December 2014                                                                                                             


Dairy Farming, Water Pollution, and the Anaerobic Digester

By Kim Buddington 

The “aroma” is a hallmark scent of the New England countryside. Unmistakable, unavoidable, and permeating, it is the smell of cows…or the smell of bovine manure. However, manure infiltrates more than just the senses of a person driving by a dairy farm. Improper management and disposal of the waste can have a terrible effect on this planet’s valuable natural resources as well as risking the health of many people, now and for many years to come.


There is an age-old decomposition method for the treatment of organic wastes known as anaerobic digestion. Using a specialized anaerobic digester unit, manure can be processed with the help of special microbes and turned into a renewable biogas (Clay 1). The question is this: is anaerobic digestion the best solution for managing manure and minimizing the environmental risks that go along with it? Furthermore, would installing an on-farm anaerobic digester be an economically viable waste management solution for the average dairy farm in the Commonwealth of Massachusetts?  


According to the 2012 USDA census of agriculture, there were 9,252,272 dairy cows involved in milk production on 64,098 farms in the United States. The waste that such a large number of animals produce is significant. For a typical milk producing cow, manure generation amounts to about 140 pounds every day (Ketterings,Giroux and Greenwood).


In the past, most dairy farms were small and milked a relatively small number of cows. But driven by economics and increased product demand, this has been and still is changing. Nowadays, over fifty percent of the milk in the United States comes from farms with 1,000 head of cattle or greater. Even though these farms still only represent about three percent of dairy farms nationwide, they dominate major milk markets (Grossman).

The larger the farm becomes, the more potential there is for serious environmental pollution. In Yale Environment 360, Elizabeth Grossman writes, “With the increased concentration of milking cows comes a corresponding concentration of manure production. And what happens to this manure is at the heart of the pollution issues surrounding the dairy industry” (Grossman). The more manure that is produced and concentrated in one area, the more chance there is for residual runoff from the surface to go into ponds and streams as well as leeching into the ground and fouling underground springs and wells. High levels of phosphorous from concentrated manure can cause algae blooms to become serious problems in lakes, estuaries and other bodies of water (Silveira, Vendramini and Sollenberger 2).

Manure, along with the phosphorous and nitrogen that are components of it, is very useful and important for nurturing and growing crops of all kinds. However, when manure that has been spread onto farm fields gets washed off and drains into rivers and other bodies of water, something called eutrophication can occur. Eutrophication is oxygen deprivation in a body of water.


Excess phosphorous and nitrogen from manure promotes the growth of algae, such as pfiesteria and cyanobacteria (Sharpley, McDowell and Kleinman 1). Rapid growth of the algae

then robs the water of oxygen, which in turn kills fish and other aquatic life. Additionally, algae blooms can turn drinking water toxic and make it unsafe for consumption by humans and livestock (Hill).  

The federal government as well as state governments have taken steps to help prevent this kind of pollution. For example, the EPA has come out with specific regulations for farms with more than seven hundred cows. However, rules like that only apply to very large farms. Smaller farms tend to be held under less regulation (Duhigg A1).

With so much manure being produced and not enough places to put it, the land is being saturated. In a New York Times article about the problems of dairy farm runoff and contamination of drinking water wells in Wisconsin, Bill Hafs, a county official in that state contends, “There just isn’t enough land to absorb that much manure, but we don’t have laws to force people to stop”(Qtd. in Duhigg A1).  

But passing more laws isn’t merely enough. In addition, the farms that milk over 1,000 cows are not the only ones to blame for water pollution. All agricultural operations, big and small, generate some degree of pollution and their operators need to make efforts to protect the natural resources around them. Clearly, finding a way to effectively manage manure remains problematic.


There isn’t just one strategy that is going to work for every operation, since every farm is different. Mark Rice of North Carolina State University explains, “Manure treatment technologies are often linked together to address several challenges faced by animal producers such as excessive nutrient on farm, manure runoff and odor”(Rice).

Is there a treatment method available that could possibly meet all three of those main criteria? This is where the process of anaerobic digestion that was previously mentioned comes into play. The use of anaerobic digestion as a way to treat organic waste is not a new discovery. The earliest available historical records point to evidence that the process was used 5000 years ago by the Sumerians for waste management. Since then anaerobic digestion has been used all across the world in varying capacities. As of 2014, there were at least 125 digesters working to break down manure in the United States and thousands more worldwide (Fennell 11).

The modern anaerobic digester is in essence a type of composting system. Both composting and anaerobic digestion accomplish the same task of breaking down organic waste. Composting uses oxygen to work, but anaerobic digestion does not. This is the vital difference between the two processes (“About Agreen Energy, LLC” Agreen Energy, LLC). 

