Waste Not

Large and small
Minnesota dairy
farms use manure
digesters to produce
methane gas

By Stephen Thompson
Assistant Editor

n the heart of Minnesota’s dairy country, two dairy co-op members are looking to a future in which farm waste will be used to supplement America’s supply of electric power. Both are using technology that reduces pollution, greenhouse gas emissions and, hopefully, farm operation costs.

Methane digesters have been around for more than 100 years. Using the action of bacteria, they ferment manure and other organic waste to generate a mixture of CO2 and methane, called “biogas,” that can be burned to power electric generators. Municipal sewage-treatment plants around the country have used digesters for decades to help dispose of sewage sludge. They are also used to create power from farm wastes on a large scale in western Europe.

But in the United States, use of the technology on farms has yet to become significant. Dairy farmers Dennis Haubenschild and Jerry Jennissen hope to change that by running biogas generators that contribute significant amounts of power to the grid, and make money for their owners in the bargain.

True believer
Haubenschild is a true believer. “I know what happens when you’re nonsustainable,” he says. In 1953 when his father purchased the land Dennis farms today in Princeton, Minn., it had been completely exhausted by years of crops grown without replenishing the sandy soil. “The humus was just gone,” says Haubenschild. “It took years to get it productive again.”

His interest in sustainable farming has led him to try a number of unconventional measures on his 868- cow dairy farm, including solar heating a cow barn, water conservation and recycling. But the centerpiece of his conservation effort is an electric generator run by methane produced from his cows’ manure.

“A day’s worth of manure from 100 cows gives you the energy of one barrel of oil,” he says.

The methane is produced by a plugflow digester, a relatively low-tech method that uses a large, plastic-lined pit, covered by another plastic membrane. The manure and bedding are scraped from the floors of the cow barns and milking parlor twice a day and pumped into one end of the digester. As it flows the length of the digester, it ferments, releasing methane gas, which is scrubbed of harmful hydrogen sulfide and dried before being piped to an engine-driven generator.

Some of the waste heat from the methane-powered engine is used to keep the digester at optimum temperature; some warms the cow barns and milking parlor in cold weather, saving hundreds of gallons of fuel per month.

At the other end of the digester, after about 25 days, the fermented manure is run through a mechanical separator that squeezes out most of the moisture. The resulting fluid is piped into a lagoon; the solids, which are free of most pathogens due to the heat of the fermentation, are used as bedding for the cows.

It’s an elegantly simple, but effective, process. The fluid digestate is rich in plant nutrients, and — as a result of the digestion — is nearly odorless.

Standing next to the waste lagoon, the odor reduction benefit is instantly, and pleasantly, noticeable. Just a few feet away, one wouldn’t even know the lagoon is there, whereas the stench from conventional dairy manure lagoons often attracts the wrath of neighbors, municipalities and environmental authorities.

Environmentally friendly fluid
The digested fluid is environmentally benign; if it should get into local waterways due to runoff or floods, it shouldn’t kill fish and other aquatic life. And its 7.8 pH level means it can be spread on cropland without risk of burning crops.

Those are huge advantages at a time during which livestock operations and dairy producers are coming under increasing scrutiny by environmental groups and regulators over the smelly, toxic contents of their manure lagoons.

“We’ve doubled our output of alfalfa since we started using the digestate for fertilizer,” says Haubenschild. “We used to get three cuttings a year; now we get five. And it doesn’t smell when we spread it on the fields.”

The liquid is also easier to use. “It used to be that we’d spend two days just stirring the pit to get it to where we could use it for the fields. Now we get a little separation from snow-melt, but mostly we can just pump it out.”

The rest of the farm also reflects Haubenschild’s progressive attitude toward agriculture.

“Everything’s designed to increase efficiency and cow comfort,” he says. That’s reflected in the shed set aside for dry and gestating cows. The bedding is composted — mixed up twice a day with a chisel plow. The result is a fermentation process that keeps down odors and provides a comfortable, acceptably clean and dry substrate for the cows. Haubenschild even bales the plastic from his plastic feed storage bags for recycling. “I had a deal with my supplier for them to accept plastic back for recycling,” he shrugs. “That worked until the competition got down to one.”

Haubenschild’s farm is well-regarded by University of Minnesota agriculture professor Marcia Endres. “He’s a pioneer,” she says. She regularly brings classes on field trips to the farm to analyze and learn from the operation.

“We really appreciate his collaboration,” she says. In return, Haubenschild gets the benefit of fresh eyes.

Advancing fuel cell technology
The most ambitious of Haubenschild’s experiments in sustainability is the result of help from Deere & Co. and a partnership with the Dr. Philip Goodrich an associate professor of biosystems and engineering at the university. This effort involves a hydrogen fuel cell laboratory, set up to produce electric power from hydrogen extracted by the digester-produced methane.

