Remarkably few waste treatment technologies can be guaranteed to eliminate all
pathogenic organisms and agents even though solid waste, particularly sanitary solid
wastes and specified materials from animal slaughter and destruction, have been identified
as significant sources of various pathogens. Historically, most screening tests used
indicate the possible presence of pathogenic organisms and involve faecal indicator
bacteria, in spite of the fact that human pathogens include bacteria, yeasts, protozoa,
intestinal and other worms, flukes, viruses and prions and that individual elimination and
survival characteristics vary dramatically. Hygienisation processes involve two major
facets: the destruction or irreversible inactivation of all pathogens present and the
prevention of subsequent regrowth (recovery) of or reinfection with pathogens. As far
as biological hygienisation processes are concerned, the three major mechanisms
76 G. Hamer / Biotechnology Advances 22 (2003) 71–79
contributing to process efficacy are elevated temperatures, effective hydrolytic enzyme
production and high residual substrate affinities. Enhanced temperature clearly implies the
need to use thermophiles exhibiting high metabolic rates that permit autothermal
operation for process mediation. In heat inactivation, process temperature and time are
inversely linked as far as inactivation is concerned, so that guaranteed minimum process
residence times, with no possibilities of either material bypassing or cool spot (frequently
head space) segregation, are absolute requirements that depend on both process equipment
and operating system design