By Roberta Miller

For many years, I have had to opportunity to work with school districts on a variety of waste reduction and recycling projects. Together, we have calculated the cost of purchasing recycled-content paper, figured out cost saving by using a chipper to process tree trimmings and how to set up classroom and cafeteria recycling/food scrap collection programs. School districts are creative and innovative institutions but can also implement projects that create unintended consequences.

Recently I have heard that some school districts have begun purchasing and installing expanded polystyrene (#7) lunch tray densifiers. According to the manufacturers of the densifiers, these machines process food-soiled lunch trays from the school cafeterias by applying heat and create a condensed brick that can be used as manufacturing feedstock for picture frames, flowerpots or other plastic products.

The first unintended consequence of these densifiers could be increased labor costs. The densifiers require polystyrene trays be fed into the machines, a task that would most likely be done by custodial staff. Another consequence could be higher energy costs. These costs would obviously depend on a whole host of factors like time of day the machines are used, local energy costs and the number of trays processed. Also possible are questionable air emissions created by the densification process. The densifiers produce bricks for which it is challenging to find an end use. The bricks are not something that can be handled by the district’s existing recycling service provider. The densifiers are also not inexpensive — one district was quoted $10,000 per densifier.

While the expanded polystyrene trays are less expensive per unit to purchase, fewer and fewer school districts are using them due to high disposal costs. Fortunately, in areas with readily available and cost effective commercial organics collection, many school districts are choosing to use paper food service trays. After lunch, the paper trays and any remaining food can be stacked, saving both space and time in the fleeting minutes of a school lunch period. This saves time for the custodian working the lunch room and most likely has the next group of students ready to grab their lunch before hitting the playground. The ability to quickly pull the bag of stacked paper trays and put them into the organics dumpster can make a custodian’s job easier.

There are many factors to consider before purchasing a densifier and I would encourage any district to carefully examine their entire food service process and waste management system prior to purchase and installation. Expanded polystyrene food trays are petroleum products that aren’t readily recyclable in existing recycling programs. I remain skeptical that densifiers are a sustainable alternative to readily compostable paper trays in the vast majority of applications.

When evaluating any new sustainability initiative, it is always important to consider the entire life-cycle of a product or process to assess its impact. Innovative projects with good intentions can sometimes have unintended consequences.


Roberta Miller is the Greening Committee Chair at the California Resource Recovery Association; Program Manager at the Alameda County Waste Management Authority & Recycling Board, StopWaste.Org; and a School Circle Sustainability Coach at True Market Solutions.