Recycling · Jun 5, 2022 Back to Blog

Where Do Your Recyclables Go?

A Virtual Tour of a Materials Recovery Facility

Ever wonder what happens to your recyclables? Understanding how material is recycled illuminates what works well in the recycling system and where improvements, investments, and policy changes are needed to guide us toward a circular economy and a Zero Waste society.

Your recycled material will be touched by many people, machines, and technologies, and may travel many miles before it ends up back in a new product. After the recycling cart, the next stop for your recyclables is a materials recovery facility (or MRF) where the materials are sorted out into different categories such as paper, aluminum, and types of plastics. The goal of a MRF is to sort out valuable, usable material and prepare it for the market. 

MRFs do not manage waste. They produce feedstock for manufacturing new products.

There are more than 350 MRFs in America and while no two are exactly alike, most MRFs process the same core recyclable materials using similar combinations of equipment, labor, and technologies. There are also some key differences. MRFs come in all sizes and vary widely in their level of technologies; there are also regional differences in what is recyclable based on local manufacturing facilities. This is part of the reason why recycling is not the same across the country.

Put on your hard hats, pop in your ear plugs, and put your safety glasses on. Let’s go for a MRF tour.

Overview of a MRF

1) Tipping Floor

First, all of the material collected from by curbside recycling programs collection trucks

To begin the process at a MRF, all of the material collected from curbside recycling programs is dumped out on a giant pile on the tipping floor. From the tipping floor, the material is loaded onto a conveyor belt by machinery.  

What is in the pile of recyclables? It’s mostly paper, cardboard, glass bottles, aluminum and steel containers, and plastic containers. This chart shows an average mix of recyclables from US households.   

2) Pre-Sort

The recyclable material then goes through a pre-sort, where recycling workers separate out non-recyclable material. MRFs receive all sorts of stuff placed in curbside carts by mistake that is not recyclable, like furniture, food, bowling balls, holiday lights, umbrellas, batteries, propane tanks, scrap metal, carpets, yard waste, and many, many other objects. We call these non-recyclable, potentially dangerous materials inbound contamination. These objects may injure workers, cause damage to machinery, increase sorting costs for the recycling program, and decrease the value of recyclables. 

It’s hugely important that residents and businesses follow guidelines carefully to avoid putting these materials in the recycling cart in the first place. Strong education programs are key to reducing inbound contamination; best-in-class MRFs have inbound contamination under 10%, while some poorly run programs may have up to 25-30% inbound contamination. 

Other objects may get stuck in our machinery. We call these objects tanglers (like plastic bags and Christmas lights). 

We pull out plastic bags during this step, which get caught in the MRF machinery, causing costly delays and equipment damage. Plastic bags are one of the most costly contaminants in the MRF. 

3) Materials Sorting

Next, materials are sorted based on material type, size, and weight. 

Cardboard & Mixed Paper 

A typical MRF will first remove the fibrous (i.e., paper) material like cardboard and paper from the stream. Larger pieces of cardboard are typically pulled off first using large star screens where the cardboard floats over the top. MRFs use a series of sifters and star screens to separate out the 2-dimensional materials (like paper and cardboard) and the 3-dimensional materials (everything else). The flat, 2-D paper materials float over the screen while the 3-D containers fall down through the screen. 

Machines like tumblers and paper optical sorters pull the remaining paper products from the rest of the stream. Most MRFs produce a mixed paper grade that includes a mix of newspaper, white paper, some paperboard, and other paper products. Other MRFs might sort into more specific paper categories. 

Likely End Markets: Mixed paper is used to make new cardboard, cereal or cracker boxes, newspaper, and other paper products.

Metals 

Magnets pull steel and tin out of the stream. Eddy currents are used to separate out aluminum cans by creating a brief magnetic current to repel the aluminum, which causes it to fly up over a divider while all other materials fall down. 

Likely End Markets: Metals are recycled back into cans or used in automotive parts, building materials, and appliances. 

