How MRFs are Adapting to the Modern Waste Stream
As technology changes our lives, so too it changes our trash, necessitating new methods and new equipment in order to process it. Until the processes and equipment can keep up, challenges and issues will plague the industry.
When’s the last time you had a phone book? “In 1993, the new phone book was a big deal,” says Steve Viny, CEO, Envisionwaste. Now, he says, that weight is gone and is never coming back.
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Today, electronic media is replacing printed media. The trend over the last 10 years is for less newspaper and mixed paper, and it’s due to the online phenomenon, according to Mark Neitzey, sales director for Van Dyk Recycling Solutions.
People want to read on a phone or tablet, Viny notes. The Sunday paper is not as thick. People don’t write letters, they do their banking online, and use PayPal. Even trade magazines are electronic now.
Mixed paper—paper and newsprint—is leaving the waste stream at “an alarming rate,” states John Green, president, Green Machine LLC. Replacing it as quickly as it’s departing is cardboard. In recent years, over 50% of recovered materials was newspaper; now it’s down to 20%.
Those numbers, however, vary across the country. All waste is local; socio-economic status factors determine what goes into the bin. While newsprint has declined 50 to 20% on the west coast,
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the amount still hovers at 40% in Florida, where the population skews older, according to Scott Jable, director of North American sales for Stadler.
Known in the industry as the “Amazon effect” because of the proliferation of online shoppers, corrugated cardboard has seen a major increase from residential accounts. Amazon Prime customers typically receive five items a month, most of which are packaged in cardboard. “[Cardboard] used to go from the stores to a commercial recycler and baler,” explains Neitzey. “Now it goes from homes to a MRF.”
OCC may be increasing, but it’s also 10 to 20% lighter than the old corrugated containers MRFs used to receive. Not only does this make it more of a challenge to mechanically separate, but it also means more volume is necessary to get the tonnage. “We used to talk on a per ton, per hour basis,” recalls Jable. “Now we need more volume.”
It’s not just paper and cardboard. PET bottles are also thinner and lighter. By using less material, they are cheaper to produce, but they pose challenges for recycling. Water bottles used to average 16 bottles to a pound, Neitzey calculates. Now it takes 38 bottles. He calls it “light-weighting” and says that bottles currently make up the biggest percentage of the stream.
Agreeing with his contemporaries, Charles Winum, recycling market manager for Steinert US LLC, says the big focus right now is on fiber—paper, corrugated cardboard, boxboard, and white offer paper—and plastics: in particular, #1, #2, and PET such as water bottles and milk jugs, which have a higher value relative to the price of oil. “Additionally, metals continue to be strong and account for 2 to 5% of inbound MRF material. Aluminum has the highest value right now because it is infinitely recyclable without losing its properties; it pays for itself.”
At $300 per ton, PET is still a good value; it’s just harder to get there. There are several reasons for that. Light-weighting is one, cross-contamination is another. Neitzey says a wider belt to get a single layer on the conveyor can alleviate some of the problem.
Sorting It Out
The quality of the separation of materials is key to their ultimate value, but it’s a tricky process. Cross-contamination is an issue, even in a drop-off system.
The problem is that quantity and quality are inversely related, creating tension. “Maximum throughput means the quality suffers,” says Viny. Better singularization is necessary. That is achieved by creating space between items: wider belts and faster speeds. But due to light-weighting, more material is being processed now than before and, therefore, the quality of the sort goes down.
Cross-contamination of mixed materials is difficult to overcome when packaging comes that way from the manufacturer. Blister packs, for example, mingle plastic with cardboard. “It’s difficult to deal with products like these,” states Viny. “In such an instance, the cross-contaminated material should be recovered for its calorific value or discarded.”
More manufacturers are blending the line between paper and plastic. Nick Davis, product design engineer and senior estimator, CP Group, calls it the “evolving ton.” It’s not the only challenging material. Flex packaging is also problematic. Flexible plastic package—re-sealable pouches—are often made of two or more materials. “The infrastructure is not set up for them.” However, he says there is an industry-backed push to make flex packaging recyclable. There’s also a pilot program to make K cups recyclable by putting them in a separate pouch.
One item that has become harder to deal with is the film bag. “They’re recyclable, but non-recyclable,” observes Neitzey. He estimates they run $500 per ton in processing costs, but there’s no market for them. Furthermore, it takes 53 to equal 1 pound.
Although film bags don’t usually get counted as input because there’s no separate category for them, 15 audits in Dallas revealed that they made up 5% of their inbound stream. Their system runs 35 tons an hour and can process 185,000 bags per hour or 35,000 pounds of bags per hour. However, the bags adversely affect the process because they get caught in the sorting equipment and generally take so much to recover, most MRFs consider them “not worth it.”
