Recycling Mystery: Compostable Plastics

biodegradable plastic bowls and plates
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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.

What Exactly Is Compostable Plastic?

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:

  • “It must able to be broken down by biological treatment at a commercial or industrial composting facility”
  • “Decomposition of the plastic must occur at a rate similar to the other elements of the material being composted (within 6 months)”
  • “Leave no toxic residue that would adversely impact the ability of the finished compost to support plant growth”
Repurpose 100% compostable plant-based insulated hot cup and lid set

Manufacturers typically make compostable plastics from renewable materials, like these Repurpose brand cups, which are corn-based. Image: Amazon

How Do I Dispose of Compostable Plastic?

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.

Other Common Compostable Plastic Questions

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.

Can I Put Compostable Plastics in a Backyard Compost Bin?

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.

compostable labeling

Look for the compostable label from the Biodegradable Products Institute or the number 7 recycling symbol with “PLA” underneath.

How Can I Tell if a Plastic Is Compostable?

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.

  • The first is to look for the certification label from the Biodegradable Products Institute. This organization certifies that products are able to be composted in commercially run composting facilities.
  • Another way to tell is to look for the plastic recycling symbol. Compostable plastics fall into the catch-all category marked by the number 7. However, a compostable plastic will also have the letters PLA underneath the symbol.
 

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Brian Brassaw

Brian Brassaw

Brian formerly managed the Earth911 Recycling Search and shared green living tips and tricks on Earth911’s Instagram, Pinterest and Twitter accounts. Brian also shares DIY projects on Little Pilots Lounge.
Brian Brassaw

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