The Promise of MRF Technology

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When I was a kid watching the Apollo moon landings on our old black-and-white television, I was sure we would be vacationing on Mars by now, having all our work done by friendly robots, getting our meals in pill form, and traveling in our flying cars and personal jet packs. Though the future did not turn out nearly as cool as I thought it would be, it would be a mistake to assume that technological progress has stalled. Far from it. From the high tech to the mundane, advances in machinery, electronics, power systems, artificial intelligence, and a dozen other fields have transformed how we live and work.

While not as glamorous perhaps as a new phone app, recent advances in recycling technology over time will pay far greater dividends for our environment and our economy. From integrated systems to individual pieces of equipment, recycling has increased in quantity of output, efficiency of production, and quality of final product. While market demand greatly influences which materials get recycled, it is the technology of material separation and sorting that determines how costly and profitable these materials are.

The questions, then, are these: Can these increases in productivity and efficiency be maintained? Or will they flatten out in the future or even hit a wall where additional improvement are either not possible or cost effective? Will improvements in recycling technology meet a point of diminishing returns, or will they continue in an ever-upward spiral? Will changes in waste extraction methods alter the cost equation, making certain materials more profitable to recycle than others? What does the future hold?

Wastestream Characteristics
Municipal solid waste consists of a wide variety of materials, each with its unique physical characteristics, including size, shape, weight, moisture content, electromagnetic potential, and color. Each of these -characteristics determines how material is extracted from the wastestream during the recycling process. Market demand determines how it is reused, if it is extracted, and in what quantities. The following is a brief summary of MSW characteristics by waste category (USEPA 2012 data, rounded to the nearest percent):

The first category consists of organic waste. Strictly speaking, any waste material originating from plant and animal sources, such as office paper or woolen fibers, could be considered organic. However, this category includes yardwaste (grass clippings, leaves, garden waste) and foodwaste (from homes, grocery stores, food packaging plants, and restaurants), as well as wood from various sources. On average, yardwaste consists of approximately 13% of the total wastestream by weight, with foodwaste making up another 14% and wood at 7%, for a total of 34%. Combined, these constitute over one-third of the mass of municipal solid waste. Organic waste, however, is subject to significant regional and seasonal variations, in some areas doubling in quantity during the summer and fall seasons. The difference between organic waste and the rest of the wastestream is that it is compostable instead of directly recyclable. Many communities even ban yardwaste from the wastestream, requiring individuals and businesses to compost this material or else convert it into mulch. While yardwaste is relatively easy to prevent from entering the wastestream by means of separate bagging and disposal, foodwaste is a far more difficult material to segregate from the wastestream and nearly impossible to extract. If yardwaste can be prevented from entering the wastestream in the first place, foodwaste is often what is left at the end of the recycling process and forms a large portion of the unrecyclable residue that goes into landfills.

The second waste category consists of paper of all kinds (office paper, newsprint, magazine stock, corrugated cardboard) constitutes about 27%, over a quarter of municipal solid waste. This category includes a wide variety of material types and a wide diversity of shapes, sizes, and density. Depending on market demand, this material can be reused directly as pelletized fuel, indirectly as shredded packing and shipping material, or completely restored for reuse in its original form. The types of machines used for separating out paper products from the wastestream are as varied as the types of paper materials. Old corrugated cardboard (OCC) can be removed by disc screeners (a floor covered with rotating discs of different sizes and shapes that carry large light objects like OCC to the top of the wastestream for easy removal), while lighter papers can be extracted by air separators and the more precise air knives (blowers that use parallel sheets of high-pressure air blasts to minimize swirling and remixing of waste materials).

The third category, commercial plastics (HDPE, PVC, PET, etc.), makes up approximately one-eighth of the wastestream, or 12.5%. Plastic can be separated by type and ground down by a granulator for reuse as feedstock or scrim. And since it is made from fossil fuels, plastic also has a high BTU value, making it potentially useful as fuel.

The fourth category, ferrous and nonferrous metals, represents one of the waste materials more easily removed with one of the highest market values. Representing about 9% of a typical wastestream, ferrous metals can be extracted by magnets, while nonferrous metals can be removed by eddy-current separators.

