Power from the cows
Before anaerobic digestion gained much traction across the dairy industry, Allen Farms had already proven the merits of the manure-handling and power-generating technology.
“Our system was so much of a prototype in the beginning,” says Dave Allen, an Oshkosh, Wisconsin, dairy farmer. “Now that the bugs have been worked out, everything works well.”
Since 2012, Allen has worked in collaboration with the University of Wisconsin Oshkosh (UWO) and BIOFerm Energy Systems (biofermenergy.com) to purchase and set up the anaerobic digester on his 130-cow farm. The running of the digester now depends on Allen’s daily input of manure and other feedstocks, while UWO staff manage the technical aspects of the system.
Holistic efficiency is the hallmark of the digester’s role on the dairy farm. “We’re taking waste and collecting the methane from it,” Allen says. “From that, we’re generating electricity and heat. When it’s all said and done, we have an awesome fertilizer to put back on the land.”
The annual electrical output of the digester is enough “to provide power to about 50 average American homes,” says Brian Langolf, director of the UWO biogas program. “The digester’s 64-kilowatt combined heat and power unit can put out a maximum of 1,536 kilowatt-hours per day, or 560,640 kilowatt-hours per year. We are currently running at 80% to 90% of full output capacity. The electricity is sold to the local power utility.”
Besides managing the technical operations of the digester, UWO originally partnered in the project through funding contributions. Thus, UWO benefits from the sale of the electricity.
“We convert the biogas to electricity and sell it to the power company,” Langolf says. “The power company credits the electricity to the university, and in this way, our unique partnership with Allen Farms helps us achieve our sustainability goals on campus relating to reducing carbon emissions.”
Besides using the electricity from the farm’s digester, UWO also conducts research and educational activities for students at the facility.
Allen reaps the manure-management benefits, of course, along with the heat generated by the digester, which heats his 2,200-square-foot home and 45×54-foot shop.
The digester comprises two fermentation vessels with a combined capacity of 80,000 gallons. Allen loads the feeding hopper daily with manure scrapings, bedpack, and sometimes crop residuals from the farm and industrial food waste. The system processes nearly 6,000 tons per year of feedstock.
“We maintain the temperature at 100ºF. and add bacteria, and the bioproduct is methane gas,” Langolf says. The digester’s combined heat and power unit converts the methane to electricity and heat.
After this processing, the digested manure, or digestate, flows into an open lagoon, where it is stored for later applications to crop fields. “The digestate has less odor than raw manure, and its nutrients are more biologically available to plants than the nutrients in raw manure,” Langolf says.
Allen typically applies the digestate to the farm’s 700 acres of corn, soybeans, and alfalfa at a rate of 9,000 gallons per acre. “That amount of manure reduces the amount of purchased fertilizer we apply by quite a lot,” he says. “We do test our soils, and we follow a nutrient-management plan.”
If tests show that nitrogen is short for corn, for instance, he’ll supplement the digestate with 100 pounds per acre of urea. “On the other hand, if we’re taking a field out of alfalfa and we’ve applied 9,000 gallons per acre of digestate, the digestate and the alfalfa together supply the fertility needed to grow a crop of corn,” Allen says.
The crops supply all of the feed consumed by the cattle. “We always have an excess to sell, as well,” he says.
When relatively small-scale producers like Allen consider adopting anaerobic digestion technology, Langolf suggests that taking a holistic view of the system can give a big-picture look at the potential outcome.
“Don’t just look at potential production of electricity and heat,” he says. “Also look at the back end of the system. Look at its potential environmental benefits – for instance, how it reduces risk for possible contamination of groundwater by raw manure.”
Consider other nutrient-management benefits, as well, such as enhanced bioavailability of nutrients.
“Many of these benefits don’t always bring home a check to the farm,” Langolf says. “Where I’m seeing digesters being used most successfully is at farms where the operators view the value of the digester holistically.”
Nevertheless, purchase and setup costs of a digester system can be prohibitive to livestock operations, and the technicality of the systems’ oversight is burdensome. Offsetting these costs and challenges through energy sales from the farm is typically difficult because of present regulations within the energy industry.
“Barriers at some state and local levels exist for being able to cost effectively develop behind-the-meter options, net metering, and pipeline injection capabilities,” Langolf says.
This opens the door, he says, to organizations and companies partnering with farmers to bear the brunt of the investment and generate opportunities from digesters. (See story above.)
“I believe anaerobic digestion technology holds potential – both on its own and in combination with other technologies – to develop sustainable sources of energy,” he says.