Protozoan Parasites in Sewage Sludge

image of Protozoan Parasites in Sewage Sludge

A Nordic project was initiated as part of an evaluation of sludge treatment processes based on the suggested new EU legislation (EC 2000REF). This report covers the different parts of the project. The project focused on sewage and sludge treatment within a broader frame of background information regarding Giardia and Cryptosporidium, especially the relationship between the risk of transmission and the risk of aquiring infections from the environment. The objectives were further to exemplify the occurrence and viability of Giardia and Cryptosporidium through investigations in raw sewage and untreated or treated sludge from two sewage treatment plants. This report includes: 1. A literature review of Giardia and Cryptosporidium in the society and the environment. 2. A field study of occurrence and removal of the protozoa during wastewater and sludge treatment and,3. A laboratory study to further evaluate the efficiency of sludge treatment at various temperatures.




This study makes clear that viable Giardia cysts and to a lesser extent Cryptosporidium oocysts is present in high concentrations in the raw sewage and further concentrated in the raw sludge from sewage treatment facilities. The high concentrations of (oo)cysts in the sludge may be a health risk if the sludge is not properly treated. Sufficient die-off was achieved within a few days in laboratory scale experiments in both 50°C and 35°C. In 10 °C the survival was prolonged to 3 weeks. An initial dieoff was observed within the first day even in 10°C and other factors than temperature are believed to influence the inactivation. This effect did not occur in water samples. It is believed that properly treated sludge is not a significant factor for transmission of infectious (oo)cysts. The FISHmethodology was useful for Cryptosporidium in controlled laboratory experiments, but was difficult to interpret for Giardia cysts from sludge in field samples. For future studies it would be interesting to investigate the presence of different species and subtypes occurring in sludge and sewage for potential human infective transmission.


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