The problem is the end markets, Jable believes. “In Europe, bags are prized; they are washed and reused or used for fuel because they have a high BTU value.” It’s all economics, he laments. The plants have to make money to stay in business. “They want to recycle, but they rely on end markets.”
Glass is another problem, Jable adds, due to limited markets. Even worse, it causes a problem with the equipment. “It’s difficult to get out of the stream because paper goes with it.”
There have been many changes in the last five years. “We used to process three through seven,” says Jable, referring to plastics such as styrofoam, polypropylene, and yogurt cups. They relied on robotic sorting, concentrating on automating the “container side” of recovery of bottles, cans, PET, plastics #3 to #7, and metals. “But the market is poor, so we reprogrammed the optical sorting to remove just #5—polypropylene.”
Until recently, star screens were popular, but film gets wrapped around them. It’s dangerous, takes time to remove them, and is costly. And, Jable adds, the stars wear. “We use trommel and ballistic separators with paddles instead of stars. They’re used in Europe and can handle MSW.”
Packaging has changed, thanks in part to Amazon and plastics. Because so much of today’s packaging features mixed materials, Dick Reeves, director of resource recovery, General Kinematics Corporation, says there are no pure streams now; they are all contaminated streams—and contaminated streams often damage the equipment. That’s why many MRFs use vibratory sorters on the front end with optical sorters on the back end, he says.
Optical sorters work best on plastics and mixed paper, Winum believes. Optical sorters, which have a wider range in wavelength and can see materials better (especially white material like paper), make it quicker and easier for MRFs to separate materials, with higher recovery and purity rates, depending on their goals.
Separation is differentiated as 2D and 3D, Davis explains. Because plastics are becoming 2D, a mechanical separator is not efficient.
Optical sorters with air ejects are becoming more exacting and are now able to be trained to remove contaminants from fiber recycling streams. According to Green, this negative sorting practice increases material throughputs and increases the collection percentage of the desired products like paper, wood, plastics, and others.
Davis considers optical sorters as flexible, capable of “smart separation.” They lower volume capacity and are sensitive to surges. “Optical sorters can adapt to changes in the stream with greater adaptability.”
Optical sorting technology works well on aluminum, ferrous metals (soup cans), #1 plastics (PET), #2 plastics (milk jugs), #5 plastics (yogurt cups), mixed plastics, cardboard, and clean glass. But, Neitzey confesses, it still struggles to get paper clean. “MRFs spend most of their equipment, time, and energy to clean material that is going away. Half of all employees at a MRF clean up paper.”
To combat the problem of film bags getting caught on the equipment, Van Dyk Recycling Solutions developed a screen that doesn’t wrap with film: their non-wrapping 440 screen.
To enhance sorting capability, last year General Kinematics Corporation introduced FINGER-SCREEN 2.0 Vibratory Screen to replace older trommel technology. Suitable for MSW, C&I, and single stream applications, it can also separate lightweight, flexible materials. In fact, it a higher lift for challenging materials such as garbage bags, yard waste, and other lightweight, flexible materials. “Thin, flexible materials absorb energy,” says Reeves, “but the 2.0 throws materials better for great separation.”
The enhanced vibratory action spreads material across the deck for maximum utilization of the screen area, enabling continuous material flow to optimize separation. It separates materials based on 3D sizing with minimal blinding. Staggered fingers prevent material bypass and a unique cam-out surface helps eliminate catching and binding. Featuring a faster travel rate, its vibratory motion evenly spreads material for maximum classification efficiency.
Speed is important. Green says that robot arms are being tested in MRFs, but are too slow to be practical, although they are showing some promise in C&D applications.
However, speed can impede sorting if the belt isn’t wide enough for a single layer. “You need a single layer on a high-speed belt or the optical sorter won’t see the bottom layer,” explains Jable, even when using infrared cameras to separate.
Infrared technology is very sensitive, Viny notes. “Imaging is more sensitive. With belts that are 10 feet wide, it can sort materials up to 1,000 feet per minute.” In 1993, belts were one meter wide, he says. Now they need to be two-and-a-half meters wide to get good singulation. “An empty belt width gets better recovery because it reduces contamination and cross-contamination.”
Sorters at the Mid Valley Disposal MRF in Fresno, CA
Other separators commonly used at MRFs include vibratory feeders, which feed materials onto magnetic separation equipment and onto conveyor belts. With their heavy-duty construction, Brute Force Feeders and Electromagnetic Feeders are recommended for multiple applications, says Chris Ramsdell, product manager, Recycling Equipment, Eriez.
