Lessons Learned from this Project |
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Food Waste
Anaerobic digester demonstration
illustrating environmental benefits
Although the food waste brings in
additional solids to the digestion system fewer solids are in the effluent than
when just manure is digested. The extra energy of the food waste apparently makes
it possible for additional solids destruction. Solids were broken down in the
effluent storage as well. The existing manure storage was about one half full of
manure solids when digested effluent was introduced. After two years of operation,
the solids in the storage are almost all gone without excessive agitation.
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Food Waste
Anaerobic digester demonstration
illustrating environmental benefits
The food waste is high in energy having
three times the gas production per unit of mass than manure, yet the nutrient content
is comparable to manure so imported nutrients are kept low. Not all farms can take
advantage of this. Only farms that have a land base that can accept the extra nutrients
should consider this option.
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Food Waste
Anaerobic digester demonstration illustrating
environmental benefits
Gas handling pipes, flares and enterprises for energy use need
to be used for the additional production that a food waste system will require. Pre-planning
and analysis of potential food waste should be done to estimate the gas production and the
size of the utilization equipment.
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Food Waste
Anaerobic digester demonstration illustrating
environmental benefits
Accepting food waste is highly profitable. The tipping fees
make the manure treatment system a profit center for the farm. This is a win-win-win
situation. The farm gets a payment to accept the food waste and the extra energy as the
volatile solids are converted to methane, the food company has an environmentally
responsible and relatively cheap way to get rid of their waste product and the nutrients
from the food waste are recycled back to the land while green energy is produced.
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Heat
Anaerobic digester demonstration illustrating
environmental benefits
The waste heat given off by the engine generator is significant.
Utilizing the coolant to heat the influent and maintain the digester temperature
and using it for heat exchangers for hot water in the calf barn and milking parlor
still requires a radiator to dissipate extra heat. Even in the winter the un-insulated
engine building is very warm. This makes a very good heated shop and should be used for
that function.
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Mixed Digestion
Anaerobic digester demonstration
illustrating environmental benefits
The mixed digester performs well and offers
flexibility in operation accepting various consistencies of manure and food waste mixtures.
By mixing the influent into the total volume of the digester, the biomass that has been
built up in the digester can attack all the new feed. Even though some of the influent
goes out of the digester the first day, the total volatile solids reduction is significant
and the volatile acids (indicators for odor production) are low.
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System Design
Anaerobic digester demonstration
illustrating environmental benefits
The design of the anaerobic digestion system
including manure handling, gas collection, gas utilization, and digester heating should not
just be designed by each individual component but designed as a system.
This site experienced a beam failure due to lateral loads that were not anticipated
by the concrete designer. If the concrete design had been better integrated with the
rest of the project they may have realized that lateral loads could develop.
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