The fifth category, glass of all colors (clear, amber, brown, clear), including ceramics, makes up about 5% of the wastestream. Glass and ceramics can be recycled by color sorters, thanks to the technology of light spectrophotometry (LSP). LSP can distinguish between values colors of commercial glass (clear, amber, brown, or green) as well as cullet and ceramics. A near-infrared sensor determines what the color is and triggers a puff of air from a blower that pushes the material into the appropriate sorting bin.

The sixth and last category is a mish-mash of miscellaneous materials (“other”) and clothing, including rubber, leather, and textiles, making up about 12% of household waste. This material tends to be difficult to recycle and consists of materials with marginal market value. So it usually constitutes the bulk of the residue remaining after an efficient recycling process and is usually sent to the landfill for final disposal.

Useful Products from Recycling, Today and Tomorrow
What materials get recycled the most today, and what can we expect in the future? Oddly enough, the most recycled product is not normally part of a typical wastestream. It is the lead acid battery, the kind used in most cars and trucks. These items are recycled at an exceptional 99% rate. This is the result of legal and regulatory mandates intended to keep toxic lead out of landfills where it could possibly impact ground water through leaks and surface water by runoff.

The most recycled material, asphalt pavement, is also not part of municipal solid waste. Again, 99% of asphalt is ground up and reused to fix and build pavement. This material has the unique property of being recyclable over and over again without loss of quality or strength characteristics. Furthermore, asphalt can include a wide variety of recycled materials (ground-up roof shingles, shredded tires, crushed glass, foundry sand, and chunks of slag).

Of the main wastestream, America generated 251 million tons of MSW and recycled almost 35%, or about 87 million tons (USEPA 2012 data). But after a sharp increase in recycling rates in the decade from 1985 to 1995, increases in recycling percentages have since flattened out somewhat, with little change since 2008. The total amount of MSW recycled in tons has followed this same trajectory.

The constituents of the recycled stream vary according to the state of various extraction technologies as well as by market demand. Of the amount recycled, organic waste makes up 27% (versus 34% of waste generated), paper and cardboard are 51% (compared to 27% of generated), plastics at 3% (compared to 13%), metals at 9% (with 9% of the amount generated as well), glass at 4% (5% of generated). Other items make up almost 6% of the amount of recycled materials (12% of generated) and are mostly bulk items like salvaged furniture or clothing.

These differences between percentage of waste generated and percentage of materials recycled provide a strong indication of which materials have the strongest market demand and the technology advanced enough to allow easier recycling. By the numbers, we can see that paper and cardboard lead all other recyclables, with a recycling percentage greater than its generation parentage. Metals come in second with matching recycling and generation percentages. Every other category shows lower percentages of recyclables compared to percentage of waste generated. Plastics come in last with only 3% of the amount recycled, compared with 13% of the waste generated.

So what can we infer from this data? Obviously, market demand and technology play major roles. Population density also has an impact. This is shown by the lower recycling rates achieve by sparsely populated states like Montana compared to those of densely populated states like Connecticut. In low population areas, the costs of transporting relatively small amounts of low-density, recycled materials over long distances to MRFs, and from MRFs to markets, negatively impacts the overall cost and marketability of recyclables. As such, while major cities may achieve recycling rates of 50% or more, rural areas have little economic incentive to recycle at all except for activities like composting of organic waste, which can be done completely at the local level. For this reason alone, which is outside the control of the recycling industry, it is doubtful that America as a whole will soon achieve recycling rates greater than 50%, let alone the often-stated goal of 100%.

Of all recycled materials, metals represent the easiest materials to extract from a wastestream and provide the highest prices per ton on the scrap market. Paper and cardboard are the next most popular recycled materials. Plastics come in last due to the difficulty of extracting and sorting out the myriad types of commercially used plastics.

But recycling is now an integral part of our manufacturing base. Over three-fourths of steel produced in the US is made from scrap iron instead of iron ore (Earth Policy Institute 2006). Over 90 million tons of scrap metal (worth more than $60 billion) is recycled in the US each year. Why? Because it is very cheap and profitable to do so. The electric arc furnace allows the production of steel from scrap with only one-third of the energy used to make steel from iron ore. Aluminum recycling is nearly as high with 51 billion tons recycled annually. The American scrap-metal recycling industry by itself is now a $65 billion nationwide industry employing 50,000 people and recycling 150 million tons of scrap materials annually (Institute of Scrap Recycling Industries 2008).

