106
Discussion
inconsistent with the observation that the mixing characteristics of the anaerobic digesters used here
precluded a really significant virus inactivation.
Summary
Virus inactivation in anaerobic sewage sludge digesters is at least a function of and may be
primarily caused by the temperatures and retention times used. The commonly used completely mixed
primary digesters followed by unmixed secondary digesters do not provide a sufficiently long
detention time for significant virus inactivation. As shown by this discussion and Dr. Palfi's data,
digested sewage sludges must be considered as material containing pathogenic viruses.
1,000
(Temp)(Time) °C x Days
Fig. 1 Survival of Poliovirus Type I with time and temperature.
L. Coin, France.
For a century raw sewage and digested sludge from Paris had been treated on land. Vegetables
grown on such land had been examined by the Laboratoire d'Hygiene, Paris, and found to be free