[Microbiological studies of PVC packing sheets and sediments from a wet cooling tower]

On surface of PVC packing sheets in wet cooling towers thick sediment layers can often be observed (Fig. 1) which usually cause several technological troubles. Microbiological investigations were made in order to estimate whether some hygienic risk possibly based on the proliferation of hygienic relevant microorganisms in the sediment have to be considered. An abundance of bacteria actinomycetes and fungi was found in the sediments from PVC packing sheets which were exposed for 6 or 20 weeks in a wet cooling tower (Table 2). However, the microbial (colony) counts usually decreased when the exposition time increased. Pseudomonas aeruginosa was not detected at all. Coliform bacteria and Escherichia coli showed a declining development both in the sediment and in the cooling water unter test (Table 3). Total volume of plankton also decreased in cooling water incubated with small pieces of PVC packing sheets. The results indicate the sediment formation on PVC packing sheets in wet cooling towers probably not to be problem of environmental hygiene but technology. The sediment formation seems to depend mainly of the quality (i.e. pollution degree) of cooling water and also of surface properties of the packing sheets.