UW News

December 19, 2012

Composting confusion rampant in UW waste bins, study finds

News and Information

A study of waste bins at the University of Washington’s Seattle campus revealed that 88 percent of the contents in trash bins could have been recycled or composted. Most – 72 percent – of what didn’t belong in trash bins turned out to be compostable items, such as food, carry-out containers and paper coffee cups.

students sort trash

Students in Jack Johnson’s archaeology class at UW sort trash, compostables and recyclables.Alex Credgington, UW

“Food waste is the single most significant contaminant in trash bins,” said Jack Johnson, a UW archaeology graduate student who leads the UW Garbology Project. “It is clear that most contamination stems from people throwing the contents of their on-campus meals, including foods and compostable/recyclable packaging, into trash bins,” he wrote in a report (pdf) posted this week summarizing the project’s findings.

Finding ways to improve composting would cut the university’s waste expenses. It costs $145 per ton to dispose of trash compared with $55 per ton for compost, which ends up turned into nutrient-rich soil by Cedar Grove. There is no fee for recycling.

Johnson and his students in an archaeology class spent five afternoons this fall sorting and weighing campus waste collected from two of the seven BigBelly Solar kiosks on Red Square. The kiosks include bins for trash, recyclables and compost. Clad in white, water-resistant jumpsuits, blue specialized gloves and breathing masks, the group wanted to see how effectively campus users were categorizing their waste.

Based on trash from the two kiosks in Johnson’s study, 67 percent of waste was diverted from landfills by people putting it in compost or recycling. Looking at campus recycling programs as a whole, UW Recycling finds that the diversion rate is 57 percent, though they are working to increase that to 70 percent by 2020.

“It’s definitely achievable,” Emily Newcomer, UW Recycling manager, said of the goal. “UW is a city within a city, with people from all over the world. The challenge is helping everyone understand recycling and composting, and educating them on what goes where.”

The diversion rate in Johnson’s study fell to 54 percent when his group factored in whether campus users were correctly sorting their waste.

Trash bins showed the most miscategorizing, usually with items that should have been composted. Recycling bins revealed confusion too, where a quarter of the mass accumulated was compostable food waste – mostly liquids that should have been poured into the compost bin and then the bottle recycled. Contamination was only 7 percent in compost bins, suggesting that those who use the compost bins are accurate in identifying compostable materials.

Johnson and his research team estimate that only about 5 percent of what is thrown out on campus is actually trash – everything else could be recycled or composted. They suggest these ways to improve:

  • Pouring out liquids. Most contamination in recycling bins was from food, usually liquids. Johnson estimates that at least 60 percent of recycling contamination would be eliminated if people simply poured out liquids before recycling.
  • More education on what is compostable. Most carry-out containers of food purchased on campus are compostable, yet many campus users treat them as trash. Better labeling of containers might help with this, Johnson’s group points out.
  • Increasing the number of campus compost bins. The researchers found that the kiosks accumulate 14 times more compost than trash, yet they point out that campus-wide there are more trash bins than compost bins.
  • Increased promotion of incentives for reusable cups. Several hundred cups for coffee, soda and soup – about 7 percent of the waste examined by the team – were recyclable or compostable. The amount seems like “wanton wastefulness,” Johnson wrote, and it might be reduced if more people participated in programs like UW’s Housing & Food Services’ discounts for bringing their own cups.


For more information, contact Johnson at anamgorm@uw.edu, or Newcomer at 206-685-8928 or emilyn2@uw.edu.