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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.

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Discussion

The presence of protozoa in incoming wastewater will result in their presence in sludge. In this study the densities of Cryptosporidium oocysts were very low in the raw wastewater and oocysts could just be recovered from the sludge in a few samples. The densities of Giardia were higher, also reflecting their concentration in the sludge. The risks from e.g. Giardia in sludge have previously been acknowledged although the focus on protozoa has rather been on their occurrence in drinking water and raw water and not on potential sources of contamination. The densities in the different wastewater fractions reflect the incidence in the population and it is clear that wastewater and untreated sludge may pose a risk to exposed individuals in addition to being a source of contamination of surface waters.

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