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Compostable Plastics Research Update

Catch up with our latest research on the UK's system for compostable plastics in this webinar (broadcast 16/09/21). Hear from the UCL Plastic Waste Innovation Hub team about the latest results from the Big Compost Experiment and compostable teabag trials, life cycle assessment (LCA), labelling and behaviour, sorting technologies, microbial degradation work and public policy developments.


Maria Bawn - Chemistry, UCL

Jenny Bird - Policy, UCL

Charnett Chau - Life Cycle Assessment, UCL

Helen Hailes - Chemistry, UCL

Mark Miodownik - Materials & Society, UCL

Danielle Purkiss - Citizen Science, UCL

Nutcha Taneepanichskul - Mechanical Engineering, UCL

John Ward - Biochemistry, UCL

Chaired by Beth Munro, Institute of Making UCL

Notes: We really enjoyed the webinar! Unfortunately we ran out of time and we were unable to answer all questions live on the day. Here are some additional responses from the team:

Q: So were the teabags that didn't disappear actually compostable ?

A: Hi David, hopefully we answered this in our live response. We are carrying out controlled testing of the teabag brands people have tested via the BCE to formulate a better picture of teabag performance-I used the PGTips biodegradable bags with PLA in the glue

Q: Could you please let me know why compostable plastic bags and other items were allowed to be launched without any consensus and discussion with the actual stakeholders, such as the local authorities which are carrying the brunt of the mess that we are now into. Thanks. I need to know...I try to get our visitors to separate food the museum and gardens...not easy!

A: There are no rules saying they have to design things in consultation with local authorities, mores the pity. I agree, changing public behaviour is difficult. The public are currently faced with many different domestic waste systems and instructions depending on the local authority so there is no unified system they can get used to. We need to try and change that across the country.

Q: For council food waste collection - what actually happens to this?

A: It goes into anaerobic digesters…..this produces CH4 (methane) which can go into the natural gas grid and power electricity generation and then the residues left can be used as compost.

Q: I joined late so apologies if this was covered already, but how long do we think it will take to get widespread adoption of bio-based, compostable materials in packaging, and to align waste management systems so that any food based packaging is easily compostable everywhere in the UK?

A: Probably several years. The government was going to start to unify the waste collection and what happens to the waste, but then covid19 happened and I think the time scale for this has been removed.

Q: What evidence have you/will you collect about how viable it is to compost caddy liners in industrial composting facilities (i.e. after the bags have been used to collect food waste). Considering:
1. How fully the compostable caddy liners break down.
2. How long the liners take to break down (and whether this is quickly enough for the material they are composted in to then be spread to land).
3. Whether the compost left over after caddy liners have been comosted is safe to spread on fields (i.e. microplastics and other contamination is minimal)

A: Good question, but with the microbial consortia we develop, we could look at the caddy degradation- John and Maria. Yes, this is certainly one thing we need to look at and assess the degradation rates of biodegradable/compostable caddy liners with different conditions and different microbial inoculants. We are isolating many new bacteria from soils and composts for PLA degradation.

Q: Please can you share the independent evidence on the reported low contamination rates from the Italian system from academia or government.

A: Some industry reports covering Italian bio waste systems here;

Q: Your research is very aligned to WRAPS marginalised use of compostable packaging and this assumes that recycling will succeed for all standard flexible packaging used today. This is far from a reality today so would you consider including compostable food packaging such as produce bags, coffee packs, crisp bags, stand up pouches as these are solutions that we believe will be required?

A: Unfortunately there is a limit to the scope of our work we can carry out under our current NERC funding. Perhaps we should discuss with you how more work could be funded?

Q: Sorry, I was using 'chat' not Q&A , my mistake. But to summarise here... Will the LCA include 'non-target' end of life scenarios like littering which has been winding up the public ever since the dead blue planet whale back in Oct 17.

A: Yes, we will be looking to address littering and pollution as part of our LCA for compostables framework development.

Q: Do you see a relation between the level of degradation and the "quality" of the management of the compost bin (aeration, added quantities, daily/weekly, ...) ?

A: Presumably this is important- however I just lob everything in and stir from time to time and it manages to cope! Any material designed for home composting needs to be able to degrade under many different conditions of temperature etc.

Q: Do you know if there are any plans to increase the regulations on when something is accepted for home composting? As I understand, the mesh size to see whether a material is characterised as compostable is relatively large. Are there any plans to mitigate blends of compostable and not compostable plastics to be certified as compostable? To make sure we don’t get a build up of macro / micro plastics?

