5 August 2010 - 20:36Compostable cup update

The cups have been buried for two months now. I dug them up and took a look:

Cups after two months in the ground

Cups after two months in the ground

The compostable cup is on the left, with the control cup on the right. They don’t look too much different to me. There are more cracks in the compostable cup, but that might just be due to different mechanical properties or having been abused differently in the burial.

I have reinterred both cups. We’ll see what happens. Having read some more about compostable plastic, I am not optimistic. It can decompose in a warm compost heap into nothing but carbon dioxide and water, but when buried without air it can anaerobically become methane, which is a worse greenhouse gas. If cups are going to be put into landfills, it’s probably better if they’re normal plastic and don’t decay. This will at least sequester the carbon. Still, for the sake of my experiment, I will leave this one in the ground. What’s a little methane between scientists?

2 Comments | Tags: Uncategorized


  1. I may have been mistaken, but I thought that the whole point of compostable plastic was that they go into composting systems, not into landfills. In SF we have municipal composting that takes things like used paper napkins, waxed paper milk containers, and compostable “plastics.” Living in the Norcal bubble, I sometimes forget that not everyone has access to such programs.

    So you’re looking at it as “If cups are going into landfills they should be standard plastic” and I’m looking at it as “If I must use a disposable cup, better for it to be something that can go in the composting stream rather than the landfill stream.”

    I guess the real question is, how do we wean ourselves off the addiction to disposable containers of ANY sort?

  2. Maybe the point is for them to go into a compost stream rather than landfill, but I seriously doubt that ones sold here will. More likely they go straight to the incinerator, which isn’t any worse than having a regular plastic cup go there. But if the compostable cup goes into the landfill and becomes methane, that’s twenty times as bad as if a conventional cup get incinerated.

    I’ve been thinking for a while, but have been too lazy, to put together a post on the idea that the best (reasonably possible) use for oil is for it to be turned into plastic in landfills. Any oil for which this happens is sequestered more-or-less permanently. If you assume that essentially all oil that can be extracted from the ground will be, it’s better for it to be cups put back in the ground than burned and end up as atmospheric CO2.