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The Promise and Peril of Cow Power

Anaerobic digestion is an innovative process that converts waste to energy. Is it too good to be true?

Anaerobic digesters, The River
Anaerobic digesters convert waste into energy.
Source: Flickr
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The Hudson Valley is one of the most productive and oldest agricultural regions in the United States, but, like farmland everywhere in America, ours is increasingly threatened.

A 2018 report, “Farms Under Threat: the State of America’s Farmlands,” by the American Farmland Trust and Conservation Science Partners, attempted to determine how much agricultural land was lost to development in the continental US between 1992 and 2012. The number they landed on was about 31 million acres, one-third of which was classified as highly productive and versatile farmland.

That may not seem like much—it’s about 3.5 percent of all the agricultural land in the lower 48 states. But the trend cannot be easily reversed, and development pressure is but one of many perils (unpredictable weather, environmental despoliation, and trade policies, to name a few) putting the squeeze on American farmers. Many are reacting by incorporating new methods and technologies to increase efficiency and streamline costs. One technology, in particular, has gotten a lot of recent coverage: anaerobic digesters.

Put simply, anaerobic digestion is a process that converts plant and animal waste into energy, with the added benefit of reducing odor from manure. Here’s how it works: Waste is left to ferment in an oxygen-free sealed tank (called a digester), where microbes convert it into two byproducts: methane-rich gas (biogas) and a nutrient-rich fertilizer (digestate). The biogas is chemically similar to natural gas, and can be burned to power generators for electricity and heat.

Anaerobic digestion is a cost-efficient way of creating energy while decreasing one’s carbon footprint—a solution straight out of science fiction for under-resourced farms. “For small dairy farmers, anaerobic digesters could be the sustainable energy technology to revolutionize manure management while cutting down farm energy expenditures,” writes Abigail Woughter of Cornell’s Small Farms Program in a 2014 article touting the benefits of anaerobic digesters for small farms.

Anaerobic digesters, The RiverCredit: Source: Wikimedia Commons
Schematic of an anaerobic digester.

In recognition of their promise, the New York State Energy and Research Development Authority (NYSERDA) last year announced $19 million in funding “to accelerate the use of anaerobic digester projects and clean energy technologies” on New York farms, claiming the technology would support Governor Andrew Cuomo’s goal to reduce greenhouse gas emissions 40 percent by 2030. This is on top of $26 million the agency has already given the sector.

And New York has caught the anaerobic-digestion bug. The tiny Sullivan County town of Tusten plans to purchase an anaerobic digester that will be powered by its solar array, which will make it the first municipality in the country with a solar-powered anaerobic digestion system. At the other end of the spectrum, the waste management company American Organic Energy, based in Long Island, is in the process of building what will be the largest anaerobic digester east of the Mississippi, according to the New York Times: It will convert about 180,000 tons of waste into energy per year.

Anaerobic digestion isn’t yet widely implemented anywhere, but its promise is particularly alluring for New York, where the number of small farms declined by 8 percent between 2007 and 2017, while over the same time period production costs rose 23.5 percent, according to the 2017 US Department of Agriculture Census of Agriculture. A New York agriculture report by State Comptroller based on that data and issued in August of 2019 named “threats from climate change, such as summer heat stress, rain intensity, and increased flooding risk” as “emerging challengers” for New York farmers.

Eco-friendly, or greenwashing?

But anaerobic digestion is not without some significant potential snags. For one, digesters are very expensive to build and maintain, and there are few farms—certainly almost no small farms—that can afford to invest in one without outside funding. Government money spent in one place is generally government money not spent elsewhere. So do anaerobic digesters justify the cost?

Critics point out two main problems. The first is that while the energy from digesters may be “renewable,” it’s not really “green.” Biogas made via anaerobic digestion is comprised of methane, carbon dioxide, and trace amounts of other gases. Burning them converts the methane into carbon dioxide, which is released into the atmosphere along with other air pollutants. It’s only considered to be “green” because the EPA calculates methane to be 25 times more potent a greenhouse gas than carbon dioxide, so burning it for fuel and releasing carbon dioxide into the air is still considered to be a greenhouse gas “reduction,” as Jessica McKenzie explains in a recent article for the New Food Economy headlined “The misbegotten promise of anaerobic digesters.”

McKenzie’s investigation is, among other things, an excellent example of how the classificatory squishiness of terms like “green,” “environmentally friendly,” and “clean energy” can obscure the actual science behind the technologies and methods they describe. It’s also an example of how solutions to climate problems that don’t address systemic issues are temporary solutions at best.

Which gets us to the second main problem. As McKenzie asks:

But are digesters even necessary? Around 80 percent of digesters in the US are on dairy farms, but methane emissions from manure deposited on fields from pastured cows are virtually nil. Manure releases methane only when it decomposes in oxygen-free (anaerobic) conditions, like a pit or lagoon. Most of the livestock farms that store manure in pits or lagoons are large concentrated animal feeding operations (CAFOs) where animals are confined for more than 45 days of the year. So, critics say, anaerobic digesters are solving problems only created by large-scale factory farming in the first place, problems that are avoided in more sustainable systems, especially pasture-based ones.

Some environmentalist groups, including the World Wildlife Fund and the Environmental Defense Fund, say anaerobic digesters make the best of the bad situation we currently find ourselves in. Others, like Food & Water Watch, “say the government is greenwashing and subsidizing factory farming at the expense of sustainable producers and genuinely clean, renewable energy like wind and solar,” McKenzie writes. In other words, anaerobic digestion perpetuates one of the main causes of the climate crisis, under the guise of a solution. Given the scarcity of both time and resources to devote to true solutions, anaerobic digestion may be seen as just another problem.