Oct 22, 2008

Biodegradable plastic bags DON'T

About a year ago I acquired a few of the fancy new corn-based biodegradable plastic bags at a couple of City events. When I was done with them I dropped them in my Green Cone food composter.

You use Green Cones by dropping all your kitchen vegetable waste into them, then let them lie undisturbed for about a year (it's best to have 2 of them) and open them up and take out the lovely moist soil that the food waste has transmogrified into, and put it on your garden!

I opened my Green Cone last week to find that all the vegetables had indeed rotted down to dirt but that (even after a year) the plastic bags were (Drum Roll, yes you guessed it) unchanged and good as new.

I fished the bags out, cleaned them off and photographed them to prove it to you!

Pictures (from the top):

My sample was small: two of one type of bag, and two of another. However, as you can see from the pictures: none of them showed any sign of decomposing, even after a year in intimate contact with rotting vegetables and worms.

The City of Seattle has outlawed styrofoam ware, so venders will be using (and you will be paying for) these supposedly "biodegradable" items.

My question: Are they really any more biodegradable than my seemingly immortal "biodegradable" bags?


j said...

oh, man, this kind of stuff just feeds my cynicism. Then I feel justified when I get lazy about recycling, etc. I hope Trellis can explain.

In the meantime, all the more reason to limit all consumption -- "green" or not.

Ross said...

"Are they really any more biodegradable than my seemingly immortal "biodegradable" bags?"

In my experience the answer is yes.

I used to use the ones they sell at Madison Market (sorry can't remember the brand name... they are light green colored.) I actually stopped using them because they biodegrade *too fast!* If I had moist stuff in the trash can for more than about 3 days, when I lifted the trash bag it would stretch out and sometimes break. When my roll ran out I just started taking from the mass of random plastic bags I have stuffed in a bottom drawer in my kitchen.

Anonymous said...

Trellis has changed their formula 3 times in the last year to find the right balance between biodegrading too fast and not fast enough. In the end they determined to optimize the formula for the anaerobic conditions of a landfill because that is where 95+% of all waste ends up, biodegradable or not. Anaerobic bacteria are also used in biodigestors which are the next wave in recycling. Their formula strikes a balance between "zero waste" and strength of material and cost -- their products do not cost more than regular materials. It's good progress but not all things to all people -- and not for those using backyard composting which they do not claim on their website or in any of their materials.

dave said...

I'm not planning on putting these in my compost, but I'm assuming that they will decompose in the landfill at some point.

Andrew Taylor said...

I contacted the company: no overt reply but the anonymous post is probably from them.

Bags designed only to decompose in a landfill raise an interesting issue: WHY BOTHER? We get no useful compost from them, just carbon emissions.

No-decomposing plastic bags might be better: they come from the ground as hydrocarbons (oil) and return to the landfill as (non-decomposing) plastic (ie still hydrocarbons). They take up little room and can't use much oil - they're so lightweight.

Andrew Taylor said...

Thanks for sending this link Andrew - good blog posting. As far as I can tell, compostable/biodegradable bags only break down well in industrial composting operations, such as Cedar Grove Composting, where our collected yard waste and food waste goes....

King County Solid Waste Division
- EcoConsumer columnist for the Seattle Times