Different types of sewage sludge produced during wastewater treatment and after storage of up to 5 years were analyzed for both virus and parasite eggs.
Among the 145 samples examined, 87.6 % were positive for either Nematode and/or Cestode eggs. Anaerobic digestion of the sludge had little influence on the numbers of helminth eggs while conditioning with lime plus ferric chloride reduced the egg recovery. Helminth eggs were found in sludge samples stored for 1–2 or 3 years, but none were found in samples stored for 4 years or more. None of the Ascaris eggs tested were viable.
Out of the 57 sludge samples examined for virus, all the biological sludges contained enterovirus, while only 44 % of the digested sludge samples and 10 % of the semi-dehydrated and conditioned (lime plus ferric chloride) sludge samples were positive for enterovirus. No virus were found in stored sludge.
Epidemiological studies are necessary in order to determine any risks presented to public and animal health by the agricultural use of the sewage sludge.