Don't think of manure as simply a waste product. It can provide nutrition to crops, improve soil quality and provide renewable energy in the form of biogas. Turn to page 6 to read more about making the most of this valuable resource.
Photo by Bronwyn8/istockphoto.com.
Animal manure must be thought of as a resource that can provide economic benefits without adversely affecting the environment, rather than as a waste product that must be disposed of in any way possible. When properly managed, manure will provide nutrition to crops, improve soil quality and provide renewable energy in the form of biogas. Each of these options offers potential as an additional revenue stream for the farm.
Handled or disposed of incorrectly, manure becomes a point source environmental contaminant. Large, confined animal operations, such as dairy farms, are now required in many areas of the country to have nutrient management plans that specify how manure is being managed and disposed of. Whether large or small, animal agribusinesses all have the potential for some degree of environmental pollution if manure is mishandled.
The two primary pollutants of concern in manure are nitrogen and phosphorus, even though, ironically, both of these elements are necessary for plant growth. However, too much nitrogen and phosphorus coming from improperly stored manure, or from uncontrolled rain runoff, can contaminate lakes and waterways with too much "fertilizer," causing algae blooms that rob water of oxygen and kill fish. If too much nitrogen finds its way into aquifers, it can convert to nitrate, which is known to affect human health.
Steve Jones with the digested solids coming from the digester at Joneslan Farm in Hyde Park, Vt. The system is designed to generate 65 kilowatts of electricity at full capacity.
Photo by John Hibma.
Beginning in 1972 with the Clean Water Act, the U.S. federal government, through the Environmental Protection Agency (EPA), has been regulating pollution in the nation's waterways and water sources. Manure management in animal agriculture, with its tendency to pollute with nitrogen and phosphorus, along with the potential for bacterial contaminants such as E. coli and salmonella, is closely monitored in the interest of public health. In recent years, air quality issues from ammonia emissions and methane coming from manure decomposition have also come under the radar of the EPA.
Manure must be stored, handled and applied to land in such a way that it poses no risk as a contaminant. (Some may consider manure a hazardous waste.) On many farms, the stabilization and storage of manure amounts to collecting it into piles, allowing it to dry (or keeping it from getting wet), and preventing effluent and runoff from getting into waterways. When seasonal and weather conditions permit, the manure is most often applied to cropland. On larger farms, storage ponds or lagoons are used to store liquid manure. Liquefied manure, or slurry, is highly odiferous, which becomes objectionable in populated areas.
The most popular and the least costly way to store and manage manure, especially on small farms, is through composting. Composting is essentially the breaking down of organic matter by bacteria and other microorganisms, mostly in a moist, aerobic environment. In its basic form, manure is an organic compound that, when properly composted, becomes a valuable source of nutrients that can be returned to the land and used to fertilize and improve soil quality. Most composting systems will introduce other organic components, such as dead leaves, grass clippings, sawdust and even food waste to improve the quality of the compost.
All animal operations, and dairy farms in particular, produce a lot of manure. A mature dairy cow is estimated to excrete about 8 percent of her body weight each day in manure. That means a cow weighing 1,400 pounds drops over 100 pounds of manure daily. A 100-cow dairy herd produces over half a million gallons of liquid manure each year.
In Bozrah, Conn., dairy farmer Texas Moon milks about 40 cows. Three years ago, Moon renovated his existing cow housing, demolishing an old freestall barn that was about ready to fall down and replacing it with a bedded-pack barn. Moon knew that federal and/or state regulations would eventually affect all dairy farm operations and decided to be proactive in his planning of manure management with a more environmentally friendly and sustainable way of dairy farming.
A bedded-pack housing system provides a dry, comfortable living environment for cows while essentially composting manure as it accumulates over time. Moon decided that due to the size of his herd, and the fact that he has enough land to rotationally graze the herd much of the year, a bedded-pack system made the most sense for managing manure. His main reason was to eliminate dealing with liquid manure, converting it to a high-quality resource available for fertilizing his pastures and hayfields - minus much of the smell.
To compost correctly, the manure needs to be mixed with other organic material and just the right amount of moisture to sustain the heating/oxidation process. Moon mixes sawdust with the manure based on temperature and moisture conditions, and rototills the pack every day or so. Urine acts as the wetting agent to keep the pack moist and reactive. Fresh manure from the stanchion area, holding pens and lanes is added directly to the pack. The pack must maintain a core temperature around 100 degrees Fahrenheit to complete the composting process. During the winter months, heat from the pack keeps the barn cozy for the cows.
The bedded pack measures 125 by 38 feet, leaving a total of 4,750 square feet of loafing space for the 40 milk cows and a few dry cows. During the winter months, when the cows are in the barn continuously, the pack grows to over 2 feet high as the manure and sawdust accumulate. This amounts to about 350 cubic yards of composted manure available for spreading on fields throughout the year.
With his bedded pack and composting system, Moon maintains a significant amount of control over the nitrogen excreted from his herd. There's no chance for liquid manure spills from ponds that might wind up in the local waterways. The 60 acres of pasture and hayfields receive the majority of the compost, with a small portion going to neighborhood gardens.
