Biodegradability and Compostability
by Lauren Olsen Zero Waste Manager at World Centric
A material capable of undergoing biological decomposition in a compost site as part of an available program, such that the plastic is not visually distinguishable and breaks down to carbon dioxide, water, inorganic compounds, and bio mass, at a rate consistent with known compostable materials (e.g. cellulose) and leaves no toxic residue.
In order for a plastic to be called compostable, three criteria* need to be met:
- Biodegrade – break down into carbon dioxide, water, biomass at the same rate as cellulose (paper)
- Disintegrate – the material is indistinguishable in the compost, that it is not visible and needs to be screened out.
- Eco toxicity – the biodegradation does not produce any toxic material and the compost can support plant growth.
*From American Society for Testing and Materials (ASTM).
Plastic which will degrade from the action of naturally occurring microorganism, such as bacteria, fungi etc. over a period of time. Note, that there is no requirement for leaving “no toxic residue, and as well no requirement for the time it needs to take to biodegrade.
Plastic which will undergo a significant change in its chemical structure under specific environmental conditions resulting in a loss of some properties. Please note that the is no requirement that the plastic has to be degrade from the action of “naturally occurring microorganism” or any of the other criteria required for compostable plastic.
A plastic therefore may be degradable but not biodegradable or it may be biodegradable but not compostable (that is it breaks down too slow to be called compostable or leaves toxic residue).
Composting in Hawai‘i
Here in Hawai‘i we do not have a composting facility. We have a landfill that mostly takes construction material. H-power is where Punahou’s waste goes, H-power burns mostly green waste, pre-consumer food scraps, post-consumer food waste, compostable fiber products and compostable plastics by burning it and converting into energy.