MANASSAS, Va. — The American recycling industry is in crisis — and cities are on the front lines.

The big picture: The economics undergirding the U.S. recycling system have fallen apart. Unable to absorb the extra cost, some cities are opting to kill recycling programs altogether — just as public concerns about climate change are ratcheting up.

China, the biggest buyer of U.S. recycled materials, has closed its doors. Before the ban, the U.S. was exporting around 70% of its waste to China.

Changing consumer behaviors have made the trash-sorting process more complex and expensive.

"The market for recycling has had a lot of shock," says Marian Chertow, a professor at Yale's School of Forestry & Environmental Studies. "Cities are thinking, 'Hm, is this really worth it?'"

How it works: A major recycling center in the Washington, D.C. suburbs used to turn a healthy profit from processing recycled materials from a 50-mile radius. Now it's having to pay vendors to truck material away, and is re-negotiating decades-old contracts with cities at higher rates — and explaining to consumers why they suddenly have to pay for curbside pick-up.

What we're seeing: Axios paid a visit to the center operated by Republic Services in the heart of Prince William County. It operates up to 22 hours a day to process about 550 tons of thrown out paper, plastic, aluminum and glass delivered there daily.

Despite the heavy machinery and increased automation involved, the process is still extremely dependent on humans.

On each shift, 28 "sorters" sift through the material as it rolls down a series of fast-moving conveyer belts. The workers spot and pull out non-recyclable trash from the stream so fast that they look like card dealers in a game of blackjack.

Contamination is a huge problem. People throw surprising things — Christmas trees, old carpet, shoes, diapers and even cinder blocks — into their recycling bins.

Manassas is not alone. Several other cities are struggling to make recycling work.

What's needed: Cities have to renegotiate their contracts with recycling providers, many of which are 30 years old, to find a viable business model, said Richard Coupland, VP of Municipal Services for Republic Services.

That includes charging consumers for curbside pickup of recycled materials. Now that consumers are convinced of the environmental value of recycling programs, most are willing to pay for them.

And cities have to shift from collecting as much recycled material as possible to only the items that have a market. "If there's no one in your local area to buy and recycle glass, you spend more fuel and carbon trucking it somewhere that does — and the benefit to the planet falls apart," Coupland said.

"There’s not a silver bullet— it’s going to take a number of factors. Reducing the waste stream, reusing more, rethinking how we’re packaging things, and education. What we've learned is that you can never stop trying to educate the public."

— St. Petersburg, Florida, Mayor Rick Kriseman

What to watch: "There's a huge opportunity for innovation within recycling," Chertow says. Researchers are looking at developing robots that can more accurately and efficiently complete some of the tedious — and even dangerous — tasks within large facilities, such as sorting.

Go deeper: Our plastic planet