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UW – Oshkosh paves way for small-scale digester projects

PD Editor Karen Lee Published on 20 November 2013

This one is located on Allen Farms, six miles outside of Oshkosh, Wisconsin.

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Last year, the University of Wisconsin – Oshkosh commissioned its second anaerobic digester.

Click here or on the image at right to download a PDF of this image.

Dubbed “Titan 55,” the small-scale digester manufactured by BioFerm Energy Systems, is a plug-flow wet fermentation system with an electrical capacity of 55 kilowatts.

Together with UW–Oshkosh, BioFerm hopes this digester will blaze the trail for similar projects across the country.

“This project represents one more way for our students, faculty, university to further develop high-impact environmental studies, learning and research opportunities, champion environmentally friendly agricultural practices in the community and strengthen our regional identity as a rural renewable energy beacon for Wisconsin and the U.S.,” UW – Oshkosh Chancellor Richard Wells says.

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He continues, “For dairy farmers and the dairy industry, the technology shows incredible promise to reduce operational energy costs, and the potential, future regional manufacturing of these smaller biodigester units offer tremendous potential for job growth in the state.”

At Allen Farms, one of the biggest benefits the dairy producer has found is in using the digestate as fertilizer. Prior to the digester, he hauled manure directly to the field from the barn or storage pile, explains Steven Sell, application engineer for BioFerm. Now, the dairy producer can agitate the lagoon for a more even distribution of nutrients.

The parlor water and solid bedding are digested together and come out of the digester as a uniform pumpable liquid at 10 to 12 percent solids content.

This results in less time and labor when it comes to loading the manure. Instead of bucketing the stockpiled solid manure, this producer just has to hook up the pump.

He was able to use some post-digested manure on a few of his crops this year and noticed increased yields for both corn silage and ryegrass, Sell reports.

Although he hasn’t experienced the full benefit from multiple cropping years, he was able to notice the advantage this digested fertilizer, which is more readily available for plant uptake.

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The digester helps complete the circle at the farm, Sell says. The farm is now able to feed the energy it creates back into the dairy without having to bring in extra energy. Meanwhile, it is not losing the fertilizer value. “It is closing the loop on the whole business,” he says.

With the exception of loading manure into the digester, all functions related to operation and maintenance of the system are carried out by the university.

In conjunction with its dry fermentation digester on campus, the university handles the negotiation and contracts for all additional substrates.

When possible, it delegates various substrates to this project, which is currently taking in a lactose byproduct and restaurant waste grease.

All electricity produced is sold to Wisconsin Public Service under the blended advanced renewable tariffs (ART) rate of $0.0807 per kilowatt-hour. UW – Oshkosh and Allen Farms appropriately share the revenue, which allows Allen Farms to offset electricity consumption costs per year and provides a higher return for the university.

This particular digester unit was purchased from Germany. The university was able to obtain two grants for the project, of which a portion was used to help offset the expense of shipping.

Because this digester is ideally sized for 100-cow to 400-cow farms, and there are a number of these in the U.S., BioFerm is planning to open a manufacturing site in Wisconsin to help reduce the cost.

It is also considering the option of a lease agreement to make the option more appealing for farms that lack a large amount of investment capital. PD

Karen Lee
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