If your city allows you to throw all of your recyclable materials in the same bin, then your city uses a process called “single-stream recycling." Single-stream recycling means there is no need to separate different materials such as paper, plastic, and glass into separate bins.
Instead, all recyclables can be tossed into the same bin. They are then collected by a truck and hauled to a sorting center where the real magic begins.
The separation process starts when the truck arrives at the Materials Recovery Facility (MRF). The process may vary from place to place, but each MRF has one goal: to separate and recycle different materials so they can be made into new products.
Let's take a tour of the Wonderopolis MRF:
Step 1: The recycling truck unloads materials. Materials are carried along a conveyor belt to a v-screen separator. The v-screen separator divides out newspaper, cardboard, and other paper items.
Heavier materials like plastic, metal, and glass fall through the separator to a conveyor belt below. The collected paper products are bundled to get ready for processing. Plastic, metal, and glass items continue their journey onward.
Step 2: Next, metals are recovered from the recyclables using a two-step process. First, giant magnets attract ferrous metals. These items include iron, tin, and steel.
The magnets remove ferrous metal products from the belt and place them in a bin where they can be prepared for a metal mill. Can you name some items made of iron, tin, or steel that may end up on the magnet during this phase of the metal recovery process (e.g., tin cans, tools, automobile parts, etc.)?
Step 3: Since aluminum products, such as soda cans, are not magnetic, they continue along with the plastic and glass recyclables toward an eddy current rotor. Eddy currents create strong fields of energy around nonmagnetic materials.
Now it's time for physics to step in to lend a hand. The eddy current causes the aluminum items to shoot away from the other items on the belt and into a collection bin.
Step 4: By now paper, ferrous metals, and nonmagnetic metals have been sorted from the bunch. That leaves plastic and glass to continue along the belt. During the next step, an optical scanning system recognizes plastic materials and pushes them off the belt into a bin using a blast of air.
Step 5: Having said goodbye to all the other types of recyclables, only glass remains on the belt. The heavier glass items reach the end of the belt and are collected in a bin. This step completes the recycling process.
Now that you know how the collection process works, let's tag along with paper, metal, plastic, and glass to find out what happens beyond the conveyor belt.
When paper arrives at the mill, it is loaded into a “de-inker." This machine removes ink from paper fibers through a chemical washing process. After de-inking, the paper is mixed with water and solvents in a giant blender called a “pulper." The resulting product is called pulp slurry.
The pulp slurry is then moved to a giant washing machine that spins it at high speed, removing any unwanted particles such as string or glue. After washing, the clean pulp continues on to a press and is wound onto giant rolls.
Unlike some other recyclables, paper degrades each time it is recycled, so it can't always be used to make new paper. It can be used to make insulation for homes and even toilet paper, though! Can you think of other recycled paper items you have used? Some examples may be picture frames, paper towels, and books.
After leaving the MRF, metals are sent to a metal mill. Using extremely high heat (up to 2800° F or about 1538° C!), the recycled metals become a molten liquid. The molten metal is cast into molds, becoming metal bars called "ingots." The ingots are then shipped to manufacturers who use them to make everything from aluminum cans to file cabinets, tin foil, and even bridges!
If you look on the bottom of most recyclable plastic items, you will see a number. Each type of plastic is given a number from one to seven. When recyclable plastic arrives at a reclaiming facility, it needs to be divided according to its number. The most common type of plastic is #1. This is the plastic used to make soda and water bottles.
Once sorted, the plastic moves along a belt and is fed through a grinder. Here it is chopped into little bits, kind of like plastic flakes. The flakes are fed into a furnace and melted down into a polymer. The polymer can then be used to make new products such as lawn furniture, garbage cans, and carpets!
Recycled glass may arrive at the reclaiming facility in all sorts of sizes and shapes, but that doesn't last for long. The first step is to crush all the glass into tiny pieces called "cullet."
Cullet can either be sent directly to manufacturers or placed in a furnace where it is heated into molten glass for repurposing into new products. Some products made from recycled glass include glass doorknobs, floor tiles, garden ornaments, and even jewelry beads.