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Compostable Plastics Research Webinar

Watch this public webinar to hear about the latest research on compostable plastics from the UCL Plastic Waste Innovation Hub (broadcast 24/11/2020). We present the first year of results from our nationwide Big Compost Experiment citizen science project on home compostable plastics; discuss our policy recommendations on compostable plastics for the UK Government; and discuss our collaborative research programme on compostable plastics for the next 3 years. With Q&A discussion.

Mark Miodownik - Professor of Materials & Society, UCL
Helen Hailes – Professor of Chemical Biology, UCL
John Ward – Professor of Synthetic Biology for Bioprocessing, UCL
Jenny Bird – Public Policy Manager, UCL
Danielle Purkiss – Research Associate, UCL

Beth Munro - Research Manager, Plastic Waste Innovation Hub / Institute Of Making, UCL


-Due to a 'technical hiccup' the first 2 minutes of Beth's introduction has not been recorded unfortunately. Sorry Beth! It was great!

-Additional webinar Q&A responses below

Q: This may be too simple a question but: how can we be certain the plastics are broken down to elements & not just to particles large enough to cause problems but too small to remove & reuse?

A: In our project we will be looking at the biofragmentaion i.e. breakdown into the molecuar fragments by chemical analytical methods, as well as the biodeterioration, which should provide us with this information.

Q: So there is a case for saying that composting - given all the beasties found - is integral to increasing biodiversity?

A: Yes, it certainly is. Composting is going on around us in the natural world all the time. When any plant dies or leaves fall in the Autumn, the process of decay and recycling by soil organisms starts and this returns a lot of the carbon and other elements to the soil. Because this is the natural food for millions of different organisms in the soil it maintains the biodiversity in the soil. When humans do their 'composting' they are doing the same process in a slightly more contained and controlled way but the final outcome is similar. The composted material is converted to humus which is a complex mixture of fixed carbon, microorganisms, trace elements and can be used in gardens to fertilise the soil and add to the soil structure and diversity.

Q: Have you consulted with "hard core" gardeners? Gardeners world often say minimum of 12 months to get good quality compost (for your garden, independent of compostable plastics) - so the 12 month timescale for the home composting test may be realistic; may be a need to educate consumers how best to compost.

A: Yes, in a garden with the cycle of season and temperature it does take a good 12 months (I have often a cycle of 18 months or more) to leave one heap or bin to fully mature. It’s all to do with temperature and if on is still adding material to the top. Once plant or food waste is stopped being added, 12-18 months is common. This includes a winter and all microbial activity slows down to a very slow rate in the winter. Using a hot composting method speeds this process up considerably.

Q: Do you also see problems with people putting compostable plastics into recycling bins? Labelling is part of the problem - it's inconsistent.

A: Yes, if compostable plastic gets into the plastic recycling waste stream, it contaminates the final product. No one wants a recycled waterproof plastic sheet that rots away when it rains.

Q: What value does compostable plastics add to a compost/digestate? Or is it just a disposal route for the material?

A: Ultimately biomass if degraded. A compostable plastic such as PLA is a polymer that provides a food source for soil microbes so just like the polymer cellulose (a polymer of glucose) the biopolymer packaging is converted to soil biomass. PLA is made from lactic acid which is the tasty acid made by lactobacillus and other bacteria and is found in all those fermented foods such as kimchi, yogurt and many fermented dairy products, saurkraut, fermented fish products and many other fermented foods. Many soil microbes will eat the lactic acid (like we can) and use it to grow, thus increasing soil diversity.

Q: Can you put a figure on how much carbon is sequestered per kg of compostable plastic?

A: It would depend on the composition of the plastic but 30% of CO2 is returned to the atmosphere by composting compared to 100% by incineration.

Q: Lets face it - humans are lazy. This needs to be bombproof. Perhaps all packaging should be collected and composted industrially. I am a keen gardener and struggle to know whether things can go in my compost, I’d rather not experiment in my organic compost tbh!!!

