[Qualitative and quantitative determination of bacterial populations in aquatic habitats. 5. Comparison of 2 rapid sand filters].

The bacterial examinations of raw water and the effluent of two rapid sand filters showed differences with respect to the colony count, the identified species and the activity of the isolated bacteria. The raw waters of the treatment plants Si and Me are originated from an oligotrophic artificial lake and from ground-water respectively. The two raw waters contained only low numbers of bacteria, whereas the effluents of the filters showed a considerable increase of the bacterial counts. The results indicate a development of microbial populations in the filters. Furthermore there were also differences between the two filters examined. The first one led to the growth of Pseudomonas- and Flavobacterium species, the second one to Flavobacterium, Chromobacterium and Acinetobacter species. Comparing the raw water and the effluent, a reduction of special and total physiological activities of the isolated bacteria could be observed in filter I, whereas there wasn't any change in filter II.