How single-stream recycling works—your choices can make it better

Image credit: PHYS.ORG

We’ve written before about wish-cycling, the tendency to hope that what you put in the recycling bin is actually recycled. An April 17, 2025, article in PHYS.ORG reviews the current status of recycling in the U.S. Single-stream recycling is the term given to the process where we put all of our recyclable material in a single bin, understanding that it will be recycled. A 2019 report by The Recycling Partnership found that 15 – 25% of materials in single-stream processes end up in the landfill.

Less than 9% of all plastic is recycled in the U.S. But why?

According to PHYS.ORG, “Contamination, such as food residue, plastic bags and items that can't be recycled, can degrade the quality of the remaining material, making it more difficult to reuse. That lowers its value. Having to remove that contamination raises processing costs and can force recovery centers to reject entire batches.”

Some plastics typically can not be or are difficult to recycle.

• Symbol 3—Polyvinyl chloride (PVC) degrades easily, and melting can release toxic fumes during recycling, contaminating other materials and making it unsafe to process in standard recycling facilities.
• Symbol 4—Low-density polyethylene (LDPE) is prone to getting tangled in sorting machinery at recycling plants.
• Symbol 6—Polystyrene, often used in foam cups, takeout containers and packing peanuts, is lightweight and brittle, difficult to collect and process, and easily contaminates recycling streams.

These three plastics can be recycled in many facilities.

• Symbol 1—Polyethylene terephthalate, or PET, widely used in soda bottles.
• Symbol 2—High-density polyethylene, or HDPE, commonly used in milk jugs and laundry detergent bottles.
• Symbol 5—Polypropylene, or PP, used in products such as pill bottles, yogurt cups and plastic utensils.

However, even these materials have challenges.

When ground up PET, HDPE, and polypropylene are placed in water, the PET sinks and can be separated from the other two. The HDPE and polypropylene both float and can't be recycled together. So, more advanced and expensive technology is often required to separate those two materials, making them unattractive for recycling by some facilities. If they are mixed and attempted to be recycled into new plastic, they are often brittle and unusable for new products.

PHYS.ORG says “You can help the recycling process by taking a few minutes to wash off food waste, avoiding putting plastic bags in your recycling bin and, importantly, paying attention to what can and cannot be recycled in your area.”