Into High Gear

Material recovery facilities (MRFs) emerged onto the recycling scene as municipal recycling programs in the form of drop-off and then curbside collection spread across the United States in the 1980s and 1990s.

Their function initially was to store collected materials (most commonly newspapers, aluminum and steel cans, glass bottles and jars and plastic bottles and jugs) before feeding them to a baler to prepare them for outbound shipment.

For a number of reasons, the tasks taking place at MRFs have become increasingly complicated and are generally performed on a larger scale than they were at the outset.

A high-volume, heavily automated MRF in 2013 would be barely recognizable to the manager of a late 1980s recycling plant, whose last experience involved making a few bales per week of recyclables collected at source separated drop-off centers.

Freshman Mixers
As municipal recycling emerged in the 1980s, city- or county-run recycling drop-off centers were often set up with bins or bunkers designed to hold one commodity at a time. This source separation pattern could then be maintained at the processing plant to which the recyclables were hauled.

Curbside programs initially tried to maintain this same pattern, hitting the streets with collection trucks that contained several different compartments lining both sides of the vehicle. This system was a victim of recycling’s success to some degree.

As recycling programs spread geographically, added commodities and served educated residents eager to recycle, the tons available to be collected often overwhelmed the ability of compartmentalized trucks to cover a route. As they did, fuel costs and labor costs soared and route efficiency suffered.

Many of the haulers winning contracts to collect municipal recyclables had a solid waste background, and they proposed a solution drawn from their experience: allowing recyclables to be collected in a commingled fashion, potentially in the same style of packer truck that is used to collect residential garbage.

Two styles of collection competed in the 1990s and into the first decade of the new millennium. Dual-stream collection kept glass, metal and plastic containers separate from old newspapers (ONP) and other paper, while single-stream collection allowed all recyclables to be placed into a packer truck.

Both methods involved trading collection cost savings on the front end for greater operational costs later in the process. Single-stream collection in particular improved collection efficiency but required considerable investment in manual and automated sorting in the processing stage.

In the late 1990s and into the 2001-2010 decade, single stream gained municipal collection market share while consistently having detractors.

Paper mills decried the increasing presence of plastic, broken glass and flattened cans in their bales. Glass consumers were unhappy that not only was it difficult to get recycled glass cullet in one color but that contaminants were more common. Some plastic scrap consumers likewise expressed concern about their ability to receive a clean, non-commingled shipment.

The rise of single-stream, to a great extent, paralleled the rise of China as a massive importer of recycled paper and plastic. Fairly or unfairly, Chinese buyers gained a reputation of having a greater tolerance for shipments with more prohibitives and out-throws and then having the ability to deploy affordable labor to hand sort the material once it arrived.

MRF operators and equipment providers have defended the single-stream method and can demonstrate considerable investments made in the research and development of new technology designed to produce cleaner secondary raw materials.

In May 1992, Recycling Today featured a cover story on dirty MRFs, or facilities that separate recyclables from MSW.

Ready for the Big Screen
An October 1998 Recycling Today article prepared by MRF designer Nat Egosi of RRT Design and Construction, Melville, N.Y., and paper and recycling industry consultant Bill Moore, Moore & Associates, Atlanta, provides an overview of MRF automation being used at that time.

Automated single-stream processing was still in an early stage of its evolution, but the authors expressed little doubt it was where MRFs were heading. “Technological advances in the processing equipment have just begun,” they wrote, adding, “Hand-picking materials is the equivalent of digging ditches without bulldozers.”

Moore and Egosi predicted, as well, that MRFs would get larger in subsequent years. “Economy of scale is vitally important to the cost of processing,” wrote Egosi and Moore. “As time goes on, large processing facilities, handling material from larger areas, will evolve with lower per-ton costs.”

Egosi and Moore also provided a point of view that is repeated often regarding MRF operations. “One thing that appears to be missing with many processing facilities operating throughout the United States is viewing them as manufacturing facilities,” they wrote. “They are no different than any other operation that takes in a raw material and performs value-added functions to produce a finished product or commodity.”