Paper recycling has had a proportional equal impact on the pulp and paper industry. In the past decade, American manufacturers have built 45 pulp and paper mills that utilize recycled paper as feedstock and only a few that use virgin wood exclusively. Again, it is because using recycled paper is a cheaper and more profitable way to increase the production of pulp. In neither case does the goal of environmental protection directly affect these business decisions. But the bottom line is positively impacted by environmental protection.

Unshuffling the Deck: Sorting and Separation Technologies
Are we anywhere near the limits of separation and recovery today, and what are the barriers to increasing recovery rates? When I watched Neil Armstrong walk on the moon, recycling (if it was done at all) was done by hand. This still occurs at “clean,” multistream MRFs, where presorted recyclables arrive for manual separation and stockpiling. The real technological advances have occurred at “dirty,” single-stream MRFs, where the operating equipment has been specialized for separation. There are nearly 600 operational MRFs in the US processing over 91,00 tons daily. Most of them are in high population density areas such as the North East Corridor and California. The technology they employ includes the following:

  • Magnetic separators extract ferrous metals from the wastestream as it moves past on a belt. These electromagnets can be set in an overhead position for direct removal, or underneath the belt, allowing the ferrous metal to stick to the belt while everything else falls off into a collection bin at the point where the belt moves past the last roller and turns under.
  • Eddy-current separators remove the nonferrous metals that magnets cannot. Using rapidly rotating magnets, eddy-current separators send an electric current into nonferrous metal objects, which in turn create their own magnetic field of opposite polarity. This repulsion pushes the metal off the belt and into a collection bin.
  • Disc screens are used to remove large but lightweight objects (such as cardboard). Basically, disc screens are large hoppers with floor beds lined with rotating disks of varying sizes, dimensions, and shapes (round, oval, star, etc.) whose edges are set perpendicular to the bed. As these disks rotate, the waste entering the screener is churned, and the resultant wave action carries the larger, lighter objects to the top for easy removal.
  • Rotating trommels (derived from machines used to separate slag from ore in mining operations) are used to remove small objects. These are rotating drums set at an angle whose walls have been perforated to allow small objects (fines, soil grit, shards, organics, and assorted residue) to escape from the main wastestream. The waste-stream is fed into the upper end. Thanks to gravity and rotation, only large objects that can be recycled emerge from the bottom end.
  • Air classifiers are basically large chimneystacks with a blower set at the top. Waste is fed into the classifier at the midpoint of the stack. The blower creates a suction that pulls lightweight paper up and out of the wastestream while heavy and large objects fall to the bottom. A cyclone separator can then further segregate paper grades by size and density.
  • Air knives are a refinement on the air separation technique. They use high-velocity sheet flows (in effect, “blades” of air) from blowers operating in parallel. This arrangement prevents remixing of the separated materials. Different air velocities allow for separation of objects of only slightly different densities, such as different grades of commercial paper, newsprint, and office paper.
  • Hydropulpers are another means of handling organic materials. More of a brute force method than the refined classifiers, these mechanical treatments and biological applications increase the density of absorbent materials in the wastestream. High-pressure streams of water crush and dissolve organic materials and paper, creating a wet organic residue that can be used as feedstock for anaerobic digesters.
  • Color separators allow for the separation of glass and plastics by color. Originally developed by the chemical industry to allow for automated sorting of chemical by color, LSP meters read the various wavelengths of light reflected off of glass and plastic and tell a blower to blast the object with a stream of air that will propel it into an awaiting -collection bin. A cousin to the LSP is the near infrared sensor, which can be used to judge the density (and therefore the type) of plastic waste object.
  • Humans beings are still an important part of MRF technology. Even the most advanced MRF relies heavily on manual labor. People are essential for the first step in any recycling process, the removal of nonrecyclables at the presort stage. Often it is more economical to remove odd and hard-to-define objects like odd-shaped plastics by hand sorting.

But that is today’s technology. What -additions or changes to sorting and separating technology can we expect to see in the future?

Automation and System Controls
How much more technologically advanced can recycling get? While we have achieved high levels of mechanization. But what about automation? On a scale of 1 (manually picked recycling) to 10 (a science fiction scenario with fully automated robots), where do we sit in terms of automation in recovery systems? Right now, we’re about at 5 and going higher.

