A key aspect of a circular economy in Scotland is the separate collection and treatment of food waste through anaerobic digestion and in-vessel composting to produce a high quality fertiliser that can be used in agriculture. This will help Scotland achieve ambitious climate change targets both directly, by reducing the amount of methane emissions by diverting food waste from landfill, and indirectly by locking carbon and nutrients into the soil which also helps with drought resistance and improves soil health and crop growth.

To help tackle the global issue of plastics pollution and ensure that soil quality is protected through the use of food waste derived compost and digestate, SEPA will be amending its position on plastic contaminant limits allowable in compost and digestate outputs. From the 1st December 2019 the plastic limit for outputs will be reduced to 8% of the PAS110 limit for digestates and 50% of the PAS100 limit for composts. SEPA’s approach to reducing plastic contamination from compost use in the environment leads the way in the UK and is comparable with the leading EPAs in the world on this issue.

The purpose of this project was to research plastic contamination in domestic (from local authority household collections) and commercial food waste received at composting sites and make recommendations for improvement. The project also reviewed practice globally to help both develop and support the recommendations.

SEPA, through the commissioning and publication of this report, recognises the challenges faced by compost operators and the role the whole supply chain has in reducing plastic contamination. The hope is that this report improves knowledge of the issue across the supply chain and helps compost operators achieve compliance with the stricter limits with support from the supply chain.

The final report is available on our website here.

About the research:

Domestic and commercial food waste was sampled from Scottish composting sites and analysed to determine the amount of physical contamination present. The method of presentation was also recorded- whether in a compostable or non-compostable liner. Although the overall contamination was relatively low (<10%) the analysis showed that it would be very difficult to produce a final product that is able to achieve the quality standard (PAS100) or SEPA’s new regulatory limits (50% of the current quality standard level) based on the current levels of feedstock contamination. It is clear that further work is necessary to reduce the amount of contamination at source, both for commercial and domestic food waste.

Key findings

Feedstock with 5%, or even 1%, of contamination requires significant clean-up if the final compost is to achieve either PAS100 or the new regulatory limits. In short, achieving such reduction levels is extremely difficult. Contracts between producers/collectors and treatment facilities should ensure that the amount of contamination does not prevent the site producing a high quality material.

The results provide a strong indication that provision of compostable caddy liners by local authorities leads to lower plastic contamination (both in terms of the bag itself and the contents of the bag). This supports previous research in this area.

If we want to tackle the global plastic pollution problem and protect our soil and use the valuable nutrients in compost and digestate we need to make sure the input material is as clean as possible. SEPA has published guidance on food waste management in Scotland which sets out our expectations across the supply chain.

Next steps:

Whilst not all of the recommendations in the report will be taken forward, we will continue to work with key stakeholders to develop a package of actions to tackle contamination at source.