By K. Flowers
Compostable is a very carefully controlled term. It is not as prone to the greenwashing that the word biodegradability experiences. Materials can be composted in two ways: home or industrial. The requirements are different, and these are outlined below.
To be a certified home compost, the compost that is made, must go through 6 tests.
Home Composting Certification
1. Material understanding – the material should not contain high levels of certain metals – the ones set out in the standard. The levels of these elements cannot be too high if the material is to be added to healthy soil.
2. The material should disintegrate if left to degrade in compost at room temperature within one year. It is important what the material disintegrates into – the fragments themselves can be harmful and the material should be designed so they are not.
3. The material should be biodegradable when tested, i.e., the material should be broken down to gas, water, and biomass within 6 months.
4. The compost made from the material should not be harmful to plants.
5. The compost made from the material should not be harmful to earthworms.
6. The compost made from the material should be easily recognised as such – even by a non-specialist.
A material might pass some of these requirements and be labelled as biodegradable, but this doesn’t mean that it can be broken down to produce a quality compost that people would love to use. It could be that a material may easily breakdown, but the compost may not look or feel natural or that what it breaks down to is harmful.
A variation to the certification outlined above is used to see if the material could be composted using industrial composting. Home composting is normally at room temperature and industrial composting is done at 58°C. The extra heat adds a lot of energy that can assist with breaking the material down – some materials are very vulnerable to heat breakdown so perform well in this test. A material that does well in home composting, will be expected to do well in industrial composting.
In the certification of industrial composting the requirement that the compost mustn’t harm earthworms currently doesn’t feature in the list of requirements.
Figure 1: Industrial scale composting
Industrial Composting Certification
1. Material understanding – again, the material should not contain high levels of certain metals – the ones set out in the standard.
2. The material should disintegrate if left to degrade in compost at 58°C within 3-6 months. (Figure 1). Again, it is important what the material disintegrates into – the fragments themselves can be harmful.
3. The material should be biodegradable when tested, i.e., the material should be broken down to gas, water, and biomass within 6 months.
4. The compost made from the material should not be harmful to plants.
5. The compost made from the material should be easily recognised as such – even by a non-specialist
A supply chain with materials that can be certified as industrial compostable will be able to claim that their products can be put into municipal composting to produce a healthy soil additive. Likewise, a home composting certification means that the product can be thrown into the composter at home, and it will breakdown – of course it is important to make sure that the whole product passes the certification or the bits that won’t pass will be left behind in the compost.
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