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A Dairy Making Sure Manure Isn’t Waste

“It takes a lot of energy to produce milk,” Albert Straus tells us almost immediately after we arrive at his dairy. He would know. Straus owns and runs the Straus Family Dairy and a nearby creamery in Tomales Bay, just north of San Francisco. With knee-high boots trudging through mud, Straus shows us the 300 cows he manages, a herd whose milk becomes cheese, ice cream, butter, and yogurt that gets distributed across much of the U.S.

That’s the clean story. Making sure that the rest of us get our ice cream requires Straus to deal with a less palatable part of farming. Every day, each of his cows produce 120 pounds of manure. Added together, it amounts to a mountain of manure that builds up, rain or shine.

Considering that dung contains lots of methane, a potent greenhouse gas, Straus decided several years ago that he’d tap the waste for its full potential. He built a methane digester on his farm. When he showed it to us, the digester looked simply like a bubbling pond enclosed by a large tarp. But the gas inside serves up 960 kilowatt hours of electricity each day, enough to power Straus’s entire dairy. And his electric car.

Digested methane becomes electricity when it’s burned in an engine or a turbine. When the pistons or turbine blades spin, energy can be drawn out. It’s a technical process but has a simple take-away: A voluminous waste product can become a commodity with value.

Straus isn’t the only farmer using a digester for methane. But his farm may be a model for other farms, especially larger ones, that have a constant stream of methane-rich manure. The whole system cost Straus around $355,000, some of which came via generous grants from the Environmental Protection Agency and the state of California. The investment, Straus’ staff says, has already paid for itself.