Manure Power

By Sally Colby

Although the use of biogas from an on-farm methane digester is no longer considered breakthrough technology, installing a digester to convert dairy, hog or poultry waste to useable energy is still a pricey proposition. Most digesters are on large farms, and the farm owner's investment to install and get systems up and running is sizeable. However, it's a different story in Europe.

Cayuga County's methane digester will operate on manure from three local dairy farms, brown restaurant grease and woody biomass. The digester will produce ample electrical power for the county complex, which includes a prison, public safety building, nursing home, natural resources building and several barns and shops on a 3-acre campus.
Photos by Sally Colby.

Some European villages, including Jühnde in the northern German state of Saxony, have built "community," or centralized, digesters. Rather than running on inputs from a single-farm, centralized digesters rely on several local farms for manure and other biomass inputs such as crops and wood chips. In turn, the village is supplied with an economical source of renewable energy.

Jenny Pronto, research support specialist in the biological and environmental engineering department at Cornell University, says that in the U.S. digesters are found mostly on large dairy, hog and poultry operations. "Economically, it makes more sense for a larger farm," she said. "Technically, it can be done on a smaller farm, but farmers are less likely to have the capital for such a project. However, an opportunity for smaller farms is a centralized digester."

Pronto says that the town of Lowville, N.Y., was interested in constructing a centralized, or community, digester. The town began the process with a feasibility study to determine the goals and potential outcomes. Community goals included continued economic growth, limiting odor from manure and reducing the environmental footprint. Goals for the region's dairy producers included greater flexibility in manure handling and nutrient management, odor reduction from stored manure, and a potentially greater number of animals per unit of land with less environmental risk. The main outcome for local industry would be access to sustainable energy at lower costs.

The Lowville digester would be an upright tank style, similar to digesters commonly seen in Germany and Denmark. In addition to manure, the Lowville digester would accept nonfarm biomass such as whey, food waste, post-digested sludge and glycerin. The group held a series of town hall meetings to explain the digester and address concerns.

The electrical room at the Cayuga County methane digester facility is computer-operated.
"We showed slides of the digester in Jühnde, Germany, and told them how it was working there," said Pronto. "Lowville is a dairy community, and we thought that it would be well-received." The digester would be constructed on the same property as the sewage treatment plant, but there was significant concern about increased truck traffic in the area. Pronto added that because community digesters aren't yet common in the U.S., people tend to see them as risky. For now, the Lowville project is on hold, but another New York project has finally come to fruition.

"We've been working at it for six years," said Ron Podolak, referring to the community digester initiated by the Cayuga County, N.Y., Soil and Water Conservation District (SWCD) in the town of Sennett. Podolak is the executive director of the Cayuga County SWCD and has been an integral part of the project since its inception. "We have everything in place, and we're ready to start the commissioning phase," he said.

The goal of the SWCD was relatively simple: construct an anaerobic digester that would convert manure and other feedstock to energy. However, the project process is anything but simple. After completing feasibility studies, the team working on the project has had to select and plan for the appropriate genset (a power generation system located close to the end user), digester tank, storage facilities, gas lines, high-voltage lines and other supporting structures. Then the critical question: What will feed the digester?

Farms, along with their livestock, manure and feedstuffs, are literally in the backyards of nonfarm neighbors in German villages such as Jüehnde.

"We plan on taking in 32,000 gallons of manure per day," said Podolak, adding that the county currently has contracts with three dairies with a total head count of about 2,000 cows. "We'll pick up the raw manure at the farm and truck it to the digester. The manure will be digested, then go through separation to separate solids from liquids, and the liquid portion will be stored in a tank." Podolak describes the trucking process as a round- robin: raw manure will arrive from farms and go into a holding tank for storage. The same truck will be filled with post-digestion liquid effluent and return to the farm. At the farm, effluent will be pumped into a satellite storage unit for later use. The truck will then be filled again with raw manure at the farm to continue the cycle. Each of the farmers is responsible for providing a safe, clear area to load and must supply equipment (such as a tractor with sufficient hp) to load the tanker truck.

Community methane digesters, such as this one constructed in the village of Jüehnde, Germany, can solve manure storage and disposal problems as well as supply clean, renewable energy in the U.S.

Initial plans included the input of potato processing waste, but that company decided not to participate. "Now we'll be bringing in about 44 tons of brown grease that will come in in septic tank pump trucks," said Podolak. "The grease is gone after it goes through digestion, so none of that goes back to the farm."

