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I was told some months ago that paper and cardboard recycling processes need clean raw material. In particular, paper stained with oil may be inappropriate to recycle, and should rather be thrown away.

Where I live we separate our waste between:

  1. glass
  2. paper, cardboard, recyclable plastic containers, metal cans
  3. garbage, that is, everything else

When I happen to have a used pizza box, it is often stained with oil.

As I am not aware of the chemistry that is at stake for paper/cardboard recycling, I don't know if I should throw the oily pizza cardboard in the recycling or the trash. More finely, how oily can the cardboard be and still be a good candidate for recycling?

  • 4
    I find the lid of the box is often clean, so I rip that off and recycle it at least... it's a good question though; how much contamination is ok? – Highly Irregular Apr 8 '13 at 21:52
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    Unfortunately, as much as we want to maximize our recycling, if a batch of recycled paper is contaminated then the whole batch will have to be discarded. So in this case it is better to be conservative when in doubt. – half-integer fan Apr 10 '13 at 23:09
34

According to Stanford University, soiled food packaging should not be recycled like unstained paper and cardboard waste:

Q: Why can't pizza boxes be recycled?
A: Pizza boxes are made from corrugated cardboard, however the cardboard becomes soiled with grease, cheese, and other foods once the pizza has been placed in the box. Once soiled, the paper cannot be recycled because the paper fibers will not be able to be separated from the oils during the pulping process. Food is a major source of contamination in the various paper categories.

  • 6
    It's a shame they don't provide a definition for what counts as soiled. Small amounts of contamination might be ok. – Highly Irregular Apr 11 '13 at 7:54
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    In Boise, Idaho, US they used to prohibit food-contaminated cardboard (and still sort of do), but recently, on the official Facebook page of single-stream recycling program they stated that pizza boxes can be recycled, so long the food residue is scraped off (greasy spots are supposedly fine). So, who knows. Maybe technology improved? – theUg Apr 30 '13 at 6:02
  • I elected to throwing the bottom to trash and the top to paper container. – Tomáš Zato Nov 15 at 14:02
30

it is worth noting that although you can't recycle pizza boxes as cardboard, this doesn't mean you have to merely throw them away either. They form an almost perfect barrier layer for sheet mulches for example and you can compost them otherwise keeping in mind that they are a "brown" (i.e. high carbon, low nitrogen) and therefore act as a bit of a nitrogen sink in the compost pile.

There are a number of strategies for doing this. The most simple (as I mentioned above) is sheet mulching where soil may be disturbed but then covered with something like pizza boxes, newspaper, and other high carbon barriers, then packed with various layers and then left to compost in place briefly before plants are planted in the composting material.

So just because you can't recycle it into more cardboard doesn't mean it is best thrown away.

  • 1
    Local reuse is almost always better than transport for recycling. The exception being things like reusing high embodied energy materials (like aluminium or titanium) as filler where it's replacing low embodied energy material (usually rock or timber). – Móż Jul 24 '13 at 0:11
7

Our local recycling center now takes food-soiled paper products for use in their composting program. You might look into that and see if there is anything like this in operation where you live.

5

There were two great related articles in The New York Times last month concerning recycling:

In the latter article they specifically address the subject of pizza boxes as one of the six:

Pizza boxes are among the most common offenders when it comes to contamination, waste managers say. The problem is that oil often seeps into the cardboard. The oil cannot be separated from the fiber, making that material less valuable, and less marketable, to buyers.

But that’s not to say you can never recycle a pizza box, said Marjorie Griek, executive director of the National Recycling Coalition, which promotes recycling in the United States. “If you’ve got a few crumbs in there, that’s not an issue,” she said.

Pizza boxes with “small amounts of grease” are O.K. to recycle in New York City, a sanitation department spokeswoman said. If the grease seeps through the cardboard, the box should be put in a composting bin or thrown out, she said.

Remember, there are also two sides to a pizza box. If there’s a side that’s not oily, tear that off and recycle it.

The other thing I loved about this article is that it introduced to me the phrase/concept of "aspirational recycling"... that is the act of recycling items that you hope will be recyclable. In many cases items flowing into the recycling stream that not truly recyclable may result in the entire batch being discarded (this topic is covered in depth in the former article).

The conclusion being that you really need to know if greasy pizza boxes are recyclable in your area. If you are just acting on your hope they are you may be doing much more harm than good.

2

Self answer, a bit off-topic maybe (depending on whether compost is considered recycling):

If like I do, one considers composting a cleaner/higher/more efficient way of recycling, then for months (almost two years I think) I have been putting the pizza cardboards in my vermicompost/lombricompost device.

Oil is not an issue for the worms, they eat it all the same.

That requires no chemical treatment to recycle the cardboard totally. I grow plants with the earth obtained after such recycling.

The worms are obviously fond of cardboard, and I have been told it helps for the pH equilibrium of the compost.

(I do not only put cardboard in my compost, I also put paper not reusable. One has to make sure there is not too much plastic on the paper though)

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    Good answer, but be careful with fat or salty food leftovers, those can be harmful for the worms. Also you say "...not too much plastic...", I'd recommened no plastic at all because that will degrade into microplastics and contaminate your compost. – THelper Aug 30 at 13:44
  • @THelper, I have started going into zero waste for those almost two years, and one of the consequences is that I tend to have no leftovers at all ;-) To the compost what is left is only vegetable peelings. But it may have happened from time to time I put in the compost a forgotten plate that has been too long in the fridge: so I'll be careful that it should not be too salty. Thanks for the remark. – Stephane Rolland Aug 30 at 14:39

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