The recycling process: how a materials recovery facility works

Once you haul your recyclables out to the curb, what happens to them? A lot of the recycling process depends on your municipality’s practices. Most rely on single-stream recycling. That is, they require households and businesses to separate commingled recyclables from trash. Recycling goes to a materials recovery facility (MRF, often pronounced “murf”). 

Dual-stream recycling programs require households and businesses to further divide recyclables into two categories. Usually, it means separating paper from metal, glass, and plastic. I have heard of places in Europe that require still more rigorous source separation. But I can’t think of any in the US.

Both of these methods produce a higher quality output, but fewer people are willing to participate. So single-stream recycling has become the norm. 

Clean vs dirty MRFs

Ordinarily, sorting recyclables takes place at a materials recovery facility. Some places offer drop-off centers where patrons take their recyclables and sort them into different bins. That kind of manual sorting results in a much cleaner and more valuable product.

Single-stream MRFs have long been divided into two categories: clean and dirty.

In a clean MRF system, the recyclables go to a materials recovery facility and the trash goes to the landfill, or perhaps an incinerator or waste-to-energy plant. What goes through the recycling system includes no trash except what results from someone’s carelessness at home or at work.

On the other hand, a dirty MRF, also called mixed waste processing (MWP), accepts unsorted waste. That is, households and businesses do not separate recyclables from other trash. The facility’s machinery and personnel do all of that. There is no need—and no possibility—to educate anyone about the recycling process. What’s more, the unsorted trash poses greater health risks for workers.

Where a clean MRF can process and sell more than 90% of the material that lands on its tipping floor, a dirty MRF can barely manage half that. And it can’t recover any clean paper or cardboard.

Fewer than 5% of all American MRFs use this method. It seems like a good idea to collocate MWP facilities with landfills. Some of their output could then go through the MRF process and divert more recyclables from landfills. MWP does not seem workable as a town’s sole recycling technology. 

One example of a dirty materials recovery facility

Montgomery, Alabama opened a new MRF in 2014 designed to remove recyclables from unsorted waste and operated by a company called Infinitus (IREP). It claimed to be the latest state of the art recycling facility.

Infinitus cast a wide net to get enough trash to make its business model work. It contracted to collect trash from cities as far away as the Florida Panhandle. It made money for a while, but when commodity prices plummeted, it had to cease operating in 2015. All the towns it collected from lost the ability to recycle until they could build their own standard clean MRFs.

Santa Rosa County, Florida, for example, opened its new MRF a year after Montgomery’s closed. Montgomery had no recycling until 2019. For some reason, the city seems bound and determined to continue with MWP. It hired RePower South to update and reopen the plant. RePower South started operation in early in 2019 at no charge to the city. It  opened with 45 employees.

RePower South’s business model differs from Infinitus’ in two significant ways. It converts organic wastes that it can’t recycle into a fuel that power plants can burn instead of coal.  Also, it opened a drop-off center in front of its facility where people can separate recyclables into different kinds of paper, metal, and plastic. 

It costs $50 for RePower South to process one ton of trash. The company can only make $35 selling it. So in August 2020, it had to ask the city council for a recycling fee of $2 per month per customer. By that time, its workforce had shrunk to 39 employees.

If plant works out this time, it will extend the life of Montgomery’s landfill by 75 years. Whatever the city will have to pay for operating it pales in comparison to the cost of building new landfills. But will it?

Sorting recyclables at a clean materials recovery facility

 

The following description is based on a tour of the materials recovery facility in Greensboro, North Carolina in 2017. Other MRFs may use more or less automation and do some of the steps in a different order.

The tipping floor has separate areas for household and commercial recyclables. Commercial recyclables tend to have a higher concentration of  valuable office paper and cardboard. Residential recyclables contain more food waste contamination. Mixing the two could contaminate clean paper from the commercial accounts.

Presort

A front loader pushes material from one or the other pile to a hopper, where it lands on the first of many conveyor belts. The presort workers on each side of it remove what can’t go through the system. Scrap metal and tanglers that would damage the equipment if not removed. And Styrofoam will break into little pieces and contaminate everything else in the system.

Tanglers include plastic bags, coat hangers, hoses, extension cords and anything else that can get caught in the rotating equipment. 

The presort line may also remove recyclables that just can’t go through the system. For example, shredded paper can be recycled. It just can’t go loose in the recycling container or it will get lost in the system. So the proper way to recycle it is to put it in a clear plastic bag—the only plastic bag that you can ever put in recycling. The presort people will remove bags of shredded paper and set them aside. 