The liquid effluent that will be returned to the farms will be much like a liquid fertilizer, with 90 percent available plant food. "The farms are really looking forward to that," said Podolak, "and so are their farm planners when they calculate how much they can save on fertilizer. It'll be pathogen-free and almost odorless." Podolak explained that the odor and phosphorus stay with the solids, which will be processed through a screw press and then go to a bedding recovery unit, which is basically a large composter. Although the bedding recovery unit isn't constructed yet, it's in the plan. Composted manure can then be returned to the farms for use as bedding or be converted to high-grade compost for landscape use.

Trucks will connect here to off-load manure.

In anticipation of questions from area residents during the early planning stages, public meetings were held. "People were concerned," said Podolak. "Communication and education are key. Everyone is satisfied with the answers they got. People understand exactly what's going on and that it won't smell like a 1,000-cow dairy because everything is contained." Podolak added that the public was even more convinced of the value of the project when they saw the numbers and calculations for energy savings in the public buildings of Sennett.

The methane digestion facility is housed on a county campus that includes the Cayuga County Jail and public safety building, the county nursing home, the natural resources building, and several barns and shops. "When we are up and running, we'll be producing .5 megawatt of power, which will be enough to power this entire campus," said Podolak. "We also have a power purchase agreement with New York State Electric and Gas, so when we have extra energy, it'll be sold back to the grid."

The genset for the system is a Jenbacher. "The design is based on German technology," said Podolak. "It's a hydraulic mix; a vessel-in-vessel." This type of digester has no internal moving parts, yet allows coprocessing of feedstocks of up to 15 percent solids. Hydraulic pressure in the inner vessel of the digester mixes the materials thoroughly, and because the digester doesn't include a stirring motor, expenses such as motor maintenance, cleaning and run time are eliminated. The hydraulic mix digester is flexible and can transition easily to various feedstocks.

The genset, an electrical generator located close to the end user, is a German- style Jenbacher unit.

Because the transportation of feedstock and return of digestion products is the most expensive part of the process, the three dairies supplying manure are all within a 10-mile radius of the plant. The group also anticipated possible expansion. Podolak says that the project is designed so that future additions will be easy. "We poured a concrete pad for another genset," he said. "We can add another silo and another genset and pretty much double our output. Additional farms are on a waiting list to supply manure. We looked ahead - the county might be constructing more buildings."

Additional revenue will come from carbon credits and tipping fees for the brown grease. Another bonus of the project is hot water. Podolak explains: "Hot water from the genset will be piped to the boiler at the public safety building. We can run the hot water line right into the boiler, and that will cut their natural gas bill by 50 percent per year, and that's a byproduct of running the generator. It doesn't get any better than that."

Podolak says that the brown grease will "boost the octane" of what's being produced. "We'll have so much power that the genset won't be able to keep up with the gas," he said. "The failsafe is that we flare it off - it's a safety factor." Another safety factor is the berm that encompasses the 3 acres containing the digestion plant. "We calculated the height of the berm so that if a catastrophe occurs, the total amount of manure, grease and other materials would be completely contained and not enter water." Podolak noted that the system is the first of its kind in the U.S., and that there will be no hazardous waste at the end of the process. "We have a state-of-the-art gas conditioner unit that is total biological," he said. "It will produce no hazardous waste and won't require expensive chemicals to clean up toxic portions."

The German company GBU designed the Cayuga County unit in conjunction with Seeler Engineering in Pittsford, N.Y. Podolak says that when it's time to actually flip the switch, GBU engineers will return to New York to make sure that the computer unit responsible for coordinating the process is online, and that all aspects of the unit are fully functional. Podolak says that the pumps and tanks have been tested with water, and the project is nearing the commissioning phase. This step involves priming the genset with natural gas, followed by introduction of biogas from manure.

Since its inception, the Cayuga County project has been stop and go due to funding, although the team has been diligent in seeking financial backing. "We'd go along so far and run out of money, and get started again and run out of money again," said Podolak. "Finally, we obtained a $6.2 million American Resource and Recovery Act grant through the New York State Environmental Facilities Corporation." An additional $3.5 million in federal and state grants and aid allowed the county to move ahead with the project. Podolak says that the project was more challenging and costly due to the "Buy American" requirement that required sourcing of materials from the U.S., but he's grateful for the financial assistance that made the project possible.

Although Podolak says that it sometimes seems like more than six years since the project started, it's good to see the results of the group's efforts. "It's a win-win for farmers and for everybody," he said.

The author is a frequent contributor and freelance writer who farms and raises Great Pyrenees in south-central Pennsylvania. Comment or question? Visit www.farmingforumsite.com and join in the discussions.