Firstly, here is a quick definition of the two different kinds of waste:
- The term biodegradable is chiefly defined as “susceptible to decomposition by living organisms”. The organic matter here is broken down by microorganisms - bacteria, fungi to carbon dioxide (CO2).
- Composting, on the other hand, is "human-driven". While material "biodegrades" during composting, the process is accelerated by human management.
The difference between the two terms is further complicated as both words are often used as synonyms. However, the terms do not mean exactly the same things. "Biodegradable" waste should be broken down into mostly CO2 (water, CO2, and bio-mass). However, the length of "biodegradation" is dependent on many parameters (temperature, humidity, etc.). Biodegrading thus has varied impact on the environment.
On the other hand, "Compostable" plastics are a subset of "biodegradable" plastic and have to be certified by a third-party to adhere to international standards, namely, ASTM D6400 (in the U.S.) or EN 13432 (in Europe) in special facilities. Hence, while all "compostable" waste is "biodegradable", not all "biodegradable" waste is "compostable". "Compostabe" waste degradation also varies depending on approach. Anaerobic composting creates methane. Methane is 26 times more potent than C02 and is much more significant as a contributor to greenhouse gas emissions. Composting can also be an aerobic process, during which, no methane is produced. Thus, composting effects and impact on the environment depend on the approach taken.
There are many considerations when discussing whether "biodegradable" waste is better than "compostable". Read more about these reasons: