In the world of recycling, there are several terms that can be difficult to break down (much like certain types of plastic).
Two of the most commonly used phrases are biodegradable and compostable, but many people don’t understand the fundamental differences between the two.
This can cause confusion when it comes to figuring out whether to throw used plastic products away in the recycling bin or trash can.
In short, the difference between the two terms is that biodegradable products deteriorate naturally over time, while compostable items require a specific environment to become compost, but break down more quickly and can often be recycled and reused.
What Does Biodegradable Mean?
Whether it takes a month or a millennium, everything we manufacture will ultimately disintegrate into dust and return to the natural elements. When defining which of these substances are biodegradable, scientists and public health officials often ask a few main questions:
- Did the object come from nature?
- Has it undergone an excessive level of artificial modification or processing?
- What are the conditions necessary for deterioration to occur in what they consider to be a reasonable amount of time? Does the object have a positive or neutral impact on an ecosystem?
Biodegradable materials are defined by the American Society for Testing and Materials (ASTM) as anything that degrades from the action of naturally occurring microorganisms, such as bacteria, fungi and algae. Usually, products that are derived from plants, animals, or natural minerals are biodegradable.
Objects that are defined as biodegradable extend far beyond plants and food, however. Items like paper and cardboard boxes can also be classified as biodegradable products, even though they will take much longer to break down to a microscopic level.
You could even argue plastic is biodegradable because it eventually breaks down, but this process can take centuries. These substances will eventually decompose into carbon dioxide, water and other forms of organic material.
An apple, on the other hand, is something we can all agree on. For something like an apple, this process would most likely take a few months.
What Does Compostable Mean?
Think of biodegradable as an umbrella term and compostable as a term underneath it. Here’s what scientists and public health officials ask when defining compostable materials:
- Can the material transform into organic waste that is useful for the environment?
- Is the compostable material a type of food or organic substance to start with?
- How long will it take for the material to decompose, and can it compose in a timely manner?
Composting is a form of biodegradability that transforms organic waste — such as food scraps and fallen leaves — into humus, a dark brown material that can supply soil with valuable nutrients. Unlike many biodegradable materials, compostable products are useful to the environment. If you want to try composting at home, check out our guide.
Homeowners can also utilize their own backyard compost pile and recycle organic waste to create a soil conditioner. The resulting compost will improve the structure of soil, helping it retain water and nutrients. All in all, these efforts add up to create a world that is more sustainable and better for everyone.
The specification ASTM D6400 refers to compostable products that can be processed in municipal or industrial composting facilities, drawing the line between products that can be broken down or composted and biodegraded. ASTM D6400 was specifically made to identify plastics that are compliant with these standards.
According to this ASTM certification, biodegradable materials should disintegrate within 12 weeks and biodegrade at least 90% within 180 days in a composting facility. Approximately 10% of solid material should be left at the end of the six-month-long process, either as compost or biomass and water.
Understanding the Difference Between Biodegradable and Compostable Plastics
There are certain types of plastic products that are biodegradable and compostable. For example, at Public Goods we produce compostable plastic waste bags by working with Polyethics Industries, a BPI-certified manufacturer.
These types of products are made using hydrolyzable polymers, chemical compounds that degrade over a period of time when they come into contact with water, a key ingredient in composting. Unlike other types of plastics, they break down into elements the soil can absorb, and the process takes less than 180 days, not more than 1,000 years.
Composting facilities and industrial companies recycle these plastics by enveloping piles of compost under tarps at temperatures of more than 50 degrees Celsius (that’s roughly 122 degrees Fahrenheit). After about 150 days it becomes useable. Depending on the type of product, the facilities sometimes add warm water with a nutrient mixture to accelerate the decomposition process.
Do not try composting these plastics in your home. It’s much easier to donate them to the proper facilities.
It’s also worth mentioning the difference between bioplastics, biodegradable plastics and oxo-degradable plastics.
Bioplastics are made from non-toxic organic materials like corn starch, and will typically break down in a few weeks without releasing toxins into the soil or water. However, bioplastics shouldn’t be left to break down a landfill, as this waste yields methane gas during the biodegradation process. Instead, these plant-based materials should be taken to a commercial composting facility to biodegrade properly.
Biodegradable plastic is chemically different from bioplastics, as they are petroleum-based and mixed with an additive that makes the biodegradation process happen much faster. Sometimes the two plastic types are conflated with one another, but the distinction is important.
Finally, there are plastics classified as oxo-degradable, which mimics biodegradation but actually remains in the environment for indefinitely. Oxo-degradables are made from a conventional plastic mixed with an additive, which causes the plastic to fragment into microplastics. However, the degradable products do not break down at molecular level, therefore leaving the microplastic waste behind until it fully breaks down.
The Different Labels to Look Out For
Food and similar organic substances are inherently compostable, but the situation is not so simple for other products.
The Compostable Label
The Federal Trade Commission [FTC] allows brands to label their products compostable if ‘‘all the materials in the product or package will break down into, or otherwise become a part of, usable compost (e.g., soil conditioning material, mulch) in a safe and timely manner in an appropriate composting program or facility, or in a home compost pile or device.’’ In this case “timely manner” means at the rate of the surrounding materials in the compost pile.
The Biodegradable Label
When it comes to claims of biodegradability, the FTC stated that products should fully decompose within one year of disposal. Some of these products are compostable, even if they don’t carry that claim. If you are into composting, conduct some research on a case-by-case basis.
Companies that want to further substantiate the claim that they carry compostable products can seek certification from the Biodegradable Products Institute [BPI]. The BPI certification rules were written for people in the industry, not consumers. Nonetheless, we did find a code with a requirement that is relatively easy for everyone to understand: 90% of carbon in an item needs to be disintegrated within 180 days.
Biodegradable products may not be compostable, but they are still valuable to the environment. They may not be giving as much back to the earth, but at least they are taking up less space in landfills.
Your Knowledge of Biodegradability Can Make the World More Sustainable
If you want to reduce the amount of waste that rots for decades in a landfill, the first step is to buy eco-friendly goods and products that are biodegradable (preferably compostable, too). Here are a few examples of sustainable products from Public Goods (completely biodegradable and compostable, including the packaging):
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