Deere provided the grant to build the facility, with an eye towards possible future use of fuel cells in methanepowered farm equipment. The advantage of fuel cells is that they are more efficient at producing energy than generators driven by internal combustion engines.

Unfortunately, says Haubenschild, the money to operate the lab has dried up for the moment, leaving it idle.

Nevertheless, Haubenschild is optimistic about the potential of fuel cells. He points out that hightemperature designs now being developed, known as molten carbonate cells, can use methane gas directly, without first putting it through a catalytic cracker to separate the hydrogen.

And he sees another possible use for hydrogen extracted from biogas: ammonia production. Anhydrous ammonia for use as fertilizer is usually produced from hydrogen obtained from natural gas. Haubenschild thinks the production process is simple enough that small, decentralized production facilities could use hydrogen obtained from digester gas.

Power grid issues are complex
The big question, of course, is whether the digester pays its way through the sale of power. Haubenschild is on the grid of a local distribution cooperative, but selling the power he makes is complicated.

Minnesota law requires that electric utilities purchase some of their power from renewable sources — such as digesters and solar and wind generators. Amounts of power less than 40 kilowatts are purchased under netmetering agreements. Under such an agreement, power provided to the grid is paid for at the same rate as the utility charges the customer.

However, Haubenschild’s generator produces much more than that, so the rest is paid for at a much lower rate, not by the distribution co-op, but by the distribution co-op’s generation supplier.

Nevertheless, Haubenschild says the generator more than breaks even. He doesn’t elaborate, but his digester has been in operation for 10 years — long enough to work out the kinks.

Smaller farm also tries it
In contrast, Jerry Jennissen’s digester, installed in December, 2007, is just getting started. His farm, about 90 miles west of Haubenschild’s, near Brooten, Minn., is small in comparison; he currently milks 155 cows. But his digester and generator setup could be a prototype for other smaller dairy farms, if a few problems are worked out first.

Jennissen’s opportunity to build a digester came when The Minnesota Project, a nonprofit based in St. Paul, received a state grant through the Legislative-Citizen Commission on Minnesota Resources — a state government entity that recommends environmental and conservation projects for funding from Minnesota Lottery monies. The Project, in partnership with Genex Cooperative, a beef and dairy services co-op, was looking to develop a manure digester that would be feasible for use by small and medium dairies.

With the help of the Minnesota Milk Producers’ Association, Jennissen’s operation was chosen from a number of interested farmers to host the prototype, and a request for proposals resulted in the selection of a Utahbased company, Andigen, to supply the digester.

Andigen’s digester is a modern, vertical design called an Induced Blanket Reactor (IBR), and resembles a small silo attached to Jennissen’s cow barn. A far cry from the old style plugflow digester, it can process the manure from up to 200 cows in a cycle that takes about five days, instead of a month.

Because it only has to hold about five days’ worth of manure, it can be much smaller and less expensive. It’s easy to dismantle and sell if the farm shuts down, and it’s just as easy to add a second digester if the farm expands. And because it demands a slurry of about 8 percent solids, the design lends itself to the digestion of a wide range of substances, including pig manure, which give plug-flow digesters “indigestion” because of its high water content.

Computer allows remote operation
The digester and generator are monitored and controlled by computer, with an Internet connection making it possible for the co-op to run them remotely. The whole installation fits nicely in a new addition built onto Jennissen’s cow barn.

In addition to the state money, funds from USDA Natural Resources Conservation Service’s Environmental Quality Incentives Program, the North Fork Crow River Watershed District, Stearns Electric Association (the local electric cooperative), plus a considerable investment by Jennissen paid for the installation.

Jennissen says the original proposal called for the digester to be completely enclosed, but he chose instead that it be mostly exposed, to save money. About a quarter of the cylinder is attached to the barn structure, and Jennissen had the exposed portion insulated with three inches of plastic foam against the frigid winter winds that come roaring down from Canada. A coil of tubing around the tank’s midriff carries hot coolant from the generator engine when needed to keep the fermentation at the proper temperature.

Unfortunately, the setup has had its share of teething problems. When Rural Cooperatives visited, the generator was offline due to a failure of the methane engine — the second such failure in a few thousand hours of operation. Gas from the generator was being burned off in a flare.

For some reason, the engine, which is an automotive V-8 adapted for stationary use, was suffering accelerated cylinder and bearing wear. The cause was not clear. Was the operating temperature too low, the generator speed too low, or was hydrogen sulfide in the digester gas the problem? Rolly Meinke, Genex’s representative in charge of the digester project, came out to the farm to inspect the damage.

