The Power of Poop

  • By Anna Rothschild
  • Posted 10.08.15
  • NOVA

In this episode of Gross Science, field reporter, Elizabeth Gillis, goes to a dairy farm and a waste water treatment plant to learn how to turn poop into heat, electricity, and fertilizer.

Running Time: 03:40


The Power of Poo

Posted: October 8, 2015

Anna Rothschild: Today we’re gonna do something a little different. Field reporter and Gross Science intern, Elizabeth Gillis is here to tell us about the ultimate in recycling.

Elizabeth Gillis: Recycling poop!

Rothschild: I’m Anna Rothschild and this is Gross Science.

Gillis: At any given time, about three hundred cows call Jordan Dairy Farm home, meaning there’s definitely no shortage of manure. Luckily, at this farm they know what to do with it.

Jen McDonnell: We combine manure from the cows and source-separated organics, or food waste, to produce energy and fertilizer.

Gillis: You see, when animals poop, they don’t just release feces. They also release microorganisms that feed on the fecal matter. And a few of these microscopic creatures produce an energy-filled gas called methane as a bi-product of their digestion. Usually, the methane floats up into the atmosphere and contributes to global warming. But when cows at Jordan Farm poop most of it falls through grates in the floor of the barn. It gets pumped a few yards away to a giant tank called an anaerobic digester, where all the methane gets funneled into an electricity-producing engine.

McDonnell: Some of the power is used right here on the farm and the rest is pushed back into the electrical grid for others to use.

Gillis: Inside the digester, all this waste takes part in a process called anaerobic digestion. Essentially the organic waste gets eaten by microbes, some from the poop itself, and others that are added to kickstart the process. The microbes release methane, which is converted into electricity. But poop’s not the only thing thrown into the digester. Other types of organic material, like food waste, gets thrown into the digester, as well.

McDonnel: They like ice cream more than they like celery. If we had ground up celery you wouldn’t get as much energy out of that as you would out of ice cream which makes sense, because you know, there’s more calories in that.

Gillis: To keep all these organisms happy, the digesters have to be anaerobic, or oxygen-free. And they need to be kept at a temperature of around 100 degrees Fahrenheit.

McDonnell: When the engine’s running it actually produces heat as well as electricity, and we capture some of that heat to keep our digester warm. So it’s a way to reuse all the bi-products coming out of the system.

Gillis: After the methane is captured, the brown slurry, or digestate, that's leftover makes an awesome fertilizer.

McDonnell: It still has a lot of nutrients in it, so nitrogen, which is really good for plant growth. So we’re able to use the digestate right here on the farm to grow corn for the cows, hay for the cows, that will keep the cows fed and keep them producing the manure that we can put back into the digester.

Gillis: At Jordan Farm, the digester is at the center of a pretty simple closed system. But it doesn’t just work on this scale. In fact, everything that’s flushed or drained near Boston, Massachusetts ends up at here.

Dave Duest: Welcome to the Deer Island Treatment Plant. My name’s Dave Duest. I’m the Deer Island Director.

Gillis: Here, sewage from about 2.3 million people gets treated using huge anaerobic digesters. And the result is the same as on the farm: methane that provides heat and electricity, and fertilizer, which in this case is sent to a factory where it becomes tiny pellets.

Duest: Everything’s getting cleaned. It’s the ultimate in recycling facility. We try to take the nastiest stuff that you can send us and clean it up and make it environmentally beneficial.

Gillis: So what I found out is that poop isn’t just waste. When you flush the toilet you might be feeding trillions of microscopic creatures, producing energy, and fertilizing our nation’s farmlands.

Rothschild: Ew.



Host, Producer
Anna Rothschild
Reporter, Writer, Animator, Editor
Elizabeth Gillis
Many thanks to Jen McDonnell and Dave Duest.
Music: “The Gold Lining”
©Broke for Free


Original Footage
@WGBH Educational Foundation 2015
Image of global warming
Flickr/NASA on the Commons
Additional footage of digestate
Provided by Shannon Carroll
Additional images of Deer Island
Provided by Ria Convery, Deer Island Treatment Facility


(used with permission from author)
Squeak Pack/squeak_10
All other sound effect created by Elizabeth Gillis
Produced by WGBH for PBS Digital Studios


Poop Illustration
©WGBH Educational Foundation 2015


Want more info?

Jordan Dairy Farms:

Deer Island Treatment Plant:

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