Concrete Progress is an ongoing series of columns by Peter Brewitt devoted to exploring America’s infrastructure. It is part of Orion’s Reimagining Infrastructure project

Charlotte-Douglas International Airport, in Charlotte, North Carolina, saw 44 million passengers last year. That’s about twenty-three people per worm.

The worms in question, 1.9 million of them, live south of the airport, at CLT’s waste facility – the ragged legions of travelers making their way across the world do not see them. What those travelers do do is create trash. A big airport—Charlotte’s is one of the busiest in the world—produces a mountain of waste, from single-use water bottles to dirty tissues and much in between. At an average of 120,000 passengers a day, the airport represents the population of a city the size of Hartford, Connecticut, all eating takeout and wadding up paper towels.

I’ve been one of those passengers—Charlotte’s my closest big airport – and when I make my way between car and plane, I see a lot of public relations posters about how sustainable the airport is. I must say that I’ve suspected greenwashing. But when I looked into what CLT is really doing, I felt sheepish. It’s true: Charlotte uses a wide range of sustainable features, from low-flow water fixtures to a LEED-certified fire station. But the most impressive thing, to me, is that they use worms to turn their compost into soil.

Worm bins, as many readers probably know, are an increasingly popular means of home composting. Vermiposting, it’s called. You make a bin, give the worms some humidity, feed them waste, and wait as they turn food into what are known as castings (fresh, nutrient-rich dirt, essentially), which are much in demand from gardeners. Worm bins are efficient: you can use them in an apartment easily enough, and, if properly cared for, they do not smell.

Vermiposting at home is one thing, but employing worms to transform airport-scale waste is another. CLT churns out twenty-seven tons of waste a day, 70 percent of which is recyclable. The remaining portion that’s compostable—not just food, but bathroom waste and paper and leaves from potted plants—is broken down to manageable sizes and sent to the worms. CLT’s worm bin is 8,000 square feet and kept indoors, so as not to attract predators. The castings go to fertilize the airport’s landscaping. Nearly two-thirds of the airport’s waste is now diverted from the landfill.

I should note, though, that the business side of keeping worms has not been without difficulty. The airport has had some conflicts with the company that started running the facility, and there have been cost and machinery problems. But this does not change the system, or its benefits, which include using castings instead of landscape fertilizer and saving on landfill costs.

Driving by CLT not long ago, I thought of how amazing flying is—if our ancestors saw a 747 roar across the sky, it would have blown their minds. It is an eternal dream of humanity realized, and a crucial part of our infrastructure. But it’s easy to forget the ecological impact of airports, and hard to know how to take individual responsibility for it. As a result, it’s often up to airports themselves to address the issue.

There’s great reading available on Charlotte’s innovations: from the company that runs the worm program, from the airport itself, and from the local business journal. Information on worm bins are all over the web.

Peter Brewitt has wondered about infrastructure ever since a flood kept him away from three days of kindergarten. A professor of environmental studies at Wofford College, he is devoted to understanding how people decide to restore and remake their environments.