Could hog manure be an environmentally friendly avenue for ethanol production? Meet some people who think the answer to that question is "yes."
By Holly Jessen | July 15, 2010
Of all the possible feedstocks for an ethanol plant, hog manure has to be one of the most aromatic. A Canadian hog farmer and a group of researchers in North Carolina are approaching hog waste from different anglesone targeting recycled water and the other looking directly at the cellulose fraction. What these projects have in common is converting what comes out of the posterior of a pig into ethanol.

Clean Water from Waste
Will Kingma, owner of Kingdom Farms, thinks that ethanolas part of a bioenergy clusteris the answer for his hog operation near Bentley, Alberta. Kingma envisions a future where his hog operation works synergistically with four elements: a water recycling system, an ethanol plant, ethanol coproducts for feed and biodigestion for power generation.

Kingma's 1,800 sows produce about 35,000 to 40,000 pigs a year that, in turn, produce about 18 million gallons of manure. After getting complaints from the citizens of nearby Bentley, Kingma started looking for ways to reduce the odor. "We wanted to be able to produce hogs in a neighborly fashion," Kingma tells EPM. He was also looking for ways to bolster his business financially, due to the poor economics of hog farming.

After several years of searching, Kingma is partway to his goal. The first step was installing a Livestock Water Recycling system, recovering 70 percent of the liquid in hog manure as potable water. The process reduces the original manure volume by 85 percent, resulting in a small amount of solids and an ammonium-rich fertilizer that can be sold or used on the farm. Its planned processing speed is 30 gallons of manure a minute, said Ross Thurston, president of LWR, the Calgary, Alberta, company that manufactures the system.

This is the first system installed on a hog farm and several more are in the works, he says. The company has units that can handle varying amounts, from 10 million gallons of manure yearly, to two combined units processing up to 75 million. Kingma estimates the savings alone from reducing the amount of material to be trucked away amounts to about $8 a head. LWR breaks it down this way: The current cost of handling and transporting manure ranges from 90 cents to $1.50 a gallon while the LWR system costs about 25 to 40 cents per gallon of manure to operate. "Their pay-out will be less than two years," Thurston says.

The next step for Kingdom Farms is a wheat-to-ethanol project. The 6.6 MMgy proposed ethanol plant is currently in the engineering, permitting and financing stage, with a projected construction start in the spring or fall of 2011, Kingma says. The plan is for recycled water from the LWR system to supply about 50 percent of the ethanol plant's water needs. The ethanol plant will produce wet distillers grains (WDG), half of which will be pumped directly to the barns and fed to the hogs on site. Currently, Kingdom Farms purchases WDG from the Permolex International ethanol plant located about half an hour away. Producing WDG on site will save the hog operation another $10 to $12 a head.

The remaining WDG will go into a biodigester to produce methane gas for electrical generation. It would produce more than enough power for on-farm use and may also produce enough electricity to be sold to the grid, Kingma says. In addition, because there's no need to dry the distillers grains, the plant won't need centrifuges or dryers, which should save about one-third of the capital costs.

Zeroing in on Cellulose
Jeffrey Macdonald teaches biomedical engineering at the University of North Carolina. He's also CEO of BioRxn, a startup company working to develop a cost-effective way to turn manure into electric power and ethanol while reducing odor. Macdonald got the idea when driving through North Carolina, the state ranked second behind Iowa for hog production. Two North Carolina counties, Duplin and Sampson, have a population of about 50,000 each, more than 2 million hogs each and a big odor issue.

All the volatile aromatics in the air got him thinking. Why not take that problem and turn it into methane, CO2, recycled water and ethanol? Hogs, once they hit 200 pounds, excrete an amazing 2.2 gallons of waste a day, Macdonald says. That's nearly 10 million gallons of manure daily from the more than 4 million hogs in Duplin and Sampson counties alone. Macdonald calculates North Carolina hogs are currently wasting $900 million a year in unutilized power. He calculates that BioRxn technology could convert the waste from 1,000 hogs to 20 kilowatts of energy and receive a premium of 18 cents per kilowatt from a renewable energy credit.

At a typical hog operation in North Carolina, hog manure is moved from barn pits to lagoons and then spread over fields as fertilizer. The state has limits on how much manure can be spread as fertilizer, however, and operators aren't allowed to create any more lagoons than the ones already in use. Macdonald's idea is to put a bioreactor between the hog barn and the lagoon, remove gasses and cellulose and send recycled water to the lagoon. "We don't want to get rid of the lagoon, per se, we'll just get rid of the stink," he says. Another positive will be that by reducing the nutrient load in the lagoons, hog operations could potentially expand since the land limitation for spreading waste due to overloading of nutrients would be mitigated.

Macdonald and Andrey Tikunov designed a bioreactor using tubes filled with water and bacteria for separation and anaerobic digestion of the hog manure. The methane produced could be used for electric generation for use on the farm or to be sold to the grid.

To produce ethanol from hog waste, Macdonald says one avenue could be simple fermentation of the sugar fraction at the start of the process. In addition, the team has also submitted a grant proposal to research the use of acetogenic bacteria in the final stage of the BioRxn process to produce ethanol.

The next step in the bioreactor design may be to separate the cellulosic fraction to be sold as feedstock to an ethanol plant. Hog feed is, after all, 80 percent corn, Macdonald says. Swine are not ruminates like cows, and instead of digesting cellulose, they concentrate it. So, the cellulose would be a high value feedstock, and unlike wood chips, it would be preprocessed and soluble. "What the market needs will dictate the direction that we take it," says Michael Van Hoy, scientific and business advisor for BioRxn.

The intriguing thing about the BioRxn bioreactor is that as a gas lift multi-phase bioreactor it should be more efficient than stirred bioreactors. Van Hoy compares a single-phase stirred tank to human digestionif it was done using only the mouth. The multi-phase bioreactor, however, is like using the whole human digestive system, the mouth, stomach and intestines. "We're designed that way for a reason," he says. "And for similar reasons, our multi-phase bioreactors should be more efficient than a single phase stirred bioreactor."

At this point, Kingma's idea of using water recycled from hog manure for ethanol production is the closest to becoming a reality. BioRxn's project is in the very early stages of development and the company is still working to scale up the bioreactor to handle about 20,000 gallons of hog waste a day and, possibly, isolate and degrade the cellulose into cellulosic ethanol, Macdonald says. If successful, these projects could turn the sour smell of hog manure into the sweet smell of opportunity. EP

Holly Jessen is associate editor of Ethanol Producer Magazine. Reach her at (701) 738-4946 or hjessen@bbiinternational.com.