Modern industry has made great strides in turning trash into tomorrow’s new products, but the process is still a long way from perfect. New technologies can help. Plus, updates on chemical recycling, design for recycling and dirty recycling.
If your neighborhood is like most locales in the United States, there’s a thing that’s hard to unsee once you notice: The trucks that empty your blue recycling bin look just like the trucks that collect your trash.
So – they are taking your stuff to be recycled, right? The trucks aren’t just loading up all those carefully separated newspapers, cardboard boxes, metal cans, plastic bottles and glass jars, and dumping them along with the rest of the garbage?
Rest easy. Your recyclables are (probably) winding up exactly where they’re supposed to go. Same trucks, different destination — most often a sorting plant much like the materials recovery facility (MRF, pronounced “murf”) that Michael Taylor is explaining right now.
“Our facility serves 2.6 million people,” says Taylor, raising his voice over the din of conveyor belts, blowers and separation screens moving multiple streams of sorted recyclables through a space the size of a football field. That works out to an average of nearly 1,000 tons per day — a round-the-clock flow of material pouring in from curbside bins across metropolitan Baltimore, the District of Columbia and most of the suburbs in between.
That also makes this MRF in Elkridge, Maryland, one of the busiest in the United States, says Taylor, who runs it for the facility’s owner, Houston-based recycling giant Waste Management. But other than that, it’s pretty typical of the hundreds of other MRFs around the country. “We are a hardcore manufacturer, except we do it in reverse,” says Taylor. “We’re taking this mixed-up stream of material and we’re de-manufacturing it, breaking it down into individual components.” In the same way that Ford or Chevrolet builds cars, he says, “I’m building bales of newspaper, bales of aluminum cans, bales of PET water and soda bottles.” Indeed, this is the fundamental business model for Waste Management’s MRFs and many others: Charge cities for the cost of collecting and sorting recyclables, then share with them any profit the MRF makes from selling the sorted bales to recycling mills. These mills are the firms that will actually turn the stuff into raw materials for brand-new bags, boxes, fleece jackets, shoes and more.
But that last step is also where the story gets messy. This isn’t so much because of the coronavirus pandemic: Most US cities (although by no means all) are trying to maintain curbside recycling as an essential service. If anything, the quantity of residential recyclables has mushroomed as people stay home.
No, what’s hit recycling hard is that roughly a third of the bales coming out of this MRF and others like it used to go to recycling mills in China and other countries. But in July 2017, the Chinese government announced that its plants would quit accepting “contaminated” material from outsiders — contamination being, say, the residual paper, glass and metal that never got completely separated from a bale of plastics. Part of a larger initiative known as National Sword, the policy stated that China would drop the allowable fraction of contaminants from 5 percent or even 10 percent down to 0.5 percent, effective March 1, 2018.
Since 0.5 percent was a standard that was much more expensive for MRFs to meet — if they could do it at all — the year that followed saw their carefully sorted bales of recyclables glut the market. This led to steep drops in prices and a lot less money flowing back to the cities through those profit-sharing arrangements. Dozens of cities responded by suspending curbside pickup, and the media began to run dire headlines like “The World’s Recycling Is in Chaos.”
Things have now stabilized a bit. The Elkridge MRF, like many others, has tried to meet the new standard by slowing down its sorting lines and adding more people. But the recycling industry in much of the developed world is still like an ecosystem just beginning to recover from a devastating wildfire. The good news is that what’s coming back is an industry that has been forced to rethink and reinvent itself.
Within the MRFs, for example, the shock of National Sword has accelerated the deployment of robots, computer-vision systems and other new technologies to improve sorting and reduce contamination. And downstream, dozens of new recycling plants are being built to process the MRFs’ output here in North America. Some of these new plants are expected to use advanced technologies such as “chemical recycling” — an emerging approach that could go a long way toward recapturing the 90 percent of plastics that currently aren’t recycled in the United States and Canada, and instead end up in landfills or the environment (see Solving the growing plastics waste puzzle).
That makes for a lot of change all at once. But change is a constant in this business. “It’s not exactly what I went to school for,” says Taylor, who has degrees in public administration and political science. “But every day is a different day.”
On the tipping floor
Central to any notion of long-term sustainability is the dream of a “circular economy” — one in which factories wouldn’t just feed a linear pipeline from mine to landfill, but instead would use today’s products as raw material for tomorrow’s.
The modern recycling industry is where that dream meets reality — which, here at the Elkridge MRF, starts on the tipping floor. This is a big open space where the collection trucks take turns backing in and dumping the contents of your blue bin and many others on top of the previous truck’s load. In between tips, a front-end loader methodically scoops up big chunks of the pile and deposits the material on a conveyor belt, which carries it up to a pre-sorting area where workers are lined up on both sides.