A: The UK Government has been consulting on regulation of compostable plastic and compost quality outputs from biowaste processes such as IVC and AD.

Q: I was positively surprised that a significant amount of tea bags were showing signs of biodegradation in home composting facilities. To my understanding these products are made of cellulose and PLA (for the heat sealability). PLA is not home compostable, only in industrial facilities. Did this study show that the PLA remained in the home compost ? Or did he degrade ? Thanks for this initiative, this is very great work

A: From Maria's examination it looked pretty well degraded by eye and we are following up studies on the microbes involved. The microbes able to degrade PLA appear to be present in variable quantities in different soils and composts. It needs some understanding of these first and their types and growth properties. We may in future be able to have special enrichment preparations where there are high numbers of PLA degrader, active at different temperatures and different conditions and market this for adding to home composts.

If you compost and want to take part in a home composting experiment, you’ll need:

  • a selection of identical compostable or biodegradable items (see list below)
  • a net bag and clip to securely close it (see guidance below)
  • a plastic milk bottle cap (or similar) and permanent marker pen to identify your items

If you do not use a composter but you're interested in finding out more, please see our Composting Processes page for more information.

1. Choose your experiment items

Select the type and quantity of compostable or biodegradable plastic items from our list that you would like to test. Please only select items that display the following manufacturer information:

  • 'compostable' (only)
  • 'home biodegradable'
  • 'home compostable'
  • 'suitable for home composting'
  • TUV OK Compost 'HOME' certification mark
  • Din Certco 'HOME COMPOSTABLE' certification mark

NOTE: If testing multiple items together please ensure they are an identical type and brand (one type and brand of item per net bag).

2. Prepare your experiment equipment

To make locating your experiment items in your compost easier, please compost your items in a plastic net bag (the kind of net bag used to hold fruit in a supermarket would be ideal). Use a permanent marker pen to identify your items on a plastic milk bottle cap (or similar) and add to your net bag. To test fruit and veg stickers please stick each label on a plastic milk bottle cap first then add to your net bag. Use a permanent marker pen to identify them. You will have the option to upload photographs of your composter and experiment equipment to help us analyse your results. See our Photography Guidelines for more information.

NOTE: Please ensure you use a perforated net bag. This is so a sufficient flow of oxygen, organic waste and microorganisms can come into contact with your experiment items.

3. Create a login account

Create a login account and share a few extra details about what composter you will be using for the experiment, its location in the UK for our Live Composting Map, and your composting method. Please set the duration of your experiment according to how long it usually takes you to make compost. There is the option to share photos of your composter and experiment items and equipment, if you wish. Please indicate on your form if you would like to share your images on the Big Compost Experiment website. See our Photography Guidelines for more information.

4. Start your experiment

Securely close the net bag containing your experiment items and identifying markers and add to your composter. Carry on composting as usual. We'll send you an email reminder when your experiment is due to finish and it's time to look for your net bag and items.

5. Submit your results

When your experiment timer has finished, please look for the net bag and items in your compost. You can use a trowel, spade or household sieve to locate it. Under 18s must be accompanied by a responsible adult. Check the contents of your net bag for any traces of your items. If there are any traces please compare them with our 'Scale of Degradation' in the results form in your login account and share any other useful observations about your experiment. There is the option to share a photo of your results. Please indicate on your form if you would like to share your image(s) on the Big Compost Experiment website. See our Photography Guidelines for more information.

NOTE: Once you have completed your experiment, please dispose of any item remains in your general waste collection. Check locally for recylability of other experiment equipment and rinse before recycling.

How to take a photograph of your experiment equipment

Pre- and post-composted items and equipment

  1. Place your biodegradable or compostable items on a clean surface alongside any secondary packaging (if applicable) and net bag. A contrasting surface is preferable (i.e. one on which the items will stand out).
  2. Orientate items and packaging (if applicable) in order to capture any compostable labelling or certification marks (if displayed). If testing multiple items together please ensure they are an identical type and brand (one type/brand of item per net bag).
  3. Position your camera approximately 1 metre above the objects. Position items clearly within the viewfinder of your camera or camera phone, so that all edges of items are visible. Please ensure no recognisable features (people, faces, house number, etc.) are visible in the image.
  4. Take a photograph (while keeping your hand steady!)
  5. Upload photographs via your login account, with the option to display them on our Gallery page.