Many people consider manure to be a liability, but anaerobic
(or methane) digesters convert this manure into electricity, fertilizer and
bedding, creating value-added products for the community.
Liquid manure (slurry) is trucked in from a few dairies and
emptied into a pit. Like livestock, the digester must be fed continuously.
There is a sensor on the digester that indicates when the digester needs more
manure and substrate, and then it flows from the pit it is emptied into. The
manure and substrate are called feedstock. This particular digester uses dairy
manure and grease, along with a few other substrates.
The view from the top of the digester looking out on the building that houses the generators and the solids (far left) |
The manure and substrate mixture stays in the digester for
approximately 22 days. After that point, the methane is pumped off through
pipes and the solids collected. The solids are used as bedding on dairy farms
(and probably other types of farms, too) and can be used as fertilizer for
greenhouses.
The yellow pipes here are for the gas and the green are water |
Excess heat from the digester is used to heat the water in this large stainless steel tank |
If methane is not used, it cannot be stored unless it is
compressed into compressed natural gas (CNG). Since this digester does not
produce CNG (that I know of), they must flare any excess. This just looks like
a flame.
The digester produces one megawatt of electricity every kW
hour, enough to power 800-1,000 homes.
This digester is different from the others I’ve seen in that
it is more of a co-op digester that brings in manure from several dairies. Most
of the digesters I’ve seen and heard about are on a farm and utilize the manure
from that farm, along with another substrate like produce, ice cream, grease or
many other substrates.
The roof of the digester. The yellow pipe you see if where methane leaves the digester. |
At the end of the process, the methane is extracted, solids
removed and any liquid remaining is returned to the dairies to use as
fertilizer on the fields, reducing the need for chemical fertilizer.
It amazes me how a place with so much manure really doesn’t
smell like manure.
The building that houses the generator |
Technology use on farms continues to increase the efficiency
of today’s livestock operations and this is just another way to utilize the
manure to produce something useful for the community. As the number of farms
continues to decrease and some farmers approaching retirement age without
another generation to take over the farm exit the farming business, we will
need to use more technology to continue producing more with less. Technology is
a good thing. It helps us take BETTER care of our cows, our land and also the
community.
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