Q: What is the difference between biodegradable plastics and compostable plastics?
A: Plastic that is compostable is biodegradable, but not every plastic that is biodegradable is compostable. Biodegradable plastic may be engineered to biodegrade in soil or water, whereas compostable plastic refers to biodegradation into soil conditioning material (i.e., compost) under a certain set of conditions.
In order for a plastic to be labeled as commercially “compostable,'' it must be able to be broken down by biological treatment at a commercial or industrial composting facility. Naturally, composting utilizes microorganisms, heat and humidity to yield carbon dioxide, water, inorganic compounds, and biomass that is similar in characteristic to the rest of the finished compost product.
Decomposition of the plastic must occur at a rate similar to the other elements of the material being composted (within 6 months) and leave no toxic residue that would adversely impact the ability of the finished compost to support plant growth. ASTM Standards D6400 and D6868 outline the specifications that must be met in order to label a plastic as commercially “compostable”. There are currently no ASTM standards test methods in place for evaluating the ability of a plastic to compost in a home environment.
Simply put, while they are labeled compostable, most takeout boxes, plates, and other dishware will only decompose in highly controlled industrial facilities. The compostables that look like plastic or that are coated with bioplastics are mostly made out of corn, and we ask that you do not add those to your bin.
Compostable items made out of fiber (such as bagasse, palm fiber, wood fiber, etc) or the ones that look more like paper will more easily decompose in a traditional composting pile. If you want to include a small quantity of these items in your bin, we suggest that you tear them into smaller pieces before adding them to help them decompose a bit faster.