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Biological drying as a sludge management option


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Biological drying offers an efficient, cost-effective alternative to traditional sludge dryers through microbe-generated heat. Volume and weight reductions lead to lower transportation and disposal tonnages.

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Biological drying as a sludge management option

  1. 1. Biological drying Exploiting the power of microbes to dry high-moisture materials
  2. 2. Biological drying relies on air flow and ...
  3. 3. HEAT
  4. 4. But not heat generated by electricity
  5. 5. or a fuel source
  6. 6. or even the sun.
  7. 7. Heat for biological drying is generated by microbes.
  8. 8. Here’s how it works:
  9. 9. During biodegradation, microbial feeding activity breaks molecular chains and generates heat.
  10. 10. As microbes feed, molecules continue to reduce in complexity until they become ...
  11. 11. simple compounds ... like H2O.
  12. 12. H2O, CO2 and heat are the byproducts of this biological activity.
  13. 13. The natural degradation process can be controlled and exploited for product manufacture (composting) or volume and weight reduction (drying).
  14. 14. How does drying differ from composting?
  15. 15. Both begin the same: 1. Wet material is blended with dry amendment to achieve specific moisture level, particle size, homogeneity, and porosity goals for the processing batch.
  16. 16. 2. The blend is placed in a processing bay.
  17. 17. 3. Sensors are placed in the admixture to relay information to a microprocessor.
  18. 18. 4. Doors are closed, and the computer takes over.
  19. 19. But instead of composting instructions, a drying program will be using a different set of processing parameters to control temperatures and air flow.
  20. 20. When the only processing goals are related to drying and not PFRP/VAR attainment or compost manufacture,
  21. 21. drying can be faster and volume reduction greater than with the typical composting process. RAW MATERIAL COMPOSTED DRIED
  22. 22. Advantages of biological drying • More cost-effective than other drying technologies • Dries through “free” heat generated during microbial feeding activity combined with aeration, not applied heat • Optional heat capture and/or electricity generation Reduces transportation, disposal tonnage
  23. 23. CAUTION Dried sludge is not the same as composted sludge. Composting breaks down waste until it isn’t waste anymore. Drying merely drives out water. Compost, when wet, smells like damp soil. But dried sludge may still generate unpleasant odors if rewetted. Therefore, general use of dried sludge by/near sensitive receptors is not recommended.
  24. 24. View more titles in the Talking Compost series at Production costs for this title were underwritten by McGill. Its use is permitted for educational purposes if presented in its entirety and without editing or other alteration. ©McGill Environmental Systems of N.C. Inc. Questions? Call McGill HQ at 919-362-1161 or use a contact form at