Difference Between Biodegradable & Compostable

Biodegradation and composting are often used to mean the same thing: breaking material down so the organic matter it contains can be salvaged and reused. Biodegradation and composting are both caused by the action of heat, moisture, exposure to ultraviolet light, and the presence of microorganisms in the environment. They are similar processes, but there are differences.

Natural Versus Processed Materials

• One of the significant differences between them is that "biodegradable" is the term applied to breaking down materials that have been processed, while "compostable" relates to naturally occurring substances such as grass cuttings, leaves or vegetable peelings. Composting occurs naturally, wherever there is plant life.

Timescale

• One major difference between them is the timescale of the degradation process. Biodegradable materials can take months or even years to break down whereas compostable materials can take as little as three or four weeks. The speed of decomposition depends on the organic content of the material and on the environment.

Plastics

• Another difference is that some materials, particularly certain types of plastic, require industrial composting to break them down because of the high temperatures needed for the process to occur. Organic materials degenerate at much lower temperatures, as seen in any backyard compost heap.

Bacteria

• According to the the American Society for Testing and Materials, as published on the online magazine Packaging Knowledge, a material is only considered to be biodegradable if "the degradation results from the action of naturally-occurring micro-organisms such as bacteria, fungi, and algae."

  For plastics to be considered compostable under this definition, they must break down into biomass, carbon dioxide and water at the same rate as paper. They must not produce any toxic material and must be able to support plant life.

Products

• In recent years the plastics industry has developed products made from organic materials such as corn, potato, cellulose, soy and sugar to overcome problems caused by nondegrading oil-based plastics.

  Other industries are doing likewise, with many biodegradable products now available. The New York-based Biodegradable Products Institute promotes the use and recycling of biodegradable plastics via composting and has set criteria that manufacturers must meet to gain its accreditation.

Landfill

• There are some disadvantages to biodegradable waste, particularly if dumped at landfill sites. The bacteria needed for decomposition cannot survive in the airless, moisture-free environment which landfill sites are required by law to maintain. Environmentally dangerous methane gas is generated as the waste breaks down without air. Toxins also accumulate, possibly including heavy metals and pesticides.

  So another significant difference between biodegradable and compostable materials is that the former are only "green" up to a point because of the risk of methane and toxins. Composting, if correctly done, does not have these drawbacks.