Why I hate recycling conversion factors

In measuring recycling performance you must have some sort of data. Right now everyone wants that data in tons.

Tonnage is fine when you’re dealing with a weighed container (a compactor or scale truck), but otherwise you’re stuck converting volume to weight.

I’m constantly asked, “What’s the conversion factor for (name your material stream)?” People generally don’t like my answer, “Well, it depends.”

Yes. There are industry standards available. The EPA, RecycleMania, and King County (the county Seattle is in) all have compilations of standard conversions. (I personally like the King County one because I’ve found it to be the most comprehensive, not just because I used to live there).

However, none of these standard conversions really address the waste streams I deal with.

I need to determine the weight of a cubic yard of pantry trash from a commercial office building, which is mainly made up of empty food packaging from employee breakfast, lunch and coffee breaks. A cubic yard of pantry trash is going to be different from a yard of back-of-house cafeteria trash, which is made up of a lot of prep food waste (heavy stuff), plastic wrap and plastic gloves.

I need to determine how much a cubic yard of mixed paper weighs. Not just white ledger, or just newspaper, or just magazines. We’re talking a real mix of paper that includes paper bags, crumpled paper, paper board boxes, post-it notes and file folders in addition to the non-crumpled white ledger, newspaper and magazines.

I need to determine the weight of a cubic yard of co-mingled glass, metal and plastic. The plastics and aluminum aren’t too bad, but throw in a couple of glass bottles and your conversion could be way off depending on how much of what material you’re calculating for.

Then there’s cardboard. Some boxes are large, some are small, some are flat and some are whole – and that’s just loose. Baled cardboard is a whole other story.

Any one who deals with trash knows it isn’t an exact science. There’s going to be some estimation involved, and sometimes that estimation involves a little more work (like weighing bags, or going through a few bags.)

I’m not saying don’t use standard conversions at all. They can be very helpful. But make sure to take into consideration the composition of your material streams. That way you’ll be able to determine more accurate conversion factors, which will in turn give you more accurate waste data.


About Amy Marpman

Director of Recycling Services at Great Forest, Inc. in NYC. Continually finding the balance of idealism with the practical realities that make or break recycling programs.
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