While there are several different kinds of digesters designed for different types of waste or waste combinations, the basic process is the same. The effluent is pumped into the digester and held at about 101 degrees Fahrenheit where it ferments and breaks down. As the process continues, acid is produced by certain types of bacteria and then transformed into methane by additional bacteria. A careful equilibrium between the acid-forming bacteria and the methane-forming bacteria must be achieved in order for this intricate process to work correctly. If all goes well, the biogas produced, which is composed of thirty to forty percent carbon dioxide and sixty to seventy percent methane, is sent into a special generator where electricity is made (Clay 1-2; Ghaly and Al hattab 3-4).

There are a number of positve reasons for a dairy farm to explore implementing an on-site digester. The first and most obvious advantage to installing a digester is the production of renewable energy. Thanks to a digester, it is possible for a farm to use its own waste to provide for some, or even all of its energy needs. In some cases, selling electricity back to the grid is also an option. This can save the farm large amounts of money that would otherwise be spent on electricity, as well as provide an added source of income from sale of its homegrown energy (Clay 1; Jorgenson; Llelegi, Martin and Jones 1-5).

A second positive that the anaerobic digestion of manure has going for it is that research has shown that it is useful in lessening the amount of harmful bacteria such as E. coli in manure sludge, which can contaminate water. (Saunders, Harrison and Fortuna 1055) The authors of Pathogen Reduction in Minimally Managed Composting of Bovine Manure in the Waste Management journal acknowledge that, “Livestock and poultry manure are known sources of bacterial pathogens such as Campylobacter jejuni, Escherichia coli 0157:H7, Salmonella spp., and Listeria monocytogenes, that can be disseminated from sources via waterways, run-off, vectors, fomites and the air,” (Millner, Ingram and Mulbry 1992).

Since evidence shows that harmful pathogen amounts are reduced by the process of anaerobic digestion, this makes the semi-liquid material left over in the digester after the methane has been processed ideal for spreading on cropland as fertilizer. This fertilizer is also much more efficiently utilized by plants than raw manure. As a result, water runoff is drastically reduced (Llelegi, Martin and Jones 4; Jorgenson).

Another plus to installing a digester is that emissions of noxious odors are minimized (Frear and Dvorak 4; Hughes and Wilkie16). As urbanization increases, odor continues to be a major problem as the space between residential neighborhoods and dairy farms continues to shrink. In a bioenergy fact sheet from Purdue Extension, the authors point out, “Odor control is a key benefit in being a better neighbor” (Llelegi, Martin and Jones 4). Relations between farmers and non-farmers need to be kept positive, this can help facilitate people working together to come up with solutions to solve environmental problems and more.

While there are many positives to anaerobic digestion, it is not a perfect silver bullet. There are drawbacks and the technology is not necessarilt feasible for all. The biggest negative factor that works against the anaerobic digester is the extremly high cost of getting one started on a farm. This single issue disqualifies many smaller farms from being able to use this method profitably. In an article from National Hog Farmer, Charles Gould, an extension educator from Michigan State University reports, “An average U.S. digester nows costs $1.5 million,”(Qtd. in “Weighing Pros and Cons of Methane Digesters”-National Hog Farmer).

This obviously varies by state and Massachusetts is on the more costly end of the spectrum. According to William L Jorgenson, managing director of Agreen Energy LLC, a Massachusetts company that specializes in setting up digesters on dairy farms, the total average cost for getting started with an on-farm digester in Massachusetts is around three million dollars (Jorgenson). That is a lot of money for any farmer to shell out, and is next to impossible without loans and or grants.

Another problem with digesters is that they require large amounts of raw manure to work- and to work profitably.  In Massachusetts a farm that is only running a digester on manure would need to have at least thirteen hundred head of cattle or more for the digester to be profitable. If other wastes are also being treated with the manure, such as waste from food processing plants and restaurants, then two hundred fifty cows would be the minimum. The digesters in Massachusetts that are part of  Agreen Energy’s project run on a combination of manure (33%) and industrial food wastes (66%) (Jorgenson).  

That helps, but a cow herd size of two hundred fifty or more is still quite large when the average dairy herd size in Massachusetts is considered. According to the 2012 USDA agricultural census, the vast majority of dairy farms in Massachusetts reported having less than one hundred cows. That is also rings true for a large percentage of dairy farms across the United States. This, unfortunately, puts the anaerobic digester off limits for far too many operations.

Everybody agrees that manure needs to be managed in a responsible way in order to protect people and the environment. There is also no doubt that current methods need improvement. Although vast, exciting improvements have been made with the technology surrounding anaerobic digestion, there is still more work to be done. Charles Gould puts it bluntly, “If we have to depend on grant dollars or cost-share dollars in order to put digesters in, there is a finite amount of money available. So we are on a collision course here. Either we make digesters more affordable, or we have a limited number of digesters in the United States,” (Qtd. in “Weighing Pros and Cons of Methane Digestion”- National Hog Farmer).