Trends are definitely toward ever-increasing levels of sophistication of automation across all manufacturing and in all industries. There is an ongoing manufacturing renaissance occurring in America with industries returning from overseas (inshoring). But factories that used to employ thousands now only employ hundreds or dozens. “In the past decade, the flow of goods emerging from US factories has risen by about a third. Factory employment has fallen by roughly the same fraction.” (“Making It In America,” Atlantic Monthly January 2012). We can expect the same trends in the recycling industry.

The application of robotics and artificial intelligence in the recycling industry is still in its infancy. It will be more difficult to employ since, unlike other industries, there is nothing routine about the ever changing and unpredictable wastestream and its jumbled accumulation of various objects and materials. A European company, Zenrobotics is trying out a robotic arm designed to pick out different kinds of construction and demolition (C&D) debris at a facility owned by SITA Finland. C&D is a simpler wastestream than MSW, with fewer kinds of material and types of objects to sort through. But once this technique is perfected, it is only a matter of time before its application becomes widespread.

Will robots take away recycling jobs? Probably. But like all technological advances, they will create more jobs than they destroy. The job once performed by elevator operators was made obsolete by changing technology, yet nobody mourns its passing. Those who used to operate elevators are now in better and better paying jobs. So it will be with the position of waste sorter, whose job it is to pull out plastic shampoo bottles from a moving belt carrying MSW. Like those people who used to work the elevator controls, recycling workers will find newer and better employment.

Major Suppliers of Separation Equipment
Bulk Handling Systems (BHS) is a worldwide leader in the innovative design, engineering, manufacturing and installation of sorting systems for the solid waste, recycling, power generation, and C&D industries, among others. Clients around the globe choose BHS because of its experience, dedication to cutting-edge technology, quality construction and durability, and unmatched customer service. BHS has built some of the largest and most durable MRFs in the world, facilities that are achieving the highest throughput, recovery, and purity rates in the industry. BHS is unique in that it has united premium technologies-air separation from Nihot (Amsterdam), optical sorting from NRT (Nashville) and Anaerobic Digestion from Zero Waste Energy (ZWE) (Lafayette, CA)-to deliver integrated, best-in-class solutions. Whereas a dealer of equipment must rely on numerous manufacturers, BHS controls its technology and guarantees performance. BHS’s companies are truly integrated, collaborating from the design phase on to offer turnkey solutions that “close-the-loop” on recovery.

CP Manufacturing offers turnkey MRFs, equipment, design solutions, and after-sale service. The company provides whole recycling facilities complete with disc screens, trommel screens, conveyor belts, bag openers, magnetic separators, eddy-current separators, optical sorters, and balers. These systems are designed for “dirty” material, and single-stream MRFs that can efficiently separate glass, mixed plastic, nonferrous and ferrous metals, and fiber (OCC and mixed paper). Their capabilities include disc screens designed to separate 2D from 3D material efficiently, requiring low maintenance to maximize operating times and increase automation. The CPScreen is used to separate small paper products from larger cardboard, and flat paper from boxes. It comes with rubber cam-style discs arranged in assemblies of five, whose consistent spacing prevents jamming. It is operated by the CP Syncdrive, which uses carbon fiber timing belts rather than chains, so it has minimal maintenance needs. The CP NEWScreen is designed to separate larger fiber objects such as newsprint from mixed paper and small objects like grit and dirt debris. It uses long-lasting finger disc technology. And like the CPScreen, it features carbon fiber timing belts and has minimum maintenance requirements. The angles of the decks are hydraulically activated and electronically controlled, allowing for adjustments depending on the incoming wastestream. This allows for maximization of removal efficiency in any situation.

The Cirrus optical sorter from MSS Inc. combines high-resolution near infrared, color, and metal sorting. It allows users to sort a wide variety of such mixed materials as plastics, metal scrap, and cartons, using advanced digital signal processing and software algorithms. All CP MRFs and equipment are controlled with intelligent automation and supervisory control and data acquisition (SCADA) solutions for the operators to be able to most effectively operate their systems.