The workers are all wearing yellow vests, masks and heavy gloves, but not just for Covid-19. Their job — and it’s a filthy, dangerous, smelly one — is to pick out all the items that rightfully belong in a landfill or incinerator: Dirty diapers. Garden hoses. Old clothes. Used hypodermic needles. Dead cats. Bowling balls. Filmy plastic bags that will tangle in the sorting machines. Cartons of sour milk that will foul everything they touch once the containers inevitably burst open down the line.
“Our top three challenges are contamination, contamination and contamination,” says Taylor — stuff that never should have come anywhere near a blue bin. Among the worst offenders are the rechargeable lithium-ion batteries found in just about every electronic gadget on the planet. They can be recycled, says Taylor, “but not in this setting” — mainly because they contain acid and other volatile chemicals. “You run over the battery with a loader, or crush it in one of the machines, and it could spark, short out and cause a fire in the cardboard.” Likewise with half-full propane tanks, or aerosol spray cans. The people at his MRF have to put out fires maybe once per month, says Taylor — “too frequent in a plant that’s handling paper.” (In 2019, outside of Phoenix, a MRF operated by the waste management firm Republic Services was destroyed by such a fire.)
The need for this pre-sorting step might seem like a measure of recycling’s many shortcomings — and it is. But it’s also a testament to how far recycling has come. Fifty years ago you wouldn’t have seen any trucks queueing up outside, because MRFs didn’t exist. Instead, garbage trucks would have been taking everything they collected straight to the local dump — likely some unregulated piece of land where toxic smoke billowed from trash fires, asbestos and lead paint chips blew freely in the wind, and anything could leach into the groundwater.
That situation didn’t change until the 1960s, 1970s and 1980s, when concerns over public health and safety led Congress to enact a series of increasingly stringent regulations on waste disposal. One major landmark in this process was the Resource Conservation and Recovery Act of 1976, which covered not just ordinary trash, but also the safe disposal of chemicals and other hazardous wastes. “RCRA is what established the modern landfill, with linings, standards for different types of waste, and all the rest,” says Bradley Kelley, an engineer with the waste-management consulting firm Gershman, Brickner & Bratton, Inc., in McLean, Virginia. Since this was expensive, cities started looking for ways to divert trash from the landfill, keep their costs down and potentially recover some valuable materials, such as metals.
One result, beginning in 1980, was the first generation of curbside recycling programs. By today’s standards they were pretty basic, says Pete Keller, a vice president at Republic Services. Because there was still no way to do centralized sorting, for example, “it was common for companies like us, or municipalities, to provide these little 18-gallon bins” — the ones that are about the size of a laundry basket. Customers were then supposed to separate everything at home: paper in one bin, glass in another, cans in a third, and so on. The bins would then be picked up by a special truck with separate compartments for each category.
In some ways this “multi-stream” approach was ideal, says Keller, because the consumer-separated material was very clean: “You basically would dump each compartment on the floor, and run that through a baler ready for market.” That’s why a few cities still use multi-stream recycling even now.
But for most municipalities, says Keller, multi-stream wasn’t really sustainable. One reason was cost: Cities not only had to invest in special trucks with multiple compartments, but also had to ask the drivers to hop out at each stop, lift each bin and empty it into the right compartment by hand. The process was slow, clumsy and expensive, not to mention being a recipe for workers’ repetitive-stress injury.
Another reason was that, as Keller puts it, “our customers wanted easier solutions.” Sorting stuff into all those bins was a pain, and participation in recycling was dismal through most of the 1980s — diverted trash made up no more than 10 percent of all municipal solid waste.
And then in 1991, after gathering the increasingly dire evidence on risks and health effects of existing dumps for more than a decade, the Environmental Protection Agency finally issued its RCRA regulations on municipal solid waste. In the decade that followed, says Keller, the number of operating landfills in the United States fell from more than 6,300 to under 2,000. “Cities and counties could no longer afford to run those sites the way they had historically run them,” he says. The shift gave cities an even more powerful incentive to get those recycling numbers up.
Thus the move to “single-stream” recycling, in which consumers could forget about the basket-sized tubs and instead toss all their recyclables into one bin — typically, a much larger blue model with wheels. Thanks to the parallel growth of MRFs to centralize the sorting, says Keller, this is how most US recycling programs have operated since the 1990s. Single-stream has slashed collection costs, since cities can now use the same trucks that pick up the regular garbage bins. And it has greatly improved recycling rates, with many more households participating and many more “pounds per put-out” in each bin.
“Generally when we convert over to single-stream,” says Keller, “we see a 200 to 300 percent increase in the amount of material we collect” — one big reason why recycling rates today are about 35 percent of all municipal solid waste. Along with a parallel rise in waste-to-energy incinerators, as well as the industrial-scale composting of food, yard waste and other organics, these improved recycling rates have helped keep the total tonnage of waste going to US landfills nearly flat over the past two decades despite an almost 20 percent growth in population.
