Andreas Aluia- Forestry
Sean Davenport- Environmental Science
Haley Goulet- Animal Science
Picture this. Miles of rolling green fields sprawled out in front of you, dappled in hundreds and hundreds of black and white cows. Their heads low as they graze the young grasses covered in early morning dew. Behind you the farmer is preparing the barns for the cows return in the afternoon. Each breath of air making you feel renewed with the peace and clean air of the countryside. But how clean is it?
Mixed into the smell of grass and hay are invisible gases. Which have gradually been accumulating because of the cows running around in front. The gases have accumulated so much in recent years that it is starting to pose a serious risk to the future of the planet you rely on. The cows filling the field are all releasing huge quantities of methane, alongside the millions of other cows that inhabit the planet.
In the last century the amount of greenhouse gas in our earth’s atmosphere has increased dramatically. A popular visual used to demonstrate these trends is the hockey stick graph. The beginning of the graph is largely flat but spikes up at the end, in the shape of a hockey stick, the visual measures earth’s surface temperature. dramatic increase in methane (CH4) starting in 1920 all the way through this year (Pearce, 2010). The hockey stick model has been reviewed and studied but a wide range of climate scientists and environmental experts. However the conclusion holds that the 20th century is drastically warmer than any other point in our planet’s history (Cook, 2016). New technology and infrastructure are part of the problem but when livestock and manure emissions were combined, the agriculture sector was the primary source of CH4 emissions in the US. Cattle especially contributed to this trend because of their large size and specific digestive system which releases comparably large amounts of methane (“Overview of greenhouse gases”, 2018). In 2011 the projected contribution of methane from cattle was 11% lower than what their contribution actually ended up being (Agence France-Presse, 2017).
When not impacted by human activities such as agriculture, greenhouse gases are released through natural processes and do not pose serious risk. The 20th century has brought an increase in human population and activity which has in turn made greenhouse gases a problem. While much of the conversation surrounding greenhouse gas emissions concerns carbon dioxide, methane emissions require just as much attention and can be overlooked in comparison. Methane is 25 times as powerful a GHG as CO2 (Brander, 2012). Greenhouse gases are usually measured in terms of carbon credits, which helps to put methanes strength into perspective. If a 100 cow farm is producing 971 Mg CO2, of methane (Chianese, 2009). Their global warming potential is that number multiplied by 25, methanes relative strength, so their emissions should actually be quantified as 24,275 Mg CO2 when discussing methanes warming potential. This means that even small emission sources of methane should be taken seriously. Unfortunately the cattle industry is no small source.
The average cow emits anywhere from 4.68 to 9.49 cubic feet of CH4 per day (Ishler 2016) converting that amount to mass shows cows release roughly 0.07 to 0.15kg of methane daily. Now to further quantify, it is important to realize that the United States alone is home to 95 million cattle as of 2018 (“Cattle inventory on January 1”, 2018). So in the US daily cows are emitting 6.65 to 14.25 million kg of methane. To put this in perspective, burning one gallon of gasoline creates roughly 9 kilograms of CO2, which is about three times more than the methane emitted by cows when adjusted for methane’s greater warming potential. Trends worldwide demonstrate the powerful effect of the cattle population on methane emissions. Developing regions in Africa, Asia, and Latin America experienced a 121% increase in livestock numbers from 1890-2014. In the same amount of time, they went from contributing 51.7% of the global total CH4 emissions to 72.5% (Dangal et al., 2017). The methane is released from cows because of their digestive system.
Methane is produced from cattle through a digestive process called enteric fermentation. Cattle are ruminant animals which means their digestive system includes 4 stomachs. One of these stomachs is called the rumen and this stomach’s digestive contribution is primarily fermentation of food by anaerobic microbes. The microbes break down feed material that enters the rumen and release methane as a byproduct of the process (“Enteric fermentation–greenhouse gas”,1998). Enteric fermentation is essential because of the high cellulose content in cow feed that is otherwise indigestible. As methane is released from the food in the rumen the cow then releases it into the atmosphere through belching, flatulence, and manure (Parkhurst, 2016).
Belching releases the greatest percentage of methane from the cow. Part of a cow’s digestive process includes eructation. The process by which a cow throws up the food in its rumen, chews it again (chewing cud), then swallows it again to continue the fermentation process. Eructation releases the equivalent of 132 to 264 gallons of ruminal gas daily. This gas is composed of 25.8% methane gas, as well as smaller percentages of other greenhouse gases and 65.5% carbon dioxide. (Ishler, 2016). But again it must be accounted that methane is 25 times stronger than carbon dioxide making its relative warming strength equivalent to 670%. This creates an immediate difficulty in the context of agricultural methane mitigation. Importantly all of a cow’s carbon footprint does not lie entirely in their burps and farts. After exiting the body, cow manure itself presents a significant source of livestock methane emissions. This methane, unlike that naturally produced in the guts of cattle can be reduced and even used by farmers.
