Wednesday, July 2, 2014

Powering communities with cow manure

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.

They installed a digester about half a mile down the road from our farm a year or two ago, so I decided to go check it out.

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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