[Quantitative studies of Salmonella at two sewage purification plants in Schleswig-Holstein]

Quantitative Salmonella counts in different stages of the sewage treatment plants of Kiel (Bülk) and Plön in Schleswig-Holstein (FRG) were measured during a one-year-period. In weekly alternation the samples have been collected before and after each clarification step. Afterwards the Salmonella were analysed by a combined method (membrane-filtration, multistep enrichment, mpn). The inflows of the plants contained Salmonella in 98%. The treatment plant of Bülk reduced the Salmonella numbers around 89% while a reduction of 97% could be found at Plön. The most important step of the treatment for this reduction was the final sedimentation. The chemical precipitation at Plön declined the Salmonella numbers around further 87%. According to the seasonal fluctuations of the temperature of air and water the Salmonella values increased or decreased, respectively. This tendency was more impressive than it could be expected looking at the seasonal epidemiology of salmonellosis. In spite of the existing of separate sewerage systems in both towns rain led to increasing volumes of sewage. During the warmer period of the year this effect resulted in counts above average, while in wintertime - possibly caused by dilution and the salinity by roadsalt very low Salmonella numbers could be found in both treatment inflows.