Manure is an important aspect to methane emittance as a byproduct of cattle digestion. Containing 12-17% of the overall gas in the air emitted from cattle (Podkówka, 2015). Though it might not contain the majority of manure it is easier to manage than flatulence or burping as it is physical material release and not a gaseous release. The amount of methane produced from the same unit of ruminant manure is variable based on its composition, the method of storage, and climatic impacts (Kariyapperuma et al., 2018). The average cow produces 120 lbs of liquid manure daily so if a farm has 200 head of cattle and they produce 120 lbs of manure daily that yields 24,000 lbs of manure each day for a relatively small cattle farm! (Jun et al., 1996) It becomes essential with such volume to dispose of it properly. The majority of dairy farms store manure in liquid systems which create anaerobic environments similar to the rumen which breaks down the feces and produce methane. (Prajapati & Santos., 2018; Kariyapperuma et al., 2018). The current manure management techniques popular across the United States have proven themselves ineffective, and with this being the most treatable source of livestock methane emissions a solution must be established. One of the most reasonable solutions to this manure management problem is the anaerobic digester.
Our goal is to decrease the amount of methane produced by anthropogenic sources by passing a law that would enforce farms with more than 500 cows to install an anaerobic digester within a twenty-year time frame. The energy produced from waste would be bought back from the farm, which would in turn benefit the farm by recycling the waste from its cows and ultimately returning a profit. An anaerobic digester would be beneficial for all farms with high numbers of cattle because it takes food waste and manure and it converts sugars, fats and other compounds into a renewable energy source, biogas. One example of this process in practice is seen at Barstow’s Longview Farm, where their anaerobic digester powers a 300 kW engine, annually producing more than 2,100 Mwh of electric energy, and 30,000 tons of odor free organic liquid fertilizer (Barstow Longview Farm website). We believe that implementing this anaerobic digester law provides a safe, clean, and efficient way to process the waste of ruminant farming, ultimately decreasing methane emissions while also having a huge positive impact on farms.
The average cow produces roughly 120 lbs of manure per day. The amount methane produced by the manure entirely depends on type of cattle, diet and temperature of the cattle’s living environment. Of all the gas produced by manure, 65% to 95% of that gas is methane when the manure is in a warm, wet environment. Cold, dry manure gas emissions differ drastically with only 1% of gas emissions being methane (Jun et al., 2002). If a farmer decided to collect all the manure from his cattle and spread it on his crop fields as fertilizer on a hot summer day into the moist soil, the manure would emit 65-90% of methane into the air in comparison to other manure management practices. Other practices currently include distribution on crop fields using a tank wagon that spreads liquid manure or a dry manure spreader. There are also manure storage options such as enclosed wall areas, above ground tanks or storage ponds (Manure Management Choices, 1998). Many of these are common practices, but are not effective because, when exposed to open air, naturally occurring bacteria converts manure into methane that is emitted into the air. Similar to how yeast converts sugars into alcohol. Liquid systems will freely release additional methane into the atmosphere (Petersen, 2018). Manure management is an important source of emissions of trace gases in the United States, which have increased from 29.3 Tg CO2 in 1990, to 45 Tg CO2 equivalents in 2008 (USEPA., 2010; Delgado et al., 2013). Manure and enteric fermentation alone are responsible for 54% of the total agricultural greenhouse gas emissions (Wei et al.).
We’ve found that Anaerobic Digesters (AD) are a great answer to minimizing the amount of methane released into the atmosphere. Anaerobic digestion is a natural process, by which materials such as animal manure, food scraps, fats, oils, greases, and biosolids are broken down in a large tank through four different stages (“Emissions factors for greenhouse”, 2018). The first stage, Hydrolysis, breaks down carbohydrates, fats, and proteins into simple sugars, fatty acids, and amino acids. The second stage is Acidogenesis, through which the single molecules, fatty acids and amino acids are broken down further into alcohols and volatile fatty acids with by-products of carbon dioxide, ammonia and hydrogen sulfide. During the third stage, Acetogenesis, those volatile fatty acids and alcohols are converted again, this time into hydrogen, carbon dioxide and acetic acid. In the fourth stage called Methanogenesis, methanogenic archaea convert the remaining hydrogen and acetic acid into methane and more carbon dioxide. All these stages were found and explained by the organization called “Anaerobic Digestion and Bioresources Association”.
