of colonizing bacteria on sand grains and organisms and their mode of attachment.