130 Organic waste recycling: technology and management
shown in Table 3.6, while the relationships between time and temperature that
cause pathogen inactivation as shown in Figure 3.1 are useful information to
determine the required composting period.
The microbiological quality guidelines shown in Table 2.27 and 2.28 should
be strictly observed when the composted products are to be used as fertilizers in
agricultural or aquacultural activities, respectively.
Table 3.5 Examples of pathogens found in, or generated during, composting of sewage
slidge, together with human diseases associated with these pathogens (U.S. EPA 1981)
Group Example Disease
Primary pathogens
Bacteria Salmonella enteritidis Salmonellosis (food
poisoning)
Protozoa Entamoeba histolytica Amoebic dysentery
(bloody diarrhea)
Helminths Ascaris lumbricoides Ascariasis (worm
infecting the intestine)
Viruses Hepatitis virus Infectious hepatitis
(jaundice)
Secondary pathogens
Fungi Aspergillus fumigatus Aspergillosis (growth in
lungs and other organs)
Actinomycetes Micromonospora spp. Farmer's lung (allergic
responses in lung tissue)3.7.2 Health risks from secondary pathogens
The contact or inhalation of air, containing a high density of spores of secondary
pathogens can cause health hazards to the compost workers and users. An
epidemiological study was conducted on compost workers at 9 sludge composting
plants in USA to evaluate the associated potential health hazard (Clark et al. 1984).
The results summarized in Table 3.7 indicate a higher health risk for the compost
workers than for the control groups not involved in compost activities, nose and
throat cultures positive for Aspergillus fumigatus were more common for these
compost workers than for others. Since Aspergillus fumigatus can cause serious
infections to lungs and other human organs, proper care must be taken to avoid the
uptake of these spores.
The growth of Aspergillus fumigatus in composting may be controllable
through moisture control management practice (Finstein et al. 1980) because
fungi tend to thrive in material that is slightly too dry for profuse bacterial
growth (Millner et al. 1977). However, routine monitoring for the presence of