Compostables

Definition

Composting – and compostable materials – refers to the ability of plant or bio-based materials to be converted into nutrient-rich soil or humus through decomposition by natural microorganisms. Composting is a form of natural recycling that uses the processes of decay and growth to take carbon from leaves, trees, plants or animals and return it back to the earth.

Principles

The process of composting generally refers to activity that is initiated and managed by humans. The term ‘compost’ refers to soil material created from organic by-products or waste that has naturally decomposed or broken down into its basic chemical elements. While all compostable materials are biodegradable, not all biodegradable materials are compostable, and manufactured materials labelled as bio-based should not automatically be assumed to be compostable. 

Under the correct conditions of heat and moisture, compostable materials will break down within a certain period (usually months), and release nutrients back to the earth. In contrast, biodegradable labelling rarely clarifies a timeframe for decay and is not sufficient as an environmental accreditation of a manufactured material or product.

Although compostable materials such as paper packaging might readily degrade in the natural environment, compostable materials such as bioplastics don’t necessarily break down in landfill, water or domestic compost. Manufactured materials labelled as compostable must therefore adhere to a regulated standard or certification, and decompose under specified conditions.  

Implementation

At present there are two compostable categories for manufactured goods, predominantly relating to materials in the packaging sector: industrially compostable and home compostable. Other specifications such as UK PAS 100 refer only to composting procedures that ensure resulting composts are certifiable, traceable and safe.

Industrially Compostable The Seedling and OK Compost logos both indicate that a material has been certified compostable according to the European EN 13432 standard, achieving 90% biodegradation in less than six months. Similar compatible standards exist for other global regions such as ASTM 6400 in America and GreenPla in Japan. If an item is labelled as compostable, then it should be considered as industrially compostable only.

Home Compostable Although home compostability standards such as EN17427 are still in their infancy, the more established OK Compost Home or Din Certco Home Compostable certification marks are frequently encountered on packaging to certify shorter composting periods under temperatures of between 20-30ºC. 

In 2023, University College London (UCL) ran a citizen science project testing home compostable materials such as cups, bags and magazine wraps, and found that even items labelled as ‘home compostable’ failed to fully decompose in the majority of cases. The project concluded that compostable materials and testing regimes need to be improved to better reflect the variety of home composting conditions.¹ Campaigners and manufacturers have also been pushing for compostable standards in other sectors such as the textiles industry, where the world’s first specification for compostable textiles has now been accepted for development in Australia.²

End-of-life

With the exception of products labelled as ‘home compostable’ or in instances where manufacturer take-back schemes exist, compostable items need to reach the correct industrial waste stream to avoid being incinerated or sent to landfill. 

Although many local authorities in the UK accept food waste as part of a separate collection stream, domestic materials labelled as compostable tend to be excluded. This is because industrial composting facilities typically turn-over organic waste in a matter of weeks, whereas standards for compostable materials specify that periods of up to six months are needed to achieve certified degradation. Therefore, landfill and incineration still remain the most likely destination for many compostable packaging materials such as bioplastics.³

Limited studies suggest that public perceptions about whether an item is compostable or biodegradable can lead consumers to overestimate the degradation capabilities of a product or material, viewing the product labelling as a technical solution that removes responsibility from the individual – as concluded by UCL; ‘Although people are attracted by the idea of compostable plastics, they are confused about appropriate disposal routes. In particular, the distinction between items that are suitable for home composting versus those that require industrial composting is lost on many people’.⁴

End of life challenges lie as much with processing infrastructure and lack of consumer guidance as with the materials themselves. For instance, enabling closed-loops systems at large events or venues offers a model for the disposal of used compostable packaging, as the packaging and food waste can be composted together in a single stream, without separation.

Inadequate infrastructure and lack of clear labelling or disposal instructions mean much more effort is still required to ensure compostable materials are correctly disposed of. These might include EPR (Extended Producer Responsibility) schemes, clearer labelling standards, improved local and international governance of waste processing, and improved education and guidance for business and consumers.