Yet the move to single-stream had its own downside: the contamination that is all too apparent on the tipping floor at Elkridge and every other MRF. Think of it as “aspirational recycling,” says David Biderman, executive director of the field’s leading professional organization, the Solid Waste Association of North America. “When we tell people to just throw all the metal or all the plastic into a recycling bin,” he says, “they’ll say, ‘Well, this is a hose and it’s made out of plastic and metal. So if I put it in there, they’ll figure out how to recycle it.’” (Nope: Garden hoses, electric cords and the like will tangle in the sorting machines and bring the whole MRF to a halt.) “Or they might say, ‘My gun is made out of metal, so I’ll put that in the recycling bin ’cause I don’t know how to get rid of it.’” (Sometimes the guns are loaded.)
Still, says Biderman, the contamination problems highlighted by National Sword are forcing municipalities to get serious about educating consumers as to what does and does not go in the bin. “I think we got a little lazy there,” he says. The new efforts are already having a measurable effect. In January, Waste Management reported that the average contamination rate for material coming into its MRFs had fallen from 24 percent to 18 percent — “still not a number to be totally proud of,” says Biderman, but a sign of real progress.
And there is room for a lot more. In 2017, for example, an industry-funded nonprofit group known as the Recycling Partnership pioneered an education program that gives consumers immediate feedback. On pickup day, crew members will walk ahead of the truck peeking into each blue bin. And if they see something that shouldn’t be there — plastic bags, a hose, a deer carcass — they will leave a friendly “oops tag” explaining the problem. “Next time,” the tag adds, “we won’t be able to collect your cart if we see these items.”
Pilot programs in Atlanta, Chicago and Denver have since expanded to many other cities, spurred in part by grants from the Recycling Partnership. Another boost came when Massachusetts incorporated the oops tag idea into an open-source Recycling IQ Kit that is free to anyone who wants it. This feedback works impressively well, says Biderman: Most people will do the right thing if they just know what it is. “Cart rejections in the communities that use the Recycling IQ Kit have declined by up to 70 percent,” he says. True, he adds, oops tags and the like are still the exception rather than the rule. “But part of our goal is to scale these best practices and get them into the hands of everybody.”
In the MRF
Everything that comes off the Elkridge tipping floor and makes it through the pre-sorting process rides a conveyor belt into the MRF proper. Discarded bottles, boxes, papers, cans — the stream is oddly hypnotic to watch, and can reveal a lot about the society it comes from. For example, says Taylor, “this facility was built in 2006, and 80 percent of what we received back then was newspaper.” Today the fraction is less than 50 percent, which reflects the shift from print to online news. Those same years have seen a surge of cardboard boxes, courtesy of Amazon and the rise of e-commerce. And likewise, glass jars and metal cans have given way to a lot more plastic than there used to be — water bottles, milk jugs, blister packs and more. (See Design for Recycling.)
From the MRF perspective, of course, easily the most seismic change was the 1990s move to single-stream reprocessing, which is why these facilities exist at all. The first plants designed to sort mixed content on a large scale date back to the early 1990s. MRFs and single-stream recycling have grown up together ever since. Today the United States has more than 300 of them.
Fueling that growth have been two major innovations — the first of which, the 2-D/3-D separator or “disk screen,” is also the first thing the incoming stream encounters as it enters the MRF. The screen is basically a series of rollers with spaces in between. As the conveyor belt pushes material onto the rollers, wide things like flattened cardboard boxes will ride across the top to be picked up on the other side. But compact, “3-D” things like cans, jars, bottles and paper will fall through the spaces onto another conveyor belt, which takes them to a second screen equipped with blowers to extract the paper. Neither separation is perfect, of course, so still more conveyor belts carry both the cardboard and paper streams past rows of workers doing quality control, which means picking out extraneous plastic, glass and the like before the materials are sent for bailing.
With the paper and cardboard removed, the belt carries the remaining material on to the next step, which is to extract metal and glass. This part of the process isn’t visible at Elkridge, since everything is enclosed for safety. It’s an application of techniques that the scrap metal industry perfected ages ago. First, an electromagnet pulls out anything made of steel, like those “tin” cans from the grocery store. Then an “eddy current generator” hits the stream with a rotating magnetic field, which kicks aluminum cans and other non-ferrous metals into collection bins. And in between, the stream passes over another screen that allows the glass to fall out. (It will eventually get crushed into “cullet,” an easy-to-ship form.)
That leaves the plastics. The challenge here is that plastic items don’t have much economic value for recycling until they’re sorted by polymer type — and there are more than a dozen types in widespread use. The solution is the second major innovation in MRF technology, the optical sorter. Despite the name, Taylor says that current-generation sorters use infrared light, which allows them to identify the polymer type of, say, a water bottle by monitoring how those infrared wavelengths are reflected. The machine will then use a jet of air to blow that item into the correct bin.