A: Yes, simpler is better and it would be great to get a completely uniform collection and recycling system across the UK and having this a simple as possible.

Q: Did anyone put a large amount of these materials in a composter at same time to see if that had any impact on composting rates?
A: I don’t know if anyone deliberately did this, but it’s the kind of experiment that we can consider in the new grant that we have.

Q: I'm sure that this is a given, but is this project being framed in the context of the EMacA Butterfuly Diagram (from the perspective of the materials arising) or from the UNEP Circularity Diagram (from the perspective of the user) or both?

A: Not sure what you mean by this. There are diagrams on this site - https://www.ellenmacarthurfoun... that would be the kind of circular system that we would aspire to.

Q: If you don't put kitchen waste (i.e, vegetable peelings, etc) only garden cuttings, weeds etc, in your home compost, does that have any bearing on how fast or well plastics will decompose?

A: This is an interesting question and one that should be investigated. I presume you mean bioplastic. I would think that food waste will encourage faster growth of microorganisms that should mean that the bioplastics could be degraded faster, especially if the rapid degradation of the food waste means a temperature rise.

Q: Should we still be calling them plastics if they are from biomass?

A: Bioderived plastics is the best description as they are being used as plastics.

Q: What other items are out there that are similar to many teabags in that they are considered compostable but contain small elements that are actually not compostable? What are the risks of contamination if more and more products are diverted to composting?

A: Some items such as sandwich/food boxes are more obviously multi material packaging (plastic window, card box etc), others are less obvious and harder to identify such as oxo-degradable plastic packaging. Tighter regulation of multi material packaging is needed to ensure all constituent parts are compostable if disposed of together. There is much evidence to suggest oxo-degradable plastics have negative environmental impacts (and impacts on existing waste and recycling streams) and should be banned

Q: Do you think it would be good for companies to state how long it will take for their product to biodegrade so we have a clearer standard?

A: Yes, but they would also have to define the conditions for their definitions e.g. ' at a constant temperature of xxx.' Or 'in a normal composting cycle'

Q: Do we know how much CO2 is produced by these products degrading?

A: An answer above has this: approx 30% in composting vs 100% conversion to CO2 by incineration. Remember that all plant material that composts in the wild returns some CO2 to the atmosphere as the microbes grow and digest the cellulose. Just like us they eat the plant material, leaves, food waste, bioplastic and some is converted to biomass (more bacteria) and some is breathed out as CO2 and water.

Q: Interesting to know guide for product manufacturers intending to using biodegradable. Could anyone share the link please?

A: useful guide from WRAP

Q: What is going to be legally enforceable and will the government also be legally responsible? What would be the penalties for failure to meet targets?

A: The government is planning to set itself a legally binding long-term target in the area of resource efficiency and waste reduction. There will be a new environmental watchdog (the Office for Environmental Protection) whose job it will be to report each year on progress towards the target. The government will be required to report to Parliament each year on whether it is on track to meet the targets. If it is not, they must set out plans on how it will close the gap. This is the same approach that is used for the existing long-term legally binding target to cut carbon emissions.

Q: In relation to environmental impacts, what will you be looking at? For example, will you be considering impacts on soil, and soil organisms, food grown in soil to which composted packaging has been added, impacts downstream/in the sea? Also, will you be investigating any differences in impacts between starch-based and other packaging?

A: We will be looking at the changes to the microbial composition during and before and after the breakdown in soil. We don’t have the resources in this grant to look at food. There was another grant that would have looked at this but that wasn’t funded!

Q: Given that not all my actual garden waste composts very efficiently I doubt the (harder to compost) biodegradable packaging will compost well. Answer has to be industrial processing. Key to that as you say is labelling, collection and waste processing.

A: Industrial composting is carried out at a higher temperature so it does degrade many things that take ages in a home compost heap or bin.

Q: For me there is a difference between biodegrading and composting. Composting produces compost which is good for improving the soil, it’s not the same as biodegrading.