Unwilling to let such problems get in the way of the project, he arranged to replace the power plant with an industrial engine designed for natural gas, which runs at a higher operating temperature and speed.

Striving for greater efficiency
Meanwhile, Jennissen, Meinke and Joe Borgerding, an electrician who helped with the initial installation, are looking for ways to raise efficiency and increase cash flow. Borgerding, a trained auto mechanic who in his youth worked on drag racers, has become intensely interested in the project. He is working on developing an enginegenerator package he thinks will increase output and longevity — possibly doubling power output. Jennissen and Meinke are looking for ways to raise methane production by adding substances to the fermentation process. Associated Milk Producers Inc., a nearby marketing co-op, has agreed to supply waste whey to the project.

“We’ve already sent a sample to Andigen,” says Jennissen. “With 2,500 gallons a day we could double methane production.” Even restaurant grease will work. And Dennis Haubenschild is looking into the possibility of using waste alcohol from a nearby distillery as a fermentation booster.

Jennissen has also experimented with raising the fermentation temperature slightly, and is thinking of trying fermentation with thermophilic bacteria, instead of the mesophilic currently used. The conversion consists merely of raising the temperature of the tank from its current 105 to 125 degrees.

“I’m hoping maybe we can find a sweet spot that will produce more methane and less sulfur compounds,” he says. He’s also interested in current research to develop bacteria that reduce production of hydrogen sulfide.

The number of variables seems daunting, but both Jennissen and Meinke are convinced that with enough time and creative effort, the digester can become economically efficient. Jennissen’s electric distribution cooperative, Stearns Electric Co-op, has promised to buy any power produced over the 40-kilowatt level at 6.5 cents a kilowatt-hour. “Pretty much everyone I’ve dealt with has been very supportive,” Jennissen says.

Project manager optimistic
Ryan Stockwell, Clean Energy Program Manager for The Minnesota Project, is optimistic about the use of digesters on Minnesota farms, but says, “Changes need to be made.”

Part of the problem, he says, is the low cutoff for mandated net-metering power purchase agreements. Forty kilowatts isn’t much; even Jennissen’s small operation will produce substantially more when it’s up to speed. And the low rates offered by apparently reluctant power utilities for power provided in large amounts are a serious concern.

Next door, Iowa has mandated 500 kilowatt net-metering, while Pennsylvania requires power providers to accept up to three megawatts from non-residential customers. Stockwell says there are efforts in the state legislature to raise net metering requirements for solar- and windgenerated power, but currently not for digesters.

Stockwell thinks any pricing system should take into account benefits beyond the production of power. “We’re not putting a price on benefits like pathogen, odor, pollution and CO2 reduction,” he says. “The pricing doesn’t match the benefits.”

Then there’s the issue of establishing the technology. “We need to develop the institutional knowledge and the market,” Stockwell says. “It’s kind of a chicken-and-egg thing. You need an established market to get economies of scale, but the market’s not going to be there until you’ve developed your technology and you’ve got enough producers out there.”

Europe far ahead
Stockwell agrees with Haubenschild and Jennissen that the technology is much more established in western Europe. In Europe, digesters are commonly used to dispose of farm and food-processing waste.

More than 4,000 digesters in various sizes have been built in Germany alone. “We’re like teenagers compared to the Europeans,” Stockwell says. “They went through this 25 years ago — they learned from the oil embargo in the 1970s.”

At a minimum, Stockwell expects it to take four to five years before methane digesters on U.S. farms begin to take off. For other applications, such as waste from food processors, he thinks it may be 20 years before the technology is widely adopted.

His organization is trying to hurry things along by developing education and outreach programs to encourage grassroots support in Minnesota. It’s also working on a “best practices” digester handbook for farmers, using information gained from Haubenschild’s and Jennissen’s operations.

In any case, he thinks grass-roots support for the technology is building. “Every time Jerry and Dennis give a presentation about their systems, it’s standing room only,” he says. “People are definitely interested. Once we get the costs down and get pricing mechanisms in place, I think we’ll get a lot more investment.”



Bigger methane role for farmer co-ops?

Can farmer cooperatives play a larger role in promoting the recycling of manure into methane gas? In their new report (see page 39 for ordering information) USDA Ag Economists Carolyn Liebrand and Charles Ling raise possibilities that a cooperative approach could address the challenges of adoption of this technology through improved negotiating strength, technical assistance for digester design, installation and operation. They also suggest a possible role for co-ops in management and marketing services and/or financial guidance and assistance.

Cooperative efforts may allow milk producers to remain focused on milk production while lowering costs and/or increasing returns from energy and byproduct sales. The July- August issue of Rural Cooperatives will present a summary of the possible benefits from group efforts to adopt anaerobic digester technology.




















May/June Table of Contents