When meat producer Packerland (now JBS) needed to reduce its solid waste disposal costs after the passage of the Clean Water Act, it turned to its former corporate engineer, Stephen Dvorak.
So in 1985, Dvorak helped the company build the first anaerobic digester in Wisconsin, which won a governor’s award and is still working today. Another law passed in 1999 that held farmers liable for farm odors, providing the catalyst for an idea that would inspire Dvorak to launch DVO, Inc. The Chilton-based company focuses solely on building digesters, said Melissa VanOrnem, who is Dvorak’s daughter and vice president of marketing for DVO.
“Dad started to think back to Packerland again on what he liked and didn’t like about that system,” she said. “He spent a lot of years doing research and development and he came up with our patented mixed plug flow system.”
“There isn’t one like it anywhere in the world,” VanOrnem said.
Traditionally, digesters have fallen into two categories. In a “plug flow” digester system, the new waste material pushes the older material forward. The benefit of these digesters is knowing the retention time of the waste and being able to destroy harmful bacteria.
“Mixed” digesters, commonly a European technology that is also being used in the states, are generally upright tanks that have a propeller or auger inside to mix the waste solids. The benefit is having the waste stay in suspension without settling issues, but you don’t have a guaranteed retention time, VanOrnem said.
“Our digester is unique because we are mixing a plug flow, and nobody else was doing that,” she said. DVO digesters combine the benefits of a guaranteed retention time while mixing the waste with the naturally occurring biogas in the digester, avoiding the settling issues, “and we get the best of both worlds.”
Josh Meissner of Norm-E-Lane Farm in the central Wisconsin town of Chili installed a digester in 2007.
“We were interested in separating solids for bedding,” Meissner said. “The digester makes a better bedding product, and we just thought it was a new technology that was going to take hold in the industry.”
In addition to the benefit of bedding, the digester at Norm-E-Lane also reduces odor on the 2,400-cow farm and produces about 600 kilowatts of power that’s sold to Dairyland Power Cooperative. The farm would consume about two-thirds of that energy in the summer months.
Meissner said he was attracted to the simplicity of the DVO digester versus the above-ground tanks and covers that come with other types of digesters.
“They’ve just been really good to us,” he says. “They’ve always been here doing whatever they need to make the project work.”
DVO digesters not only process manure, but can also process excess produce and other food waste. Farms with DVO digesters have taken material from Wal-Mart Superstores and food production companies, such as cheesemakers.
“We’ve got digesters in Vermont that are taking in waste from Ben & Jerry’s Ice Cream,” VanOrnem said. “Which, whenever I say that, people always say ‘How could there be any waste?’”
The digesters produce three main byproducts:
- Biogas can produce electricity and also can be “scrubbed” of carbon dioxide and hydrogen sulfide to produce methane, which can be compressed into natural gas.
- Solids that are similar to peat moss and can be used for cattle bedding.
- Digested liquid that can be used as a safer alternative fertilizer to raw manure. DVO also can pull more phosphorus and nitrogen out of the processed liquid as needed.
DVO has installed digesters at dairies that range in size from 400 to 15,000 cows.
“We really design it for each farm,” VanOrnem said. “When they tell us how much waste they have, we size the vessel accordingly. We think that it can work on a wide range of farm sizes.”
While the size and cost vary, an average traditional digester with an engine for electrical production on a 1,000-cow farm might be installed for under $2 million. Considering all the benefit factors, farms might see a three- to seven-year ROI on the digesters.
DVO digesters also benefit local communities by hiring local contractors for installation, VanOrnem said. It’s also a renewable energy source that doesn’t have the same challenges of solar and wind.
“Biodigesters really solve a lot of societal and environmental problems,” she said. “I just think if more people are aware (of the technology) there would be more interest and more demand for biodigesters.”