Compostable plastics that are tested and certified according to the European standard for industrial composting EN 13432 are required to disintegrate after 12 weeks and completely biodegrade after six months. That means that 90 percent or more of the plastic material will have been converted to CO2. The remaining share is biomass, which no longer contains any plastic. EN 13432 also includes test on eco-toxicity and heavy metal contents to ensure that no harmful substances are left behind.
Very short composting cycles may not be sufficient to allow for a full disintegration of some types of biowaste as well as for some compostable plastic packaging. However, leftover scraps (usually ligno-cellulosics) in composting plants are sifted out and added to the next fresh compost batch for another composting cycle where they fully metabolise to water, carbon dioxide, and biomass.