Manure Manager

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OMG, Google invests in North Carolina biogas-to-energy project on hog farm, FYI


The biogas generated by anaerobic digestion of hog manure on the Loyd Ray Farms operation is collected under this flexible dome. Contributed

In a world where a “like” or “dislike” thumb pointing up or down has immense control over public opinion, an endorsement by Google relating to the carbon credits generated by a project that uses biogas from hog manure to create electricity speaks volumes.

That’s the case with the $1.2 million green energy installation featuring anaerobic digestion of hog manure at Loyd Ray Farms in Yadkinville, N.C., about 25 miles west of Winston-Salem. Conceived and financed by Duke University and Duke Energy, Google helped pay for part of the university’s contribution toward the project in exchange for a portion of the carbon credits generated over the next five years, aimed at offsetting its own emissions.

“Google’s involvement adds a lot of visibility to the project because when they do something, everybody looks,” says Marc Deshusses, a professor of civil and environmental engineering at Duke University. He’s responsible for conducting a technical evaluation of the project, from overall performance to environmental impact. “The company is also very thorough in its search for high-quality carbon credits. Projects go through a rigorous evaluation process.”

Rather than liquid manure generated by the 8,640 hogs on Loyd Ray Farms being flushed into a storage lagoon and then land applied for disposal and fertilizer, about 196,000 gallons are processed weekly through the two-million-gallon anaerobic digester designed by environmental engineering firm Cavanaugh & Associates. The methane and carbon dioxide generated by the digester is diverted as fuel to a 65-kilowatt micro turbine-generator, which produces enough power on a 24/7 basis for five of the nine hog barns on the farm in addition to the environmental management system itself. The power generated by the project is the equivalent of the amount of power consumed annually by 35 homes. The liquid byproduct is collected in the existing 10.5 million gallon storage lagoon covering 4.8 acres, with a portion recycled through the hog operation as wash water and the remainder eventually land applied as organic fertilizer as well as used to irrigate cash crops. The plan is to clean out the solid sludge built up in the digester once a year and inject it as fertilizer.

The hog manure to biogas project broke ground in September 2010 and has been in operation since May 2011. Duke University and Duke Energy will share in the operating and maintenance cost of the project for 10 years.

Loyd Ray Farms owner Loyd Bryant says the farm benefits many ways. First, the power supplied by the micro turbine-generator has cut the farm’s power bill by $300 to $400 per month. Second, the reduced nitrogen content in the treated wastewater versus raw manure will allow the farm to use it as fertilizer on cash crops such as corn, wheat and beans instead of just hay on the farm’s 154 acres. State regulations do not allow application of raw manure on any crop other than hay at the present time because of its high nitrogen content. Third, Bryant anticipates that the improved air quality in the hog barns will result in lower mortality rates, more efficient conversion of feed by the hogs, and best of all, fatter hogs headed to market. The odor emanating from the storage lagoon has also been reduced, and Bryant says looking after the system has had minimal impact on his daily routine. Deshusses says that because the system meets stringent environmental performance standards, Bryant could one day expand his hog farm. The standards include the substantial elimination of odors, pathogens, nutrients, ammonia, and heavy metals as well as the total elimination of discharge of waste to surface and groundwater. Under state law, no farm can expand unless it installs a waste management system that meets these standards.

“This system has the potential for reducing the environmental footprint of hog farming, while creating new revenue streams for the farmers,” he says, “but I think we are really at the beginning of an exciting path.”

When asked if the system is something he could recommend to other hog farmers, Bryant says it is unlikely that farmers would be prepared to invest into the system on their own, but there would likely be interest if there were some form of state or federal assistance with the installation cost.

In addition to the project benefiting the farm financially, it also delivers a number of environmental and energy dividends. While meeting stringent environmental performance standards, it also reduces carbon emissions by about 5,000 metric tons per year by destroying methane that would otherwise be emitted from the lagoon. Methane gas is 21 times more potent as a greenhouse gas than carbon dioxide. The system also is expected to produce about 500 megawatt-hours of electricity each year.

