In the late 1980s, the city of Phoenix, Arizona made a bet: If residents no longer had to sort glass from paper from plastic, more of them would recycle. Single-stream recycling was born—one bin, one truck—and it spread fast. By 2010, nearly two-thirds of U.S. recycling programs had switched. Europe and Japan, however, didn’t follow suit; they opted for multiple bins and consumer sorting, betting that purity rather than convenience was the real prize.
Then came 2018. China upended the recycling world with the “National Sword,” a policy with an intimidating name that slammed the door on contaminated imports. Overnight, single-stream’s hidden costs became visible.
At first, it looked like the end of the debate between single stream and dual stream. But it turned out to be an inflection point. What followed has been a period of experimentation. Some materials recovery facilities are adapting, investing in optical sorters and robotics. A handful of cities have reversed course to dual-stream, reigniting the debate.
The stakes are far bigger than sorting logistics. The EPA estimates recycling a ton of mixed materials avoids nearly 2.8 metric tons of CO2-equivalent versus landfilling it. In 2018 alone, recycling and composting kept an estimated 193 million metric tons of CO2-equivalent out of the atmosphere—roughly the annual emissions of 42 million cars.
Contamination undermines this emissions math; convenience and greater participation shores it up. So what combination of technology, economics, and human behavior will bend the emissions curve further—now and in the future?
Source: Statista by CC
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The Climate Case for Single Stream
1. Quantity over quality. Contamination is single-stream’s Achilles heel—but it might be offset if more material is recycled. A number of municipalities that switched to single stream have reported increased collection rates ranging from 20% to as high as 84%. And if the numbers are right, this can translate into carbon savings. A 2022 life-cycle analysis paper focusing on Virginia found that single stream actually saved about 4% more carbon thanks to the higher participation rate.
2. Robots could sort it out. Single-stream recycling doesn’t ask people to sort their recycling, but that doesn’t mean the recycling doesn’t get sorted. It just happens at the collection center instead. AI-powered sorting robots equipped with cameras and trained to recognize and grab different types of plastic promise to make the process extraordinarily efficient. One manufacturer boasted their machines were able to help the facility hit a 99% purity rate and pick out as many as 55 items per minute.
3. Less trucks, lower emissions. Picture a recycling truck in a single-stream set-up, trundling through a neighborhood. By the time that truck has completed its route and gone down each and every street, it may have burned 100 miles worth of fuel. As Quartz pointed out, garbage trucks are basically the worst vehicle possible in terms of fuel efficiency. That may be bad enough, but since multi-stream set-ups often need multiple trucks to keep waste streams separate, they need to run that 100 miles several times to finish the job, increasing their emissions level well over the single-stream truck’s route. That said, electric trucks do exist and are starting to roll out. And since these don’t produce emissions themselves, the distinction may soon be moot.
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The Climate Case for Multi Stream
1. Quality over quantity. Multi-stream recycling turns out cleaner material. This is important since contaminated recycling often ends up in a landfill where paper and other organic material decomposes and emits methane and other greenhouse gases. U.S. landfills overall spew the equivalent of 24 million cars worth of emissions per year—and this might be a severe underestimate. High-end landfills do capture some of this methane, but most don’t. Refuse could also go into an incinerator to generate energy. But waste-to-energy schemes have been held back by high costs and big questions around how much they actually save in emissions. The BBC called them as bad as coal.
2. Less downcycling. So let’s say you throw a clear plastic PET bottle into a single-stream recycling bin. It is then mixed with all kinds of other plastic, and unfortunately once melted down, it can never be a drink bottle again. Instead, it’s turned into other, less valuable things like tote bags. That’s what’s known as downcycling. In terms of carbon, downcycling is better than a landfill. But it’s not that much better. One analysis put downcycling’s savings at only 4% compared to incineration (even in the best case waste-to-energy scenario), compared to 27% savings if it was same-cycled. And, as Grist pointed out, downcycling may ultimately be more about delaying landfill, not wholly preventing it. Multi-stream recycling, with its cleaner end products better avoids this problem.
3. Participation is an American problem. Single-stream schemes might seem to boost participation rates, but you know what else does? Being German. The EU as a whole, which mandates multi-stream recycling, enjoys an average municipal recycling rate of about 40%. Germany in particular hits a whopping 69%, thanks to very clear guidance on bin usage as well as pay-as-you-throw schemes, where households pay for garbage by weight, rather than a flat fee. Meanwhile, the single-stream-loving US lags behind at only about 32%.
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What to Keep An Eye On
1. Shipping and handling. Shipping raw materials can add significant emission costs and even cancel out the benefits of recycling. One report found that the emissions from truck transport outweigh the emissions benefits for recycled fiber after only 360 miles. Glass was better, at 1,150 miles, and metals could go upwards of 3,200 miles before their benefits petered out, but there was always a limit. Similarly, making a special trip in your car to return reusable containers to the store could end up producing more greenhouse gases than you save using the containers in the first place.
2. Better recycling through chemistry. Many plastics can’t really be recycled currently, no matter how they’re sorted. But new tech using advanced chemistry, enzymes, or even microbes might change that. Recently, for example, a team at Cambridge University built a solar reactor that turns old plastic bottles into clean hydrogen fuel. Another group of chemists in China developed a process to convert hard-to-recycle styrofoam waste into high quality jet fuel at a cost competitive with petroleum-based fuels. And still another lab announced a new chemical process transforms plastic waste into an effective carbon capture material. Many more such innovations are are making their way into commercial markets.
3. What’s powering the recycling plant? Recycling plants require energy to operate and where this energy comes from may end up mattering more than any of the material that actually passes through its doors. When researchers ran the numbers for paper recycling, for example, the results were sobering. If all wastepaper was recycled, emissions could increase by 10%. That’s because recycling paper uses more fossil fuel electricity than making new paper. The emissions would drastically go down if paper production and recycling were powered by renewable energy.“In our analysis,” they note, “landfill practices mattered more than material flows, and energy use mattered the most.”
