Newsletter and Technical Publications
<Municipal Solid Waste Management>
1.7.8 Sewage sludge, septage, and slaughterhouse wastes
Sewage sludges are generated in sewage treatment
plants. Septage, on the other hand, is the material pumped from septic tanks.
Both of these materials contain large quantities of pathogenic organisms and
they often contain chemical contaminants, as well. They therefore require proper
treatment and disposal.
Slaughterhouse wastes can be used to produce ingredients in the manufacture
of fertilizer, animal feed, and glues. The traditional methods of sun-drying,
breaking up bones manually, composting in pits (sometimes with the addition of
household organics), and steam digestion carry various health risks, and cannot
be considered a sound practice.
Small-scale aerobic composting of animal wastes, including manures, hide
scrapings, and tannery and slaughterhouse wastes can also produce fertilizers,
but carries some risks in terms of spreading pathogens. All of these activities
generate leachate and associated bad odors, and are typically associated with
poor working conditions and risks to worker health, but may be profitable and
provide subsistence income. Sound practice could involve introducing technical
and health improvements, rather than eliminating the activities themselves.
|Sound practices for reducing and handling sewage sludge and septage
- preventing large volumes of sludge, through separation of
sewers and storm drainage systems;
- minimization of reliance on centralized sewage systems,
through the installation of on-site treatment of human waste and
- land application,but only when very frequent sludge
testing shows that metal content is very low, and when the
administering authority has the resources and commitment to maintain
high standards for such testing. In practice, this will mean that
in many situations the safety of land application is questionable.
- treatment such as drying, liming, composting, or
co-composting with yard waste or organics, followed by land
application, which is designed to return the organic matter in sludge
to the land. As above, however, contaminants in sludge can make this
practice inadvisable for farmland.
- drying it and disposing of it in landfills. It is important
to note that sludges should be dried before entering a landfill in
order to avoid generating large volumes of leachate.