There is yet another factor. In some situations, an anaerobic digester becomes the farm’s one and only option for manure management. Jorgenson points this out, “In some states the laws on nutrient management mean the farmer needs to invest in this type of abatement strategy, a digester, just to stay in business,”(Jorgenson). If the price of digesters doesn’t come down and funding becomes more limited, but environmental protection laws continue to grow more stringent, how many already struggling farms could this be the breaking point for?

In conclusion, the anaerobic digester system holds a lot of potential, if put into wide use, for environmental protection and for farm profitability. However, at this point in the technological development surrounding digesters, does it really benefit the farmer? Can it really help, especially in Massachusetts, to keep the average dairy farm viable? There are still many limitations. An operation with less than two hundred fifty cows can not adequately sustain a digester and the cost to install and maintain a unit is high.

Still, the future appears to be bright. Much progress has been made within the past years so it is just as probable that even more will be made in the near future. More sharing of digester equipment between dairy farmers and other industries is one aspect that is promising. That is a great way to get people working together on an issue, waste disposal, that effects everyone and the environment. The only way to perfect something is to keep working on it. What exists now is not flawless, but it is certainly a step in the right direction.

Works Cited

"About AGreen Energy, LLC." AGreen Energy, LLC. AGreen Energy, LLC, 2010. Web. 08 Dec. 2014.

Clay, Marianne. Animal Power: Turning Animal Waste Into Energy. Rep. Susquehanna Valley Center For Public Policy, 2007. Web. 18 Nov. 2014.

Duhigg, Charles. "Health Ills Abound as Farm Runoff Fouls Wells." New York Times 18 Sept. 2009, New York ed.: A1. 17 Sept. 2009. Web. 1 Nov. 2014.

Fennell, Donna E. "Anaerobic Digestion." Rutgers University, New Brunswick, NJ. Web. 18 Nov. 2014.

Frear, Craig, and Steve Dvorak. "Anaerobic Digestion and Nutrient Recovery." AGSTAR National Conference. Syracuse. Web. 18 Nov. 2014.

Ghaly, A.E., and M. Al Hattab. "An Innovative Farm Scale Biogas/Composting Facility for a Sustainable Medium Size Dairy Farm." American Journal of Agricultural and Biological Sciences 7.1 (2012): 1-16. Science Publications, 2012. Web. 18 Nov. 2014.

Grossman, Elizabeth. "As Dairy Farms Grow Bigger, New Concerns About Pollution." By Elizabeth Grossman: Yale Environment 360. 27 May 2014. Web. 10 Oct. 2014.

Hill, Cindy Ellen. "Lake Champlain Phosphorus Problem." VTDigger. N.p., 6 May 2012. Web. 1 Nov. 2014.

Hughes, Kristen and Ann C. Wilkie, eds. Cost-effective and Environmentally Beneficial Dairy Manure Management Practices. San Francisco: Sustainable Conservation. 2005. Web. 21 Oct. 2014

Jorgenson, William L. "Re: Digester Questions." Message to the author. 25 Nov. 2014. E-mail.

Ketterings, Dr. Quirine M., Joe Giroux, and Jon Greenwood. "Northern New York Research Evaluates Best Use of Dairy Cow Manure." Northern New York Research Evaluates Best Use of Dairy Cow Manure. Progressive Dairy Publishing, 2009. Web. 14 Nov. 2014.

Llelegi, Klein E., Chad Martin, and Don Jones. Basics of Energy Production Through Anaerobic Digestion of Livestock Manure. N.p.: Purdue University Extension, Sept. 2008. PDF. Web. 18 Nov. 2014.

Millner, Patricia. "Pathogen Reduction in Minimally Managed Composting of Bovine Manure." Waste Management 34 (2014): 1992-999. Science Direct. Web. 14 Nov. 2014.

Rice, Mark. "Manure Treatment Technologies for Livestock and Poultry Manure." Manure Treatment Technologies for Livestock and Poultry Manure - EXtension. Extension- America's Reasearch Based Learning Network, Oct. 2013. Web. 30 Oct. 2014.

Saunders, Olivia, et al. "Effect Of Anaerobic Digestion And Application Method On The Presence And Survivability Of E. Coli And Fecal Coliforms In Dairy Waste Applied To Soil." Water, Air & Soil Pollution 223.3 (2012): 1055-1063. Environment Complete. Web. 10 Dec. 2014.

Sharpley, Andrew N., Richard W. McDowell, and Peter J.A. Kleinman. "Phosphorus Loss From Land To Water: Integrating Agriculture And Environmental Management." Plant & Soil 237.2 (2001): 287. Environment Complete. Web. 2 Dec. 2014.

Silveira, Maria L., Joao M. B. Vendramini, and Lynn E. Sollenberger. "Phosphorus Management And Water Quality Problems In Grazingland Ecosystems." International Journal Of Agronomy 2010.(2010): 1-8. Environment Complete. Web. 2 Dec. 2014.

"Weighing Pros and Cons of Methane Digesters." National Hog Farmer. N.p., 10 Mar. 2011. Web. 18 Nov. 2014.

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