A: In the context of what is actually happening in a compost heap the two words mean the same. Biodegrading means the breaking down of something by a biological process. Exactly what is happening in a compost heap where microorganisms are doing the degrading (breaking down the plant material and assimilating this into their cells). When we talk about things beyond a compost heap we tend to say biodegrading as it can be a general term for the biological breakdown of anything e.g. the biodegradation of a dead mouse on a forest floor is the normal recycling by nature but we normally wouldn’t call it composting which is more of a human activity.

Q: Will there be dialogue with DEFRA / EA about waste code exemptions in a world where new materials are introduced into compost waste streams?

A: We plan to engage with DEFRA about what would be required for a sustainable system. This will include discussion of relevant standards and regulations.

Q: Are any toxic products produced or looked for in the degradation of plastics?

A: With bioplastics the material should compost down to natural materials. For other plastics (polyethylene, polystyrene etc) there are no real biological routes in sensible timescales. So these are there for a long term in the environment.

Q: Does the production and biodegrading of these plastics use alot of energy? Will you be looking at not using plastics at all. eg the plastic cover to cucumbers , bringing your own shopping bag

A: The manufacture of them certainly takes some energy. The manufacture of anything takes energy. The composting doesn’t really use much especially if is in a home compost heap as its your own human energy in heaping it up, adding things to it etc. The wrapping on a cucumber is polyethylene I think and this is not a biopolymer.

Q: What are your thoughts on items which claim to be compostable as they will break down to less than 10% of their orginal size within a given time frame therefore meeting a certain composting standard, but the leftover material can be nano layers of film or metals which I don't feel should be called compostable.

A: Yes, wrapping that is a mixture of components are a bit problematic. It would be good to have all biodegradable components in such wrappings.

Q: Considering the widespread confusion and misappropriation of the word 'Biodegradable' to date (note EU ban on popular Oxo degradable polymer additives), is there a justification for not using the word at all when discussing plastic intended to break down fully in a natural/composting environment?

A: Yes, the words we use are sometimes problematic and defining these better would be useful for the public. The introduction of oxo-plastics is a bad move. These should not be allowed.

Q: Most people don't compost. Do we know what the national state of play is with industrial composters? How many authorities are using them? Are any? And is there data from their use?

A: 50% of councils in England offer a food waste collection service, which will be taken to industrial composters.

Q: The degradable films seem to act like leaves and stick together blocking out the air. This seems to be why this is still remaining rather than a chemical issue.

A: Mixing things up just before putting into the compost heap and mixing with some shredded paper or cardboard helps to introduce some spaces and air pockets.

Q: Can oil based plastics be broken down by bacteria or fungi?

A: This is only possible at the moment for PET water bottles and this is has only been developed in the last year by a French company. Its not yet possible for any other plastic made from oil. We are currently researching at UCL the breakdown of nylon, Lycra and polyurethanes by bacteria and their enzymes. Its all at the research stage and a long way from any big process.

Q: Are UCL working with Bangor University and TUV Austria? I think TUV have a home composting mark...

A: Not directly with Bangor or TUV Austria. We are working with REAL on UK compostable certification

Q: In Portland, Oregon, they ban compostable plastics in yard & food waste collection. The idea is that they don't contribute nutrients to compost. Probably also people accidentally put in non compostable plastics because they can't tell the difference.

A: Proper bioplastics such as PHBs and PLAs DO contribute to the soil, compost and biomass.

Q: When will all local councils adopt the same recycling systems?
A: The Environment Bill, which is currently before Parliament, stipulates a consistent set of materials that must generally be collected from all households and businesses for recycling, including food waste. Councils would have to provide this service by 2023.

Q: What do you think will be the most important thing to improve the understanding of these issues within government? e.g. the problems with labelling vs infrastructure

A: All of the issues are interconnected, which is why we will be taking a whole system view in the next phase of our research. E.g. the type of infrastructure that is available will affect what the label needs to say.