INACTIVATION OF VIRUSES, PATHOGENIC BACTERIA AND
PARASITES IN THE AUTOHEATED AEROBIC THERMOPHILIC
DIGESTION OF SEWAGE SLUDGES
Randolph M. Kabrick, Research Support Specialist
William J. Jewell, Associate Professor
Department of Agricultural Engineering
Cornell University
Ithaca, New York 14853
B. Vincent Salotto, Project Officer
Ultimate Disposal Section
Donald Berman, Virologist
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
INTRODUCTION
The traditional public health focus of wastewater treatment has been on the liquid
fraction of the wastewater because it is this portion that is returned to our rivers, lakes
and other waterways, which must be safeguarded against pollution. The relatively low
incidence of waterborne disease outbreaks among first world countries reflects the abdity
to satisfactorily treat wastewater by biological, chemical and physical processes and subsequently disinfect the liquid portion, e.g., with halogen compounds, prior to returning
that liquid portion to the environment. However, as we know, accepted treatment processes for wastewater generate a large amount of sludge. At present, the sludge production
rate in the United States is estimated to be 4.5 billion dry kdograms per year. These
sludges should be disposed of or utilized in some manner which would pose minimum
health threat and would be cost effective. Traditionally, little emphasis has been placed
on the ultimate disposal of these wastewater sludges with the majority of sludge buried,
burned or dumped at sea.
The Environmental Protection Agency has put forth guidelines which suggest that
sewage sludges and other waste organics be used for beneficial purposes when such practices are safe and cost-effective. At this time, land application of sludges appears most
favorable since sludges could provide the required plant nutrients for millions of acres
of cropland.   However, present sludge management technology often cannot guarantee
public health protection or cost effective solutions. This chapter details the pasteurization
ability of the autothermal aerobic digestion process in contrast to that achieved in
conventional anaerobic digestion systems. An earlier paper discussed the details of the
air aerated autoheated system [ 1 ]. This system was shown to be capable of delivering a
stabilized, pasteurized sewage sludge at costs comparable to present sludge processing
systems. The results presented in this chapter are based on the fate of the background
levels of various pathogens in sludge when treated by an aerobic thermophdic system
and a conventional mesophdic anaerobic digestion system.
BACKGROUND
Autoheated Aerobic Digestion
The autoheating phenomenon commonly observed in composting of solids has not
been applied to liquid organic slurries untd recently. Because of the small amount of
771