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Newsletter and Technical Publications
<Municipal Solid Waste Management>

Sound Practices
Special wastes

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 household washwater;
  • 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.

 

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