This type of observation is often made when recycling advocates or buyers of scrap materials are worried that MRF operators with solid waste backgrounds may not always have the manufacturing concept foremost in mind.

The 1998 article then looks specifically at how clean grades of recovered fiber could be harvested from single-stream MRFs. “Single-stream recycling is dependent on technology to separate the incoming materials into marketable products,” they wrote. “Two types of equipment are integral to these processing operations: disc screens and incline sorting machines.”

The first role of disc screens, they noted, was to turn the single stream into a dual stream. “Specially designed disc screens operating with proprietary shaped discs separate paper from containers with over 90 percent efficiency,” they wrote.

Incline screens offered an alternative. “Inclined sorting machines are specially designed slanted conveyors with proprietary belt beaters that are able to sort paper from containers [also] with more than 90 percent efficiency.”

Egosi and Moore provide an overview of the three main fiber screen types, writting in part:

• Disc screens are ideally suited for automatically sorting paper. They work especially well in removing fines, grit and other small contaminants from a predominantly old corrugated containers (OCC) stream. However, there are limitations in the disc screen’s inability to sufficiently agitate the material to liberate (or shake out) the contaminants from the desired paper.
• Vibrating screens [have] the ability to efficiently separate materials into several sizes while not causing so much agitation that the material is “fluffed up,” meaning, the bulk density is significantly reduced. The disadvantages are similar to the disc screen, since some blinding does occur (though less with the vibrating screen).
• Trommel screens (or rotating-drum screens) agitate the material, giving undersized particles several chances to go through holes in the screen. The tilt, or declination, of the trommel (usually two to five degrees) helps material move from the upper end to the lower discharge end.

The article does not address the use of magnets, eddy currents and other machinery deployed to separate the container stream. These lines used significant automation then and have become more automated in the subsequent 15 years, with several optical sorting options available.

Screens are used in today’s MRFs to sort paper and to separate fiber from containers.

Back and Forth
As of the late 1990s, when Recycling Today published Egosi and Moore’s article, the merits of single-stream recycling were still being debated.

While most of the largest hauling and MRF operator companies invested in single-stream technology, not all parties in the recycling industry chain were convinced these were wise investments.

In 2003, San Francisco-based Conservatree issued a report critiquing single-stream collection and processing that included harsh comments from paper mill representatives contacted by report authors Susan Kinsella and Gerard Gleason. “Some of it might as well be backing a garbage truck up to the baler,” one newsprint mill buyer told Conservatree regarding bales from single-stream plants.

The presence of glass was singled out as the biggest source of trouble by many mill buyers, and their chorus of criticism may have led to glass being left out of some municipal collection programs in subsequent years.

Despite its critics, hauling companies across the country continued to migrate toward single-stream collection, particularly as fuel costs rose faster compared with processing costs.

On the processing side, equipment makers have continued to introduce new and upgraded products to help MRF operators keep labor costs in check and quality standards high.

The variety of screens has continued to increase, as has the performance of magnets and eddy currents deployed to create clean aluminum used beverage container (UBC) and steel food can grades.

Other advances have included optical sorting technology to identify types of plastic and associated air-jet or air-nozzle technologies to enact clean separation.

As technology has advanced, so has the presence of single-stream MRFs. A 2011 presentation by Richard Abramowitz of Waste Management Inc., Houston, showed the number of single-stream MRFs in operation rising from less than 10 in 1995 to about 85 in 2000 to 200 in 2009.

Figures are less readily available for the amount invested in MRF automation during the past 15 to 20 years, though in his presentation Abramovitz provides a figure of $7.5 million to equip the average single-stream MRF.

The dollars spent to equip 200 single-stream MRFs (and in many cases, reinvest in upgraded technology over time) have been considerable enough to spark healthy competition among equipment makers.

With processors and their customers continuing to seek more tonnage at improved quality levels, the level of investment seems likely to continue.