Biodegradation

From Green Plastics

Biodegradation is a process where something breaks down into simple compounds as a result of the action of microorganisms (like bacteria, fungi, or algae). The term biodegradation is actually a contraction, short for "biotic degradation." Something is biodegradable if it can be broken down by this kind of process.

In order to say that something "biodegrades", it therefore has to meet the following requirements:

1. it has to break down (this is simply "degradation")
2. it's molecules have to break down from complex molecules into simpler ones (this is "chemical degradation")
3. the breaking down of its molecules has to be accomplished by microorganisms.

In order to prevent misinformation in advertising, standards organizations have made even more strict requirements for something to be labelled as biodegradable. In addition to the above list, something can only be labelled as "biodegradable" if:

1. the biodegradation of the material has to be scientifically measurable. Since most biodegradation produces CO2 as a by-product, usually this is measured by the amount of CO2 produced.
2. the biodegradation of the material has to be fast enough to have a significant effect in a reasonable amount of time. For example, the ISO standard requires 60% biodegradation within 180 days for a material to be called biodegradable; the Europenan Norm EN13432 is more strict, requiring 90% biodegradation within 90 days.

Types of Biodegradation

Because biodegradation requires microorganism to do something to a material, usually the material has to be broken up into smaller pieces first. As a result, most biodegradable materials become biodegradable after the action of another kind of degradation.

Hydro-biodegradable

Hydro-biodegradable materials are first broken down by interaction with water (a process called hydrolysis), and then are further broken down by microorganisms.

Photo-biodegradable

Photo-biodegradable materials are first broken down by interaction with sunlight (a process called photolysis), and then are further broken down by microorganisms.

Oxo-degradable

Some companies have been claiming that they have created an additive that can be added to traditional plastics to make them biodegradable. These products become what is called oxo-degradable, and sometimes is incorrectly identified as oxo-biodegradable.

Although this allows the plastic to return to the environment, these products are not biodegradable. Instead, the additive allows the plastic material to break down physically when exposed to water, into pieces small enough to be accidentally ingested by microbes. However, the microbes are not able to actually break this material down further. The end result is therefore a material that combines biomass with polymer residue. The plastic never decomposes as a result of interaction with the organisms. This process is therefore more accurately called "disintergration" rather than "biodegradation".