Biological drying relies on microbes and air flow to dry wet materials. During biodegradation, microbial activity breaks down molecules and generates heat. As microbes feed, molecules are reduced to simple compounds like water, carbon dioxide, and heat. This natural degradation process can be controlled and exploited for drying. Drying removes water from materials through microbial heat and aeration rather than applied heat. It reduces transportation costs compared to other drying methods but dried sludge may still generate odors if rewetted so general public use is not recommended.

1. Biological
drying
Exploiting the power of microbes
to dry high-moisture materials

2. Biological drying relies
on air flow and ...

3. HEAT

4. But not heat generated
by electricity

5. or a fuel source

6. or even the sun.

7. Heat for biological drying is
generated by microbes.

8. Here’s how
it works:

9. During biodegradation, microbial
feeding activity breaks molecular
chains and generates heat.

10. As microbes feed, molecules
continue to reduce in complexity
until they become ...

11. simple compounds ... like H2O.

12. H2O, CO2 and heat are the
byproducts of this biological
activity.

13. The natural degradation process
can be controlled and exploited
for product manufacture
(composting) or volume and
weight reduction (drying).

14. How does drying differ
from composting?

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. 2. The blend is placed
in a processing bay.

17. 3. Sensors are placed in the admixture to
relay information to a microprocessor.

18. 4. Doors
are closed,
and the
computer
takes over.

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. When the only processing goals are
related to drying and not PFRP/VAR
attainment or compost manufacture,

21. drying can be faster and volume
reduction greater than with the
typical composting process.
RAW MATERIAL
COMPOSTED
DRIED

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. 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. View more titles in the
Talking Compost series at
www.mcgillcompost.com
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Questions? Call McGill HQ at 919-362-1161 or use a contact form at www.mcgillcompost.com.