Besides the global profile that Google’s involvement brings to the project and to Duke University, the university will also be able to use a portion of the carbon credits generated by the project toward its goal of becoming carbon neutral by 2024. Additionally, the project will act as a classroom extension, where some students will study the project’s design and its performance as part of their studies.

The Loyd Ray Farms project is a prototype. With the experience of this construction project under their belt, Deshusses adds that those involved in its construction believe that the cost to duplicate this installation on other farms could be between 20 to 50 percent lower. The goal now is to monitor the performance of the entire system and to present the information to other hog farms for their consideration. North Carolina is the second largest hog producer in the United States, with about 2100 permitted farms raising about 9.4 million animals per year.

“This system is serial number one, and the intent is that there will be other systems because we believe that it is a good system,” says Deshusses. “This is a full-scale system on a medium to large hog farm. We are hoping that the system will fulfill all its promises, that we can present it as an economically viable option for farmers, and that there will be more of the same.”

What’s significant about the Loyd Ray Farms installation is that it is being offered as an “open source” design, meaning that it isn’t patented. Replicating the concept is available to anyone willing to spend the money on their own farm or to businesspeople interested in taking the concept and offering its installation as a service to hog farms. In addition to an open design, the concept was developed with the intent of using easily accessible, off-the-shelf components. Deshusses says the only item in the design that farmers may find unfamiliar is the power generator.

Otherwise, the remaining components consist of pumps, valves and storage systems familiar to hog farmers that also aren’t necessarily specialized technology. In other words, the farmer can choose whatever pump brand he wants, as long as it meets the specifications outlined in the system design.

“There have been a number of creative and innovative solutions for handling hog manure, with some of them including composting,” says Deshusses. “They need sophisticated equipment that farmers are not likely to adopt because it just is not familiar to them,”

The liquid manure is collected in the conventional way in each hog barn, in storage pits below floor slats. The pits not only collect waste from the hogs but also any wash and fresh water used on a daily basis in the hog operation. Each storage pit is equipped with an overflow valve much like the overflow valve on a bathtub, meaning that there is constant gravity flow of some raw liquid manure through pipes from each barn connected to a central collection point, which in turn uses gravity flow to supply the anaerobic digester. Once a day, Bryant opens the valve on two of the nine barns to send a large volume of liquid manure into the digester, replenishing the water for the pits from an aeration basin, which stores some of the treated water discharged from the digester. Gas produced through biological digestion rises to the top, collects in a flexible dome, and is connected for use as fuel in the micro turbine. It consists of about 60 percent methane and 40 percent carbon dioxide. The liquid byproduct flows into the 1.1 million gallon aeration basin located next to the digester as raw manure is added to the digester, where the remaining nutrients in the water undergo further chemical transformation of the ammonia into nitrite and nitrate in the open-air environment. A portion of this water is recycled through the hog operation as wash water. The remainder is stored in the old storage lagoon and eventually used to irrigate farmland as organic fertilizer.

“It’s all designed to function with a minimum of moving parts,” says Deshusses. “So for any volume that enters the digester, a similar volume will overflow from the digester into the aeration basin, which is essentially a partial nitrification of the ammonia. And then that water is used to flush the barns.” Some water from the aeration basin can also be pumped back for reprocessing through the digester in the event that there is sludge built up in the basin.

There are also some pumps connected to the digester to promote mixing of the solid material.

The system is built with flexibility in mind so that if the micro turbine-generator needs to be shut down for a short time for service, the digester gas will simply accumulate under the flexible dome.

In additional to financial support from Google and Duke Energy, the university also received $500,000 from the U.S. Department of Agriculture and the North Carolina Department of Environment and Natural Resources Lagoon Conversion Program to construct the project.