General Kinematics Corp. has developed an innovative line of vibratory screens called the SXS Screen. These high-stroke vibratory screens serve as an effective replacement for star screens, disc screens, and trommels. The key to their operation is the new side-by-side design. Another technological advancement is the double-stroke design that increases separation efficiency while using an energy-saving, low-horsepower drive. It is specifically designed for soft materials with low density that standard screens have trouble with. It can also be configured to process various types of materials. With low headroom requirements, the SXS Screen takes up less space, making for easy installation. Finally, it is custom-engineered to various widths and capacities for specific applications while being able to handle multiple streams (OCC, MSW, or C&D).

The Marathon Equipment Co. is a provider of a full range of solid waste recycling equipment, offering a line of separator equipment, debris screens, and sorting platforms. Both are included in the Marathon MRF System, a 10-ton-per-hour, single-stream waste and commercial processing system. In cooperation with Bulk Handling Systems and utilizing the proprietary Tri-Disk screening technology, the system includes the BHS OCC Separator, BHS Debris Roll Screen, BHS Polishing Screen, magnet, and eddy-current separators.

Bunting Magnetics manufactures magnetic cross-belt separators and eddy current magnetic separators. The magnetic cross-belt separators are positioned above the moving belt of the pick line. These magnetized belts run perpendicular to the pick line belt. The come in different sizes and strengths, but all are powerful enough to draw ferrous materials (cans, lids, tools, etc.) up and out of the wastestream. They can be customized to match the amounts of waste per minute, the width and speed of the pick line belt, and with the required elevation of the reach out. Productivity studies have shown that use of these magnetic cross-belt separators can reducing the staffing requirements of a standard pick line by two individuals, with nearly 100% effectiveness in ferrous metal extraction. The company’s eddy-current magnetic separators are equally effective in removing nonferrous metals. They are especially effective at extracting aluminum materials (soda cans, beer cans, pie pans, aluminum foil, pots, pans, etc.) from the wastestream. These are usually sized the same width as the pick line conveyor belt. They are usually run at 200 feet per minute, much faster than the conveyor belt. This is done to spread the material out for effective separation, improving the purity and quality of the final product.

The Dings Co. Magnetic Group manufactures eddy-current and magnetic separators alike. The company’s eddy-current separators range from the Model 9100, suitable for aluminum can recycling; the Model 9900, for electronic scrap metal processors and small particle processors; and the heavy-duty Model 9500, for auto shredding and high-volume MRFs. These are all equipped with rare-earth magnets that generate large and deep magnetic fields for increased non-ferrous metal recovery. Dings also provides self-cleaning, stationary, and severe-duty overhead electromagnets. The severe-duty model is suitable for recycling of concrete steel rebar.

The Eriez Manufacturing Co. is a supplier of multiple makes and models of magnetic separators. Always in the forefront of advances in recycling technology, Eriez has developed products for several new applications. For example, its new RevX-E eddy-current separator features an eccentric magnetic rotor. The eccentric motion increases the recovery rates of nonferrous metals in multiple industrial and waste applications. The eccentric design also reduces buildup of ferrous materials on the housing. It features a small-diameter magnetic rotor offset at the top of a large-shell enclosure. As a result, the repelling force of the rotors can focus on the point closest to the outer shell, increasing the rate of separation at this location. The positioning of its rare-earth magnet rotor can be adjusted for optimum removal with its focused magnetic field. The company’s Shred1 ballistic separator represents advancement in terms of traditional separators. A ballistic separator uses either one or a series of parallel floor sections that shake in opposition to each other, creating a wave motion that flings materials to separate collection. Set at an angle, it throws lighter objects to the top, while heavier objects settle at the bottom end. The Shred1 is specifically designed to provide high-grade ferrous material by efficiently separating iron-rich ferrous from a load of mixed metals and other wastes. It produces two distinct fractions: a premium shred with less that 0.2% copper content, and a traditional grade shred. Combination with its P-Rex Permanent Rare Earth magnetic drum creates Eriez’ CleanStream Process. The Eriez DensitySort recovers up to 70% of red metals (copper) and nonferrous fines and then sorts them into a light and heavy fraction. It combines controlled air blasts vibration and sloped floor to separate metals according to their specific gravities.