Magnets and Eddy Current Separators are more sensitive separators. Drum Magnets, Suspended Electromagnets, and AIP Magnetic Pulleys are used to recover ferrous metals, while an ECS separates aluminum cans and other nonferrous metals. Ramsdell refers to a recent test at a Florida MRF that indicated an ECS recovery rate in excess of 99% for used beverage cans.
“In spite of the improvement in recovery, MRF operators still know intuitively that they continue to miss metal as they watch potential profits go to the landfill. That’s where some waste recycling operations have installed the Metal Loss Monitor to help confirm those losses,” says Ramsdell. The MLM is typically positioned on the final waste stream in these facilities. It continually scans the residue stream for metal that has escaped the process and headed for landfill disposal.
Learning to Let Go . . . Or Not
“You can never have too many magnets,” says Viny. As Davis says, magnets were the earliest material separators and still have a place. Magnets can recover ferrous and nonferrous metals of less than one inch in diameter from the fines waste stream.
Permanent Deep Field Magnetic Drums are found in many MRF operations. Eriez models contain Rare Earth permanent magnets and bucking poles to project a deep magnetic field capable of removing ferrous from distances of up to 15 inches. The drum shell that contacts the ferrous material is made of heavy manganese steel and is abrasion-resistant for extended operating life.
An MSS fiberMax in operation
Drum feeders have been around for at least 11 years. Jable calls them a “metering device that provides a consistent feed for better sorting.”
Along with drum magnets, Winum says eddy currents are the workhorse of any MRF.
Screens also work hard. Reeves says that the popular rotary trommel is used by many as a primary screen, but it can be damaged by concrete. Instead, he suggests disc screens with rotating shafts.
Traditionally, trommel systems have been deployed at the front end of dirty MRFs and C&D plants to separate material streams into A and B streams, Green says. Green Machine developed a material sizing screen that out preforms trommel technologies. “These screens move higher tonnages, [enabling] the customer to adjust A&B material stream mix on the fly with greatly reduced wrappage. Far less space is required, units cost less, and maintenance costs are greatly reduced.”
For OCC, screens are still effective. Jable says sizing screens haven’t changed much since 1993. However, Viny says everything has been improved, including screens, sorting equipment, and magnets.
The only piece of equipment that hasn’t seen a lot of change is the baler. “A baler is still a baler,” says Viny.
A Single Idea
Single stream makes it easier for people to recycle; therefore, they will do it more than if they have to take the time to separate materials. In addition, for companies that offer it, Winum says it saves costs even if they have to separate more once the materials are all at the MRF because it requires only one truck for collection.
The single bin idea has been “kicked around” for a long time, Jable says, “but everyone has been afraid of losing fiber to the landfill.” However, he points out that Barcelona is capturing materials at a high percentage with the right equipment and the right configuration; contamination is less of a factor when things are done right. “There are lots of systems in the UK doing it.”
Here in the US, the single bin process is controversial, Reeves says. “It has yet to be proven.” Mixing good commodities with trash makes it hard to get a clean commodity at the end; most material is not recoverable due to the moisture content. “Some companies won’t take recycled paper and cardboard from those facilities. Pratt & Whitney doesn’t recommend using materials from trash.”
Mixed waste processing will be intriguing, Viny believes. Although it costs more to process the materials than to burn them, he says if you pull out the recyclables and organics, it may end up being more economical than making a second trip.
You have to start with the end product and work backward. Having an end market in mind can help justify the process. MRFs must remain flexible and open to new markets. “Companies want to recycle,” speculates Jable, “but they need end markets to blossom.”
Reeves mentions one MRF in Florida that pulled out 70 commodities from its waste stream. But some commodities are unwanted almost everywhere. Glass is an abundant mineral that has no value in recycling. Even worse, it is abrasive in the system. “It puts lots of wear and tear on the equipment and it embeds in paper and cardboard,” he says. “It’s a nuisance with few end markets that must be hand-separated.”
To get cleaner RDF, you want just paper and plastic, so you have to separate inserts, glass, stone, and organics. The traditional method of separation is to separate fiber from the container. In essence, these separations mean going from a single stream to a dual, Jable points out.
From a collection aspect, though, Davis believes we’re already there in most major and medium metropolitan areas. “Most cities have single stream. San Francisco, New York City, and West Palm Beach have dual stream. It’s historical practice; in those communities, they focus on commodity cleanliness rather than lowering costs.”
Plastics are often the drivers of single bin solutions due to the difficulties in dealing with a variety of plastics. The consequences of single bin, as Davis sees them, include the inability to get materials clean, yield loss, and contamination of fines. One other big consequence is the mixing of hazardous household items with heavy metals. Ultimately, he says, it “always come down to economics.”