Presort workers also remove buckets, broken play sets, and other recyclable plastic too large to go through the equipment. These items get carried to their proper place at the end of the machinery.

Mechanical separation

The first step in sorting is to separate two-dimensional objects (paper, cardboard, etc.) from three-dimensional objects (bottles, cans, and jars). Rotating screens push the lighter two-dimensional material upward to a conveyor belt. Gravity pushes the three-dimensional objects downward to another conveyor belt.

On the two-dimensional side, other screens separate office paper, newsprint, chipboard, and cardboard. Each material has a different density and therefore reacts differently to the screens.

On the three-dimensional side, the glass falls out of the system onto a concrete floor, where it breaks.  A magnet captures steel cans, and an eddy current sends aluminum cans in another direction. 

Optical scanners distinguish the different kinds of plastic and send them in different directions with a puff of air. Like different kinds of paper, the system distinguishes different kinds of plastic by density. Greensboro’s system separates PET (no. 1) and HDPE (no. 2) and leaves the rest as mixed plastic. 

Other MRFs may perform these steps in a different order, their machinery works on the same principles. At the end, everything the system separates goes to its  own conveyor belt and gets dumped in an appropriate bin.

Human sorting

After the machines finish the rough sorting, humans remove certain materials from each belt. For example, some of them separate colored HDPE (detergent bottles, etc.) from undyed HDPE (most milk jugs). 

Workers also remove the two kinds of contamination. First, the mechanical sorting occasionally sends materials in the wrong direction. Plastic may get mixed with cans, for example. Second, some trash makes it past presort.

My tours of the MRF in High Point, North Carolina demonstrate the capabilities of human workers more dramatically than Greensboro. When I called for an appointment, I learned that High Point was in the process of installing a completely new system. Naturally, I wanted to see both.

Half of the older system had been taken down to make room for the new machinery. It had no machine sorting at all except a magnet at the very end to remove the steel cans. Formerly, its machinery had separated two-dimensional and three-dimensional items. At the time of my visit, everything had to go through the remaining system twice.

Each worker pulled off certain recyclables and threw them into the proper bins. They’d separate different kinds of paper on one run-through and different three-dimensional objects on the other. 

At the end, whatever remained on the conveyor belt after the second run-through fell into a trash bin and from there to the landfill. 

The new system has much more sophisticated automation than Greensboro’s. Workers on at least some of the lines perform a negative sort. So instead of picking off mixed paper, for example, I watched the same people leaving the paper and removing only contaminants from the belt. In other words, they had spent years on the old system picking up recyclable mixed paper. Now they have to watch the paper go past while they pick up everything else. 

This work is monotonous and potentially dangerous to the workers. Robotic sorting with artificial intelligence is on the horizon. For now, however, it’s prohibitively expensive. 

Baling and shipping

At the end of sorting, everything has been separated into the various commodities, which the MRF will then sell. It goes from these large bins to a baler, which compacts it and ties it with baling wire. The MRF stacks bales of similar materials together until a buyer sends a truck to purchase them.

Too many American MRFs relied on selling their output to brokers who, likely as not, shipped everything to China. Then, in 2019, China stopped accepting most of the world’s recycling. The Chinese crackdown sent the entire recycling industry into turmoil. Years before that, it had so eagerly collected recyclables that they priced American companies out of the market. 

Nevertheless, there have always been American markets for the materials that recycling facilities collect and sort. These buyers process it further. For example, some of them clean plastic and shred it to make raw materials for manufacturing new bottles, polyester, and other products. 

Much of the public would like to buy recycled products. As more American companies arise to make them or process materials for them, the value of all those bales of recyclables will increase. The current crisis in recycling will pass.  

About the pictures: 

Unless otherwise noted, I took the pictures. Greensboro contracts with a commercial company, which did not allow me to take pictures. The city of High Point operates its own MRF. I did not take pictures of the old system. I also visited the MRF in  Bowling Green, Ohio, which is operated by a non-profit corporation. 

Sources:

10 points that explain mixed waste processing / Allan Gerlat, Waste 360. July 6, 2015
Anatomy of a recycling facility / David Guion, Cleantech Solutions. May 31, 2017
The large, the small, the clean and the dirty: equipping MRFs / Erik E. Colville and Nancy J. McFeron, Waste 360, November 4, 1994
Montgomery considers new monthly recycling fee added to your bill / Brad Harper, Montgomery Advertiser.  August 21, 2020
Montgomery recycling partnership works to expand commodity sales / Jennifer Horton, WFSA12 News. February 4, 2020
The recycling process: what happens behind the scenes? / David Guion, Sustaining Our World. April 20, 2017

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