The methane and carbon dioxide biogases captured from the fourth stage in AD can later be burned and used to power a wide variety of industrial and residential outlets. (“Emissions factors for greenhouse”, 2018). With an installed AD, farmers are able to turn food scraps and cow manure into power that they utilize themselves and sell to power companies. Besides the power produced from the anaerobic digester farmers are also able to use the digestate material, the leftover organic material that comes out of the digester. Digestate can be used as bedding for livestock, a soil amendment, or as fertilizer with no traces of methane production. This form of manure management provides a very effective way to trap the methane produced by manure otherwise released into the open atmosphere. In essence every product of an anaerobic digester can be used by the farmer or sold, thus inevitably providing a huge resource that can cut down overall costs on the farm in the long term.
In 2006 California implemented similar legislation to what we are discussing with mixed reactions. Dairy farmers were already struggling with years of drought, dropping milk prices, and rising labor costs and were not happy about the legislation. Farmers were confident that a single state implementing these laws would not make a meaningful impact on the environment and that the law would simply push farmers to relocate out of state rather than build an anaerobic digester (Chea, 2016). The law generated by Gov. Jerry Brown pushed for a lofty goal of reducing methane emissions by 40% by 2030. Lawmakers believed that 75% of that reduction should come from dairy farms. Further that the reduction of methane could be converted into useable forms of energy (Gustin, 2016). Importantly the law was backed by outreach programs, grant programs and economic incentives making farmers a little more apt to strive to reduce their emission with government help. California’s goal in addition to massively reducing their carbon footprint statewide was to provide a model for other states to take up and reduce their own carbon footprint (Hall, 2018).
Anaerobic digesters are an expensive undertaking and for struggling farmers it might seem like an impossible task. It can cost anywhere from $400,000 to $5,000,000 with the typical unit coming in at $1.2 million (“Anaerobic Digesters”, 2018). Plus the additional hours of overtime labor and use of land to hold the 600,000 gallon unit (barstow’s farm). This is where California’s model law will come into play with this nation wide legislature. Government aid in the form of grants, and outreach programs will provide substantial economic support for the additional lofty cost involved in building an anaerobic digester. It is equally important to remember that farms will see significant return after the unit is built and in use. The anaerobic digester pays for itself in the long term eventually bringing significant revenue into the farm. Barstow’s Longview Farm saw their anaerobic digester as an opportunity to save their family dairy farm. They are able to sell some of that energy using net metering programs. These programs connect energy producers, like farms with anaerobic digesters, to electricity companies who buy the energy and sell it to homeowners (“Massachusetts Net metering”, 2018). This practice is something that farms like Barstows use to revitalize their farms in an economy that is putting many family dairy farms out of business.
According to the American Biogas Council, in the U.S. there are over 2,100 sites anaerobic digesters: 247 of those are on farms. It is projected that there are hundreds of thousands and potentially over a million AD’s in the entire world, with Antarctica standing as the only continent unable to support this process due to cold temperatures (American Biogas Council., 2018). Countries like India, China and some Western European countries have been employing digesters for decades. The Biogas Council projects there are 8,241 dairy and swine farms ripe for development of AD. Installing an AD on a farm costs approximately $1.2 million dollars, but that price changes depending on the number of cows on the farm, the climate in the area, and the amount of methane the herd produces. Many capital costs for building an AD can be subsidized by grants or low-cost loans (Agstar EPA). With the price to install and maintain an AD, we decided to not affect small family run farms, instead we seek to encourage farms with 500 or more cows to install an anaerobic digester within a twenty year period. Farms with higher numbers of cows produce more methane, and would likely be more readily financially equipped to move forward with installation. This in comparison to small farms, such as Mapleline Farm in Hadley, Massachusetts, which is a family owned farm started in 1904 and currently rearing 200 cows. The cost of an AD would prove strenuous on the operating budget of such a small farm, and 200 cows do not produce nearly the equivalent in methane emissions as a farm rearing 5,000 cows.
The way in which the cattle industry operates in today’s world is, quite frankly, unsustainable. For an industry as critical as livestock raising, it is in providing the nation with affordable, quality food products, the sheer quantity of cattle and the methane they themselves and their waste creates is paints a very serious problem. Rising global temperatures is something most people hear about daily, and many try their best to avoid environmentally damaging products and activities. How exactly does one ensure that the food they put on their plate has as small as possible of a carbon footprint? With the adoption of anaerobic digesters, everyone benefits. By capturing and reusing both the gaseous and solid byproducts of cattle manure much of the methane from its fermentation process is prevented from entering the atmosphere and instead recycled for power. Adapting anaerobic digesters for use on all large farms within 5 years of ratifying this solution will be the future of curbing the cattle industries methane emissions and keeping farms alive. The anaerobic digester will not only decrease methane emissions produced by the cows, but also provide farmers with an extremely valuable tool that allows them to see great returns from recycling livestock’s waste.
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