II.
UPEI Department of Engineering
550 University Avenue
Charlottetown
PEI C1A 4P3
Page
18
of 55
Major System Components
The main components of a small digester system are:
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Manure and feedstock collection
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Digester Tank and Heating system
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Biogas cleaning and combustion
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Electricity generation and distribution
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Digestate storage and field application
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Process monitoring, control, and safety systems
Manure and Feedstock Collection
Two of the example PEI dairy farms use scraped manure collection systems that gather raw
manure plus straw bedding twice daily. The scrape chain moves raw manure into a pit where a
piston pump transfers the manure through a buried pipeline approximately 50-100m to the
manure storage barn. The new site for Pleasant Valley farms uses a skid-steer to twice daily
move manure to the storage pit. Any practical biogas plant will need to be designed to work
with the existing solid manure collection system in order to keep retrofit costs low.
A liquid
manure system would require substantially different digester designs.
It is most economical to use the existing manure collection system entirely unmodified. This
includes the scrape chain system, the piston pump, and possibly the pipe that carries the manure
to the storage building. The question is whether the contents of the collection system are suitable
for digestion. Given that in both example dairy farms this is relatively fresh manure, a regular
amount of straw bedding, and perhaps a small amount of water, this doesn’t seem to be a
problem. It is worth noting how well-matched a plug flow digester is to this type of system.
While other types of manure digesters can provide greater yield and shorter residence time, they
would all require significant changes to the manure handling systems.