Elkridge’s scanner system was retrofitted after the plant was built, says Taylor; the technology is that new. And it was upgraded again in May 2020. “But it’s always been fast,” he says, nimbly extracting items made of PET — polyethylene terephthalate, denoted by the numeral 1 inside the recycling symbol — and HDPE: high-density polyethylene, denoted by the numeral 2.
Unfortunately, Taylor adds, those two plastics are the only ones recovered at Elkridge — partly because they’re the most common and most profitable, but also because he’s running one of the busiest MRFs in the country in one of the smallest buildings. Like many other MRFs in the eastern United States, where the cost of land is high and space is tight, this one has been crammed full of machinery from day one. He’d love to be pulling out polypropylene (number 5), as well, says Taylor. “But I don’t have any bin space to store it before I get it to a baler.” So everything that’s not PET or HDPE gets shipped out to the recycling mills in bales of low-value mixed plastic.
Space-constrained or not, however, Taylor and everyone else in the industry is keeping a close watch on a new generation of MRF innovations now in the pipeline. (See One bin future: How mixing trash and recycling can work.)
On the high-tech end, for example, MRF operators are increasingly investing in industrial robots for the pre-sort and quality-control steps. These robots don’t look anything like C-3PO, or even R2-D2. They’re more like suction cups suspended over the moving conveyor belt. But with the help of high-end computer-vision systems, the cups can dart down, pick up individual items very precisely, and drop them into the appropriate bins. This makes them faster and more accurate than people at picking extraneous items out of the stream — and thus keeping them out of the bales. It hasn’t yet been feasible to retrofit robots into older plants like Elkridge, says Taylor, although that remains a possibility for the future. “But our newer plants are being equipped with AI-based robotics as we speak.”
Computer-vision systems are also transforming optical sorters, says Republic Services’ Keller. The newer optical scanners combine existing infrared technology with high-speed digital cameras that work in the visual spectrum, and that can identify items using artificial-intelligence-based image recognition techniques. “The thing that’s interesting to us is that visual recognition is a lot more adaptable,” says Keller. “It can recognize many more forms, and many more types of materials” — say, flattened water bottles that are so light that the disk screens sort them into the paper stream, or jars with plastic shrink-wrap labels that the infrared scanner by itself would have classified as solid PET. Again, he says, the payoff is much cleaner bales.
At the shipping dock
Whether it’s sorted by high-tech or current tech, a MRF’s output will be something very much like the chest-high, multicolored bales of plastic, paper and such now waiting in the Elkridge shipping area.
Back in the 1990s, if this facility had been around then, these bales would have been trucked off for conversion into new products at mills all across North America. But that was before globalization and the rise of China, says Mike Crang, a geographer at Durham University in the UK and coauthor of a study on the global recycling economy in the Annual Review of Environment and Resources. As more and more manufacturing shifted out of the US, he explains, “the physical manifestation of trade imbalances was empty shipping containers piling up in the West.” So rather than just sending them back empty, Chinese buyers started packing them with bales of recyclables that plants in their country could then turn back into even more products to ship to Western consumers.
As a result, by the time the Elkridge MRF was built in 2006, many North American recycling mills had been mothballed. That’s one reason the MRF’s owner, Waste Management, picked this site in the first place: Once the bales were packed into container trucks, it would be just a quick drive from Elkridge to freighters waiting in the Port of Baltimore.
“But as we became increasingly reliant on those overseas markets, it ended up being a bit of a devil’s bargain,” says Dylan de Thomas, a vice president at the Recycling Partnership. With Chinese buyers apparently willing to accept anything, and Western consumers tossing more and more of the wrong stuff into their bins, the MRF side of the industry had little economic incentive to keep the quality up. “The joke in the industry used to be that China always had the most stringent environmental laws on the books — they just never enforced them,” says de Thomas.
Until suddenly, they did. The announcement of National Sword in 2017 “was a powerful signal that really reset the industry,” says de Thomas. Still, he says, the plummeting market for sorted paper and plastics has had a silver lining: “You’re seeing a massive amount of investment into new, retooled or reopened mills here in North America.” His group has counted up some $4.7 billion being invested in new or reopened plants, divided between those recycling paper and/or cardboard, and those recycling plastics.
And if they succeed? Then Michael Taylor and his fellow MRF operators will be happy to have new markets for their bales of sorted plastic. In the 27 years he’s worked in this field, says Taylor, one thing that’s never changed is his belief that recycling is absolutely worthwhile.
“Over time,” he says, “it’s good for the environment, it’s good from a carbon footprint perspective. And it’s why we do what we do.”