Machinex’s Mach series ballistic separators are designed to sort 2D materials (plastic, film, cardboard) from 3D materials (containers, plastic bottles). The motion of the ballistic separator carries the lighter 2D objects to the high end of the floor while the heavier 3D objects fall back to the low end. Fines fall through the bottom screen. This ability to handle multiple types of materials gives the Machinex Mach separators a high degree of versatility. But its main feature is its rugged durability. Its heavy-duty structure can support up to two stacked separator units, minimizing floor space requirements. Its variable speed drive is driven by heavy-duty bearings and shafts. The floor paddles are covered with abrasion-resistant steel screens and liners to minimize wear and tear.

Magnetic Products Inc. manufactures a wide variety of magnetic separators for industry applications, and eddy-current separators for MSW recycling. The main components of the company’s ES series are the rare earth magnets. These are the highest grade of permanent rare-earth magnet material. Using these materials ensures that it will apply a maximum magnetic field and never demagnetize. The separators come with optional ceramic coating on a fiberglass shell to resist wear and tear as the conveyor belt passes over the rotor.

Mini MRF LLC provides a complete system for the recovery of recyclable materials and can handle up to 35 tons per hour. The system consists of three separator modules. The first removes bulky items for disposal and large metal objects. The second removes small ferrous materials. And the last module handles multiple streams (scrap metal, UBC, PET plastic, and lightweight combustible materials). There are three types of optional modules that can be added to the main system to further refine the recovery effort. The fiber module recovers mixed paper or uses near-infrared sorting technology to further separate individual types of paper. The plastic module also uses NIR sorting to separate different kinds of plastics. And the EcoEngineered fuel module recovers combustible materials that can be used as a fuel source for the system itself.

The Steinert US eddy-current separator uses an eccentric pole system that prevents ferrous metals from adhering to the drum shell and a 30% increase in nonferrous metal recovery rates. The separators are available in three configurations for differing grain sizes and anticipated sorting requirements. It can handle aluminum particles as small as 5 mm (one-fifth of an inch) while being large enough to handle low-density materials at high volume throughput rates of 40 to 80 cubic meters per hour.

West Salem Machinery’s latest development is the massive Titan Trommel, which can handle an impressive 500 cubic yards per hour. Equally impressive is the variety of materials that this trommel can handle (asphalt shingles, woodwaste and bark, compost and foodwaste, glass, mulch, shredded plastic, and topsoil). The Titan is custom built for individual severe-duty applications, with an 8-foot diameter and lengths ranging from 20 feet (Model 820) to 63 feet (Model 863). It is not just its size that makes the Titan unique, it incorporates a series of unique design innovations: exclusive trommel ring assemblies, proprietary trunions, and dual-drum support wheels. Full covers allow access to multiple screen sections and making for easy maintenance, inspection, and replacement. Its severe duty structural steel frame is not just designed strong, its designed smart to minimize material accumulations.

Zimmer America Recycling Solutions (a division of ZARS–USA LLC) has formed a joint venture with Stadler Anlagenbau GmbH of Germany to create Stadler America LLC, the exclusive North American sales and distribution center for Stadler Anlagenbau GmbH. Together they bring to America one of Europe’s leading manufacturers of MSW recycling systems, lightweight packaging sorting systems, and sorting systems for single-stream waste. The heart of these systems is the ballistic separator. Stadler provides whole recycling systems (bag openers, trommels, magnet and eddy-current separators, and NIR plastic sorters, which are based on their patented stacked ballistic separators. Using the ballistic separator in the recycling system, segregating 2-D/flat (paper, cardboard, and films) and 3-D/rolling objects (containers, bottles), serves to simplify the overall process. The STT 2000 models are used to extract light packaging, all mixed paper, film, and hollow bodies, all separated into fines, flats, and rolling fractions. Each ballistic separator utilizes one set of paddles (6 paddles total) protected by Hardox plating and manufactured from 4-mm steel plate. The larger STT 5500 is designed to manage industrial wastestreams, MSW, and single-stream waste. Its heavy-duty frame construction uses 40-mm-thick steel plate with 10-mm-thick screen paddles. The specialized Model PPK sorts paper products and is capable of separating cardboard from mixed paper. With smaller screen perforations, it can further refine the separation process to separate newsprint.

And so we see these companies lead the recycling industry into the future with ever more advanced technology. It will mean more effective and efficient recycling, with fewer demands on our natural resources. It will raise our standard of living while protecting the environment.

That’s nearly as cool as having your own jet pack.

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