Simplot Canada is constructing
a new french fry plant just an
hour's drive west of Winnipeg,
Manitoba. An important element
of such potato processing plants
is waste treatment. Disposing of the potato
solids as a by-product for animal
feed was not the usual obvious choice
at this location due to a lack of cattle
feedlots in the vicinity. Energy considerations
were also important.
Because of these and other factors,
Simplot decided to release the peel
waste into the drains.
After fine-screening to remove the
skins, the process wastewater is treated
in a low-rate anaerobic reactor. The mud,
or silt, is removed in a separate mud
clarifier. The fatty water stream is subjected
to fat removal prior to joining the
main process stream en route to the
anaerobic digester.
This is believed to be the first time
in 20 years that a large french fry plant
has chosen to anaerobically digest all the
solids after screening the process stream
containing peel waste. ADI proposed
the same arrangement for other potato
plants 20 to 25 years ago, and it currently
has active proposals for the same scenario
at a couple of other potato plants.
ADI Systems was the successful bidder
on this project, with its proprietary
BVF® digester. This is the third
Simplot-owned plant to install this type
of reactor; however, the other two plants
both have peel segregation (animal feed)
and primary clarification upstream of the
digester. This will be the first plant of
the three to burn the generated biogas,
from day one, in its process boiler, displacing
natural gas.
The 20 x 106USgal (77,000 m3) digester
is designed to treat a maximum
monthly flow and load of 9,900 m3/d,
63,000 kg/d COD, and 18,000 kg/d suspended
solids. Assuming 90 percent
COD removal, 130 x 106 Btu/d of biogas
energy will be produced, or enough to
raise 5,400 lb/h (59 tonnes/d) of steam
in the process boiler.
The anaerobic effluent will be sweetened
(oxidation of sulfides) in an aeration
tank equipped with subsurface aeration
equipment. Sweetened effluent will
be pumped through a 10 km (6 mi) force
main to the city’s secondary plant for
polishing prior to discharge to the
Assiniboine River.
ADI Systems is under contract to provide
the anaerobic digester and aeration
tank on a design-build basis. Donohue®
& Associates was the process engineering
consultant to J R Simplot of Boise,
Idaho, the parent company of Simplot
Canada. Financial assistance was provided
by both local and provincial governments.
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