Compostable materials can be used as a form of compost after they have decayed according to the Cambridge English dictionary. To be specific, compost is ‘decaying plant material that is added to soil to improve its quality.’
To be clear, in a regulatory sense, compostable and biodegradable are seen as being equivalent.
Given that they naturally break down into water, oxygen, and biological material, we can see how attractive compostable materials would be as production materials or, perhaps more likely, packaging as they can not only fulfil their initial use but also benefit the environment afterwards by becoming compost.
Which bioplastics are compostable?
PLA (polylactic acid) and CPLA (crystallised polylactic acid) are the two common compostable bioplastics which are made from plant starches in the form of glucose which is formed into polymers.
PHA is another compostable polymer which is made by converting food waste using bacteria.
What items and products are generally compostable?
Compostable bioplastic items created using the above polymers include many food applications as they are non-toxic and can handle up to 100°F temperatures:
- Shopping bags
- Single-use cups and lids
- Single-use cutlery
- Straws
- Food packaging, such as takeout boxes
A bonus is that if they do contain food residues it will not affect their ability to be composted!
How can I recognize compostable labels?
Not all compostable items can be composted at home (such as in your garden composter). If this is the case, you may see logos like these for industrial composting of food waste and compostable packaging etc:
If they can be composted at home in your garden, you may see this:
There may be others specific to your local area, so watch out for those!
What is industrial composting?
Assuming that a compostable bioplastic is completely eco-friendly is a little dangerous. If they are not composted properly, they will end up in landfill along with normal trash which is absolutely not green!
Many of these items require industrial composting which takes place in large municipal industrial composting facilities where food and garden waste, compostable bioplastics, paper, and wood are mixed, processed, and left in piles where after approximately 3-6 months they will have formed nourishing compost.
If it is available and can be achieved successfully it is a very green solution:
Industrial composting produces more than just high quality compost for soil remediation. It also produces jobs, a greener environment, enhanced food security, less waste, and less truck traffic hauling garbage. (Source)
However, if you do not have access to industrial composting it’s important that compostable bioplastics are not added to regular recycling as they will taint the batch and lead to all of the recycling heading to landfill or incineration.
Is there a standard for compostability?
Yes it’s the same standard as used for biodegrability, ISO 17088:2012 or Standards for Compostability BS EN 13432:2000 was developed in the year 2000 to help packaging users adhere to the European Parliament and Council Directive 94/62/EC of 20 December 1994 on packaging and packaging waste and outlines the ‘requirements for packaging recoverable through composting and biodegradation.’
Key BS EN 13432 tests and Pass / Fail criteria are:
- Disintegration – the packaging sample is mixed with organic waste and maintained under test scale composting conditions for 12 weeks after which time no more than 10 % of material fragments are allowed be larger than 2 mm.
- Biodegradability – a measure of the actual metabolic, microbial conversion, under composting conditions, of the packaging sample into water, carbon dioxide and new cell biomass. Within a maximum of 6 months, biodegradation of the test sample must generate an amount of carbon dioxide that is at least 90 % as much as the carbon dioxide given off from the control / reference material.
- Absence of any negative effect on the composting process.
- Low levels of heavy metals (Potentially Toxic Elements) and no adverse effect of the quality of compost produced. Upper limits, in mg/kg of dry sample, are: zinc 150, copper 50, nickel 25, cadmium 0.5, lead 50, mercury 0.5, chromium 50, molybdenum 1, selenium 0.75, arsenic 5 and fluoride 100.
- The composted packaging material must not have adverse effect on the bulk density, pH, salinity (electrical conductivity), volatile solids, total nitrogen, total phosphorus, total magnesium, total potassium and ammonium nitrogen characteristics of the compost. (Source)
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