Breaking It Down: The Corn Plastic Bottle That Wouldn’t

A larger piece of the "green" bottle at week five in the compost pile.

A larger piece of the "green" bottle at week five in the compost pile.

This post was written by John Mulrow, Worldwatch Institute MAP Sustainable Energy Research Fellow.

The Green Bottle has reached week 5 in my backyard compost pile. I admit that the past few weeks have not been ideal for backyard composting: the recent rain cooled the pile, reducing the speed of decomposition, and it’s been giving off a funky, mildly rotten odor when it should smell refreshing and forest-y. This likely means that either an abundance of moisture or a lack of oxygen is currently inhibiting aerobic digestion of the organic material.

Despite this small setback, as you’ll notice in the weekly photos, the carrots and tomatoes that went in the same time as the bottle are nowhere to be found. And nearly all the food, except for a couple corn husks and egg shells, has been reduced to finished compost.

But the corn plastic remains as intact as it did after just one week in the pile.

Since our last post we’ve dug deeper into the facts about the corn plastic used to make the bottle.  Naturally Iowa uses a biopolymer (a plastic made from organic rather than petroleum-based materials) called Ingeo. According to the manufacturer’s website, “Ingeo is intended for industrial-based composting systems which regulate temperature, moisture, and aeration.” The company also explicitly discourages including Ingeo in home composting systems, “due to inconsistent control of moisture and oxygen.” While the plastic may not be meant for my backyard compost pile, it will have to stay there for now because the nearest industrial compost site is over 30 miles from where we live in Washington, D.C.

But industrial composting is growing in the U.S., with efforts like residential food-scrap collection starting in multiple cities. As a result, products like our corn plastic “green” bottle will be less likely to end up in landfills or not decomposing in backyard compost piles. Next week, we’ll check back on our green bottle and discuss how much better it might (or might not) break down at an industrial compost facility.

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