The Voice: Fall 2001

The Voice

Smits’ farm uses anaerobic manure digester to keep their community clean and protect the environment

Alumni spotlight

Sonya Jongsma Knauss

Putting in the manure digester will also benefit the Smits’ neighbors and community.     Nancy (Hoffman, ’87) Smits and her husband, Dan, are preparing to try out a unique form of manure stewardship. The Smits, who own the Double S Dairy near Waupun, Wisconsin, with Dan’s brother Steve, who attended Dordt in 1995, are building and installing an anaerobic manure digester, which will allow them to trap the methane produced by manure in order to generate electricity.
    Nancy works part-time as the bookkeeper for the farm’s operations, along with volunteering at Waupun Christian School where she used to teach. She says some of the questions that went into making the decision to build a manure digester were, “What can we do to make our farm a good place for us to live and a good place for our community? How can we keep it clean and how can we keep our water clean? What can we do to promote farming but also protect the environment?”
    According to Dan, manure digesters were around in the late 60s and 70s, but then seemed to disappear from the farming scene. He’s not sure why, but he thinks it makes sense to bring them back. “With the current focus on renewable energy, they're going to be something that people start using again,” he says.
    Ten miles northwest of Waupun, Wisconsin, the 620-cow Double S Dairy covers about 1500 acres of land, most of which is used to grow feed for the animals. This year, the Smits are taking on an expansion project that includes adding 300 cows, building a new milking parlor, and completing the manure digester—an airtight, municipal-grade wastewater processor.
    A manure digester is a big concrete pit that “digests” manure. Smits hired an engineer to design one for the farm. Manure goes into the pit, which measures 60 by 106 feet, and is kept at 100 degrees in an airtight environment for twenty-one days. While it sits, it creates gas. The gas is piped to a motor, and the motor runs a generator. Alliant Energy, the local utility company, is providing the motor and generator and doing upkeep on them.
    According to Irvan Possin, the dairy and livestock agent for Fond du Lac County in Wisconsin, naturally-occurring bacteria break down the manure. In an extension news column, he explains how plug-flow digesters—like that of the Double S Dairy—work.
    “The manure enters into a mixing tank before going into the digester and decomposes as it moves through. Hot pipes circulate hot water off the engine manifold to keep the temperature at 95-105,” he explains. The manure then forms a thick, sticky material called a plug, and passes through the digester in about twenty days. The methane is piped out.
    After the twenty-one days in the digester, the manure enters a separator. From there, the liquids are pumped to a manure lagoon, and the solids are dried. The Smits plan to use the dried manure for bedding instead of sand, and they hope to sell any dry manure they don't use to other farmers for bedding.
    “We sell methane to Alliant, and they make the electricity,” Dan explained. “They say they’ll be able to use the methane we produce to generate enough electricity for 133 homes,” Nancy says.
    The Smits haven’t finalized an energy contract with Alliant, but they estimate the sale of methane will only cover about forty percent of the cost of building and installing the digester and all its parts. The dairy estimates it will pump five million gallons of cow manure into the digester per year.
    The digester, if it works as planned, will create enough heat to heat the farm’s milking parlor and the shop and to dry the manure.
    “We use sand for bedding right now, and it’s great for the cows but it’s really hard to work with, settles out of your manure pit, and is hard on your equipment,” Dan says. “Dry manure isn’t hard on the equipment, and it’s good for the cows because sometimes bacteria can be found in the sand.”
    After the manure is heated, it is almost “pure.”
    “There's no e-coli—there is supposedly nothing that can grow in the dry compost,” Nancy says. “It's almost like it's pasteurized.”
    Manure used to just go to the manure lagoon and get spread on the land. As anyone who has lived in a rural area knows, this is what gives dairy farms their trademark odor. But that could change with the digester.
    “The manure is supposed to have ninety percent less odor after it goes through the digester and dryer,” Nancy says. Dan isn’t so sure about that figure, but he says it at least should have less odor.
    Dan doesn’t think the digester will be a big money-maker, but he thinks in time it will pay for itself. The farm will no longer have to spend $26,000 per year for sand for bedding, and their facilities will be heated for free. Some farmers who are building digesters have gotten grants, but he says they didn’t apply for one.
    The cement portion of the digester is complete, and the next step is to put the motor into a building and build some piping outside the digester. They hope to finish the project by early December.

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