Could Dairies Double as Clean Power Plants?


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There is one big difference between Green Mountain Dairy and most other large milk farms: it doesn't stink. When I pulled into the well-tended barnyard in northern Vermont last week, there was not a whiff of evidence to suggest that the place is home to 1,800 dairy cattle.

I had dropped by to talk to Bill Rowell, who runs the operation with his brother, Brian, about the dismal financial conditions with which dairy farmers are coping (or in too many cases, failing to cope). But because I am a frequent—and angry—breather of malodorous discharges from a similar-sized herd housed a couple of miles from my house, my first question was: "Where's the smell?"

That sent Rowell off on one of his favorite tangents. He explained that no smell emanates from his cows because their manure is converted into methane gas, which is then burned in a generator on his property to produce enough electricity to power nearly 400 homes.

Converting cow manure into a renewable source of fuel is one of those rare situations in which everybody and everything wins—especially the environment.

Converting cow manure into a renewable source of fuel is one of those rare situations in which everybody and everything wins—especially the environment. Spreading raw manure on fields, as is the common practice, not only makes for disgruntled neighbors like me, but also pollutes both the water (as runoff) and the air (as it releases methane, a greenhouse gas that is between 20 and 50 times as effective at trapping heat as carbon dioxide).

As Rowell led me around four low-slung, green-roofed barns, he said that the 40,000 gallons of manure that his cows produce each day flows into a covered concrete anaerobic digester. He indicated a buried concrete structure about the size of a public swimming pool covered by a foam-like insulation material. Through an opening, I saw a foamy, brown slurry. Over the roar of a motor, Rowell explained that after the manure is held at 101 degrees for 21 days, the smell is gone, as are fly and other insect larvae, weed seeds, and most pathogens. The remaining solution is pumped into a separator.

We went inside a nearby building that was filled with conical piles of what looked like peat moss. Rowell cupped his hands and scooped up some of the "moss" and shoved it under my nose. The odor was acrid, a bit like ammonia, but mild and inoffensive. He explained that these separated solids were clean enough to be used as bedding for the cows or sold to garden centers and landscapers, saving Rowell $100,000 a year. "The liquids are held there." He swung his hand toward a nearly empty holding pond. "They are odor free, and when they are spread on fields, they are immediately taken up by plants, eliminating run-off."

But the real savings comes from the methane that is a by-product of the process. Instead of wafting into the atmosphere, Green Mountain Dairy's gas is used to fuel a generator that is as big (and loud) as a small dump truck. Running 24 hours a day all year long, the machine not only produces heat, but also four times as much electricity as the farm uses. The excess is sold to the local power utility.

Methane is the major component of natural gas, and burning it in an electrical generator does create carbon dioxide, a greenhouse gas. But on balance, cow-generated electricity is much less harmful to the environment than spreading manure and generating electricity from coal-fired plants and other sources.

There is one drawback to cow power: the initial cost. The Green Mountain Dairy system cost $2.2 million when it was installed in 2007. Of that, $750,000 came from grants, and Rowell estimates that the generator will pay for itself over the next few years. "We've gotten toward the end of the pioneering stage," he said. "The next step is to compress excess methane to fuel equipment in the fields."

In one important way, generating electricity from cow manure is a step back in history to the era when animal manure was viewed as a valuable fertilizer by small farmers. It was only the advent of huge, enclosed production systems that turned it into a noxious pollutant and foul-smelling "disposal problem."

And according to Rowell, there is another old-fashioned advantage to cutting-edge cow power. "Now, when our neighbors pass us on the road, we've realized they have five fingers—not one."