Glass 

Glass is highly recyclable but it can be challenging to sort because it breaks into small pieces in the trucks and at the MRF. Many MRFs use this to their advantage and crush glass with a glass crusher, which has steel discs that shatter the glass. The material is then run across a fine screen and anything smaller than 2 inches will fall through (like the broken glass) while the rest of the material continues down the sort line. Even though glass can be recycled indefinitely, not all MRFs accept glass. MRFs need a regional buyer to send the glass; because glass is heavy, it cannot be transported long distances for recycling. Learn more about efforts to expand glass recycling.

Likely End Markets: Recycled glass is used to make new glass bottles or jars or fiberglass insulation.

Key contamination issue: this is where small plastics end up contaminating the glass stream as bottle caps and other bits fall through. Some MRFs may run additional processing to remove these contaminants but it is not standard. 

Plastic Bottles, Tubs, Jugs & Jars

MRFs only accept a very small fraction of all plastics for recycling. Most MRFs accept plastic bottles, tubs, jugs and jars. These plastic containers must be separated from the other non-plastic materials and then further separated into different types of plastics. It is becoming more common for MRFs to use optical sorters to sort plastic based on their resin type (denoted by the number printed on the container). Optical sorters use sensors and artificial intelligence, aka a software-driven image processing system, to sort material based on color, shape, and chemical composition. 

In this example, the optical sorter is programmed to look for PET plastic. When the sensor sees a PET bottle, a puff of air is released and moves the bottle over the divider while the rest of the material falls down. Though the optical sorters are relatively effective, in-person quality control is still needed to sort out contaminants. 

In many MRFs, some plastics are still sorted by hand, which is very labor-intensive and costly. Each sorter is typically assigned a grade of plastic. For example, one person grabs colored HDPE bottles while another person grabs clear HDPE bottles, and another sorter grabs yogurt containers.

A new technology many MRFs, including AMBR members, are testing out are robots, an automated machine used to sort plastics. The robots have potential to reduce labor costs and may help improve data collection within the MRF. Optical sorters are expensive equipment so each MRF must consider capital costs, labor costs, market values, etc. in determining if or when to install optical sorting or other equipment.

Likely end markets: The end market for plastics is dependent on the plastic type—indicated by the number stamped onto most plastics. For PET containers, markets include new bottles, carpet, and polyester fabrics. Most HDPE is used for new bottles or drainage pipes.

Plastics are the most challenging materials to recycle in a MRF and cause a lot of confusion among residents and businesses.

4) Materials are Baled and Shipped to End Markets

After the material is sorted, it is baled into compressed rectangular blocks and wrapped with wire to contain the bale. The bales are sold to either secondary processing facilities or to manufacturers to be turned into new products or downcycled into other products. 

Most MRFs produce the following bales of materials: 

  • Cardboard
  • Mixed paper
  • Aluminum cans
  • PET bottles (#1) 
  • HDPE bottles-natural (#2)
  • HDPE bottles- colored (#2)
  • Steel cans

Some MRFs are able to recycle: 

  • Glass
  • Polypropylene tubs & lids (#5)
  • Mixed rigid plastics (#1-7)
  • Aseptic cartons (milk cartons and juice boxes)

5) Understanding MRF Economics

The MRF sells the sorted recyclables to manufacturers and secondary processors. MRF operators’ decisions around what they can economically accept and process are based on their revenues and costs, just like any other business. The revenue from the sale of materials needs to cover the costs of sorting and processing those materials. The value of the recyclable materials fluctuates like other commodities and depends on many factors, including the price of oil, material shortages, and other economic factors. When market prices are high, a MRF may accept materials from haulers and municipalities at no charge or even pay for the materials. Conversely, when markets are low, a MRF may need to charge to accept recyclable materials.

What makes something recyclable?

There are many factors that go into what makes something recyclable. In general, materials need to meet the following criteria: 

  • End Market: There must be an end market or a company that wants to buy the recycled material. Ideally, there are multiple, dependable buyers who are transparent about what products the material will be made into. 
  • Economics: There must be value in collecting, sorting, and shipping the material–the sale of the material must be greater than the processing costs. 
  • Sorting: The material must be sortable: a materials recovery facility must be able to sort the material with either equipment or labor.
  • Scale: Recyclers also must be able to collect enough of the material which is impacted by recycling infrastructure and consumer behavior.