[Epidemiology of salmonellae and fertilizing of grasland with sewage sludge (author's transl)]

Abstract

Our investigations prove that sludge contains Salmonellae in more than 90% of samples. The maximum number of organisms reached 10(7) per liter. One of our most important findings was the fact that neither aerobic stabilization nor anaerobic digestion significantly reduces the contamination with Salmonellae. Moreover we found that Salmonellae in sewage sludge spread on grass may survive up to 72 weeks. Fertilizing with unsanitized sludge may therefore lead to transmission from plant to animal. The increasing number of Salmonella carriers among our herds of cattle and their striking accumulation during the grazing period demonstrate that such transmission represents a growing danger. Sanitizing of sludge to be used as fertilizer is therefore urgent. We have investigated the sanitary effect of pasteurisation and of gamma irradiation on sewage sludge. After a proper pasteurisation in 5 plants (70 degrees C for 30 minutes) 98-100% of tested sludge samples contained less than 10 Enterobacteriaceae per gramm. The application of 300 krad resulted in a percentage of 97.2% of samples with less than 10 Enterobacteriaceae per gramm.