Microbiological quality of sewage sludge in Greece disposed for agricultural use

For the disposal of sewage, sludge landfill is currently the practice adopted in Greece. Thirteen wastewater treatment plants located throughout Greece (islands excluded) were investigated over a period of 1 year in order to determine sludge microbiological quality. The time of exposure of the samples to environmental conditions and stress varied considerably, from a few hours to several months. The mean values for total coliforms were 4 to > 2400/100 ml and for faecal coliforms < 3 to > 2400/100. Salmonellae were isolated from all plants with the exception of two. Parasites were isolated from five treatment plants. There was no difference in the bacterial indicator counts of faecal pollution or the presence of salmonellae and parasites according to the time of disposal of the sludge to the fields. The samples taken from the soil, or from flowers and vegetables which grow in the area of the sludge disposal were mostly negative for faecal pollution bacteria indicators. Salmonellae and parasites were not recovered from any samples. Five of the 16 serotypes reported from the National Salmonella Reference Center were present in the sludge samples.