Recycling Mystery: Compostable Plastics

After finishing off your morning coffee, you stop by the trash and recycling bins to dispose of your plastic cup. That's when you see the words "compostable plastic" printed on the side of the cup. Standing there, you can't help but wonder, "Which bin do I drop this in?"

Unfortunately, the answer isn't so simple. Compostable plastics are designed to biodegrade into soil conditioning material, also known as compost. The best way to dispose of compostable plastics is to send them to an industrial or commercial composting facility where they’ll break down with the right mixture of heat, microbes, and time. If this type of composting facility isn't available in your area, the only other option is to throw them in the trash.

Compostable plastics are typically made from some type of renewable raw material. Corn starch is one of the most common materials, but there are many other options. Regardless of what compostable plastic is made from, it's transformed into a polymer that looks and feels like traditional plastic.

The American Society for Testing and Materials (now known as ASTM International) has published specific guidelines that must be met for a material to be labeled as commercially compostable. In broad terms, those guidelines are:

Compostable plastics can be difficult to recycle. They require commercial/industrial composting facilities. Not all recycling facilities have these composting capabilities.

If your city or county runs a composting program, they may accept compostable plastics, but don't assume they accept them. In many instances, composting facilities will filter out any trash, including compostable plastics because of a lack of sorting sophistication.

Outside of looking closely at the label, there's no easy way to separate compostable plastics from regular plastics that someone mistakenly dumped in their compost bin, so facilities will just pull out everything that looks like trash and send it to the landfill or burn it. Call and ask your local recycling coordinator if the local compost facility accepts compostable plastics specifically.

If they do not or you don't have a composting facility in your area, the only other real option is to throw it in the trash. Because compostable plastics aren't the same as traditional plastics, they shouldn't be thrown in with your general recycling. As systems improve, compostable plastics can complete their lifecycle as compost.

Use of compostable and biodegradable plastics has grown significantly over the previous decade. Unfortunately, there are still many questions and concerns about this material. Below are some of the most common questions we receive about compostable plastics.

Unfortunately, most backyard compost piles don't get nearly hot enough to compost these plastics. Not only do they require high heat, but they also need that heat for a sustained period of time. In many cases, even some industrial or commercial compost facilities don't stay hot for a long enough period of time to fully degrade the plastic.

In many cases, the manufacturer will make it quite apparent that the material is made of compostable plastic, but there are two "official" ways to distinguish a compostable plastic from a regular plastic.

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