From left, Brian Jones, Steve Jones and Nina Kshetry, anaerobic digestion project manager for UEM, Inc., in front of the manure digester at Joneslan Farm.
Photo by John Hibma.
In Enfield, Conn., Jack Collins and his family milk about 80 cows at their Powder Hill Farm. In 1992, Collins and his wife, Mavis, were making plans to open an ice cream store, but they knew something had to be done about the "stink factor" if they expected anyone to come to the dairy and buy ice cream. He made arrangements with the town and began composting the manure from the dairy herd by mixing it with leaves collected by the town in the fall.
An experimenter and a good record-keeper, Collins soon found that the hayfields and cornfields where he applied his compost were, in many cases, outperforming those where he applied commercial fertilizer. Shortly thereafter, a local chrysanthemum grower tried some of the compost and was thrilled with the results. Word began to spread around town, and Collins found himself in the compost business.
He then took his composting venture to the next level with a standardized recipe, built a screening machine, and began producing a premium, garden-quality compost that recently received organic certification by the Northeast Organic Farming Association (NOFA). Today, Collins sells every pound of composted manure - by the bag or in bulk - that he doesn't need for his own crops. What began as an attempt to control odors on the dairy turned into another source of income - and people keep coming back for ice cream too.
Since manure is a carbon-based organic material, it has the potential to produce biogas that can be used to produce energy in the form of electricity and heat. The anaerobic decomposition of manure produces methane - the same as natural gas - which, when managed correctly, will power engines connected to an electrical generator that in turn is connected to the local power grid.
Biogas generated in a manure digestion system consists of about 60 percent methane and a small amount of hydrogen sulfide, with the remainder being carbon dioxide. When burned in an engine, it produces about 60 percent of the power available from pure natural gas.
Any animal agriculture operation can produce methane from animal manure. The challenge with producing methane is that it's costly to install the equipment needed for collection, storage and generation. Economies of scale and return on investment become central factors as to whether farms can afford to install this technology.
In Hyde Park, Vt., Joneslan Farm, a dairy farm milking 230 cows and owned by the Jones family, crunched the numbers and decided that a methane-generating system at their dairy was doable. With the help of UEM, Inc. (http://www.uemgroup.com), a company specializing in wastewater treatment and anaerobic digestion, the Joneses completed construction of their system in August of 2012.
A prefabricated equipment and control center.
According to Nina Kshetry (firstname.lastname@example.org), anaerobic digestion project manager for UEM, a key consideration in planning a digestion system is sizing the components properly. You don't want to oversize a system, but you also don't want to undersize the system and limit potential revenue coming from the generation and sale of electricity. The major components of a digestion system are: collection and storage tanks, pipes and pumps, hydrogen sulfide removal, manure digestion tank, engine and generator.
The Joneslan system is designed to generate 65 kilowatts of electricity at full capacity. The 250,000-gallon digester tank is a belowground pit, 72 feet in diameter at the surface and about 16 feet deep. The tank is filled with manure slurry and sealed, top and bottom, with a heavy geomembrane. The pit produces methane continuously, which is fed into a GM industrial engine. According to Brian Jones, who co-owns the farm with his brother Steve Jones, the Vermont Electric Cooperative is currently paying the farm 16 cents per kilowatt-hour.
In addition, the spent manure solids from the digester are dewatered through a screw press, and the dried solids are used for bedding in the free stalls, significantly reducing bedding expenses. A portion of the heat generated from the engine is used in the milk barn. The dried solids that are unused will continue to compost, and the Joneses have the option of developing a market for that as well.
These systems come with a high price tag, but federal and state grant money is available in varying amounts in different states to help with installation. UEM targets states where there's a proactive movement toward getting more digesters on line, and the company continues to study the options available and find solutions that make it increasingly cost-effective to use biogas for energy production.
Kshetry says the economic feasibility of installing manure digestion systems on dairy farms is highly dependent on an individual state's policies for renewable energy. She notes that Vermont is one of the more proactive states currently encouraging renewable energy from agriculture; there are some states that offer no funding for renewable energy projects. In an effort to bring down the cost of methane systems, UEM focuses on the standardization of system designs by incorporating common designs for different capacity ranges and eliminating the need to redesign the system for each project, so it's more affordable for small to midsize farms.
Currently, economies of scale tend to favor herd sizes of 100 cows or more to justify the investment. Other options, according to Kshetry, include augmenting a digestion system with commercial food waste that is rapidly degradable (e.g., restaurant waste or grocery store produce and expired products) to increase methane generation. With potential "tipping fees" for food waste providing additional revenue, and depending on the funding available, smaller dairy farms might be able to justify the construction of a system. Essentially any size farm with animals could benefit economically from bringing in off-farm organic substrate to increase methane production.
Our world has reached a point where all of the resources needed to produce energy and food will continue to become scarcer. Renewable energy sources and options, and the technology to incorporate their application, must be seriously considered. All animal agriculture businesses should explore the options for utilizing manure, and take advantage of this resource to potentially increase revenue while at the same time helping to keep the environment clean.
The author is a dairy nutritional consultant and works for Central Connecticut Cooperative Farmers Association in Manchester, Conn.