Compostable materials… have been certified to break down completely into non-toxic components (water, carbon dioxide, and biomass) that will not harm the environment, given the right conditions – and within a certain timeframe, leaving no visible contaminants or toxic residues/substances. Some materials can decompose in your home compost but not all compostable materials are suitable for composting at home. For anything to be legally labelled compostable, it has to have been certified to break down in industrial (ie. local council) composting facilities within 180 days. The criteria for the industrial compostability of packaging are set out in the European standard EN 13432. EN 13432 requires the compostable plastics to disintegrate after 12 weeks and completely biodegrade after six months. For home composting, the OK certification is the most widely recognised – this requires at least 90% degradation in 12 months at ambient temperature. EN 13432 was adopted by the UK and other EU member states, which is why you may see it published as BS EN 13432. The ‘BS’ prefix is simply the abbreviation of ‘British Standard.’ It’s entirely possible to have a product which is compostable in practice, but meets no industry standards – this might be, for example, because it doesn’t do so within the defined timeframe.
The 4 characteristics tested for during EN 13432
Disintegration, namely fragmentation and loss of visibility in the final compost – this is measured in a pilot composting test (EN 14045) in which specimens of the test material are composted with biowaste for 3 months. After this time, the mass of test material residues has to amount to less than 10% of the original mass.
Biodegradability, namely the capability of the compostable material to be converted into CO2 under the action of microorganisms. The standard contains a mandatory threshold of at least 90 percent biodegradation that must be reached in less than 6 months (laboratory test method EN 14046).
Absence of negative effects on the composting process.
Amount of heavy metals has to be below given maximum values, and the final compost must not be affected negatively (no reduction of agronomic value and no ecotoxicological effects on plant growth).