Understanding Recycling Contaminants in Manufacturing Recycled Building Materials

August 14, 2010

From the Single-Stream Recycling Guide comes a refresher list all recyclers should know about: the dirty dozen of contaminants that turn the idea of user-friendly and earth-friendly single-stream recycling topsy-turvy for manufacturers of recycled building products.

Topping this list, of course, are plastic bags. Other than a convenient way to pick up dog turds, the plastic bags so prevalent in stores are a recycling company’s Waterloo. “Plastic bags are the worst contaminant in the recycling bin,” contends Eco-Cycle, author of the Dirty Dozen list.

The list also includes materials that have been tossed into unwanted plastic bags. Conveyor belts in recycling plants continually need to be slowed to sort out the messes, adding an unreasonable operating expense. Other items include plastic lids and caps – neither of which are recyclable. The problem worsens when somebody leaves the lid on the bottle.

Contrary to what many purists think, the same holds true for shredded paper, for it is too small to sort. Finalizing the Dirty Dozen are non-recyclable plastics, containers with caps or lids on them, bottles containing liquids, ceramics, diapers and bio-hazardous waste, hazardous waste, scrap metal and frozen food containers.

There also are other contaminants that muck up the recycling process. Used pizza boxes top off this list, writes the Stanford Recycling Center, expanding on this simplified list of contaminants by providing a useful set of questions and answers concerning other items such as pizza boxes, paper that has been smeared with food, used paper towels, and photographs.

Lori Brown, writing for Earth911.com, elaborates on how used pizza boxes in the above photo can pollute single-stream recycling: “Food is one of the worst contaminants in the paper recycling process. Grease and oil are not as big of a problem for plastic, metal and glass, as those materials are recycled using a heat process. But when paper products, like cardboard, are recycled, they are mixed with water and turned into a slurry. Since we all know water and oil don’t mix, the issue is clear.

“Grease from pizza boxes causes oil to form at the top of the slurry, and paper fibers cannot separate from oils during the pulping process. Essentially, this contaminant causes the entire batch to be ruined. This is the reason that other food related items are non-recyclable (used paper plates, used napkins, used paper towels, etc).”

Best advice for all: when recycling something, know what will contaminate the recycling process, and what will make for better recycled building products.


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Glenn Meyers

Writer, documentary producer, and director. Meyers is a contributor to CleanTechnica, and founder of Green Streets MediaTrain, a communications connection and eLearning hub. As an independent producer, he's been involved in the development, production and distribution of television and distance learning programs for both the education industry and corporate sector. He also is an avid gardener and loves sustainable innovation.