How Ben & Jerry’s is recycling food waste into energy

It may sound like the stuff of sci-fi movies, but diverting food waste from the landfill and converting it into electricity has become a real thing, and that conversion can help reduce climate change. William Brangham recently visited a Vermont ice cream factory and the operations next door to find out how it works. At the Ben and Jerry's ice cream plant in St. Albans, Vermont, they can churn out over 100 million pints of ice cream a year. And to assemble each of their dozens of different flavors, there are precise amounts of added cream, some chocolate perhaps, or maybe chocolate chips. But key to the whole operation is keeping those distinct flavors separate. Say you are making Chunky Monkey in the factory, and then the next flavor comes up, and it's Cherry Garcia. You don't want to mix Chunky Monkey with Cherry Garcia. Jenna Evans is Ben and Jerry's global sustainability manager. When you push one flavor out with a little bit of rinse water, that extra flavor that was left over in the pipes gets pushed into a barrel that gets stored as a waste ice cream product. Once that waste is collected, Ben and Jerry's has to figure out what to do with it. Historically, many organic wastes have been sent to landfills, especially food waste. Eric Roy is an ecological engineer at the University of Vermont. Once that food waste ends up in a landfill, it can produce methane that can escape to the atmosphere. And when that happens, that contributes to climate change. Methane is a potent greenhouse gas. It turns out there's an alternative process that works a lot like our own bodies do when we eat. It's called anaerobic digestion. We eat food, and it is processed in our gut. In this case, we're feeding the food waste to a large, constructed gut that's full of microbial life. And that microbial life is digesting the material and turning it into methane gas, which we can then capture and use as an energy source. Right next door to the Ben and Jerry's plant, in those shining steel towers, is a new anaerobic digester, one of over 2,000 nationwide. This facility receives up to 50,000 gallons a day of waste. Purpose Energy CEO Eric Fitch says most of that waste is pumped directly from the Ben and Jerry's facility. The wastewater goes into these big tanks, the bioreactors. Inside the bioreactors, there are bacteria that just metabolize whatever we're feeding it. This is our raw influent, what we're feeding into our digester. You know, very dirty, nasty-looking water. Justin Filio is a wastewater operator at Purpose Energy. So in our digesters, this is what it looks like. That's just the color of our bacteria. So this is a sort of a microcosm of what's happening in the huge tanks out there. Yep. And the little air bubbles you see in there are them producing methane. The digestion process produces methane and carbon dioxide, which, if allowed to just leave the reactor, would contribute to climate change, but when captured and used, is called biogas. The biogas comes off the top and then it goes into this container over here that has a big engine in it. The engine turns a big generator that produces electricity, goes through a transformer and out to the grid. How much electricity? This system puts out a little over a megawatt, which is about enough to power 1,300 homes in Vermont. Another byproduct of this process, cleaner water. In the inside of here, these are packed with filters. Here, leftover particulate matter is removed from the water. There's really no contaminant left in the process after it's gone through the filter. The water then goes to the local community's water treatment plant. This is what it looks like that we're shipping out to the town. We remove over 99 percent of all the particles and contaminants in it. The digester also produces these phosphorus-rich solids. We call this a natural soil amendment. All of that phosphorus that comes into our plant from the concentrated food waste, we coagulate it with an iron salt and it makes this iron phosphate. We take it even to our house and put it in our garden. This is actually a useful product now for agriculture. Yeah, exactly. You can use this the same way you'd use manure or some other commercial fertilizer. It looks like compost. At Eric Roy's lab, they're studying the solids produced by the St. Albans Digester. Looking at how much of the essential nutrients for plants exist in this material and how that compares to more familiar materials for farmers. Farmers are familiar with manure, but this so-called digestate is relatively unknown. The goal is to try to produce useful fertilizers and also inform best practices for how to use it. Because if nutrients aren't used properly, they can run off to the water and cause environmental problems. In fact, helping the environment is a key reason Ben and Jerry's sends waste to the anaerobic digester. They want to lower that phosphorus pollution. Lake Champlain gets algae blooms a lot in the summer and that's due to phosphorus loading in waterways. And dairy inherently has phosphorus in it. And so we want to make sure that the phosphorus is not getting into the watershed. And by piping waste to the digester, Ben and Jerry's reduced its carbon footprint. We were sending over 600 trucks a year out on the highways going all across New England to dispose of this waste. So we're eliminating hundreds of trips there and back. But when it comes to the environment, the process isn't perfect. Even if it's greener than using landfills. For instance, converting that gas to energy still does release some air pollution. But here in Vermont, there's another reason to use an anaerobic digester. It is illegal right now in the state of Vermont to dispose of organic material like food waste, kitchen scraps, into a trash bin that will go to a landfill. Yeah, you know, enforcement's always a question with policies like this. But technically, everybody is legally required to send their food waste to some sort of processing strategy. Of course, anaerobic digestion isn't the only strategy. Many people compost their food waste. Roy's research on both is under peer review. We looked at what are the greenhouse gas reduction benefits associated with moving the U.S. more towards a Vermont-like policy where material goes to composting or anaerobic digestion. And it's well over an 80% reduction in greenhouse gas emissions from food waste management. Meanwhile, the rest of us can keep digesting Ben and Jerry's in our own way. For the PBS NewsHour, I'm William Brangham.