Biodegradable versus compostable – knowing your eco-plastics
IT’S not uncommon nowadays to receive a takeaway coffee in a biodegradable plastic cup or to get a burger from a food-truck in a compostable plastic container. Many shelf products now use biodegradable plastic packaging as well. The global demand for biodegradable plastics in 2018 was 360,000 metric tons according to analysis by IHS Markit, but it is expected to increase to nearly 550,000 metric tons by 2023.
CSIRO environmental chemist Dr Mike Williams says the change is happening through bottom-up processes.
“The shift is largely due to consumer awareness of plastic waste driving a preference for greener alternatives,” says Williams.
Governments and regulating bodies are also creating this shift. This year, the European Union moved to ban a range of single-use plastics such as straws and food containers. In Australia, cities and local governments are following suit, and the two biggest supermarkets have banned single-use plastic bags. Environmental ministers in Australia have also endorsed a target of 100 per cent of Australian packaging being recyclable, compostable or reusable by 2025.
Not always bio, not always degradable
Biodegradable plastics encompass a broad range of plastics made from different materials but are defined by their ability to break down completely into natural substances, according to the Australasian Bioplastics Association. They state that biodegradable plastics are either biobased, made from plants such as corn or sugarcane, or made from petrochemicals. Confusingly, the term “bioplastics” can be sometimes used to mean biodegradable or biobased plastics, or both.
Products labelled as biodegradable plastics are sometimes actually made from oxo-degradable plastics. Williams says this is misleading and bodies such as the Australian Competition and Consumer Commission are working to combat this as it is an environmental concern.
“This type of plastic has a metal added to it so when it’s exposed to light or heat it breaks down. Which seems good, but it doesn’t really break down, it just breaks down into smaller pieces which we call microplastics,” he says.
“Microplastics are a serious environmental issue as they are more challenging to clean up, and move more easily through the environment to affect organisms.”
The cycle of carbon
The majority of biodegradable plastics on the market are compostable plastics. Most of these will only break down in industrial composting facilities, with some also breaking down in home compost.
“Compostable plastics are a very specific definition of plastics,” says Williams.
“According to Australian standards, a compostable plastic must degrade within a certain time period in a composting facility. If the context of disposal is not right, then it won’t break down very well. Plastic compostable forks are made of a thicker plastic, so if you put them in landfill they’d probably be there in 50 or a hundred years’ time just like a normal plastic.”
Infographic: New Zealand’s Parliamentary Commissioner for the Environment, CC BY-SA.
Show descriptionHide descriptionWilliams says compostable plastics break down into natural substances.
“Basically, the carbon is converted into carbon dioxide and carbon that microorganisms can use for their metabolism. This is the basic premise for biodegradation and, in theory, everything containing carbon can be biodegraded. However, the carbon in conventional, and oxo-degradable, plastic takes considerably longer to biodegrade. This is because microorganisms have trouble accessing this pool of carbon due to its structure in the plastic.
“So, the compostable plastics are essentially converted into compost and CO2, which could be used to improve soils for more efficient and sustainable production of crops, such as corn. It can be even used to make more compostable plastic, although this may not be the best use of food crops.”
Waste not, want not
There is a risk that consumers might misunderstand how to dispose of compostable plastics. Williams says this is a problem if they are disposed of in the wrong circumstances.
“If they break down in a landfill where you have low to no oxygen, then you get production of methane, which is a powerful greenhouse gas,” he explains.
Williams and his team are working with the New South Wales Environmental Protection Agency to investigate the use of compostable plastics on a larger scale, to anticipate a likely increased use and, therefore, disposal in composting facilities.
Image: CSIRO / Mike Williams
Show descriptionHide descriptionHe says that composting facilities are very efficient at breaking compostable plastics down.
“Compared with home composting, an industrial composting facility operates at around 60 °C or above – when you have those high temperatures along with moisture and oxygen, compostable plastics disappear quite quickly. We hope to show a large increase of compostable products entering industrial facilities will not impact on the operation of the facility or the finished compost product.”
November 7, 2019 at 4:17 pm
Hi, I’m Nicho from student in Semarang, Indonesian. The part of increasing consume plastic in the world by people. I have an good idea by applying paid plastics and the price is very expensive, with this idea it is expected that people bring their respective shopping bags and of course environmental friendly.(3/25)
December 2, 2019 at 1:02 pm
Hi Bang,
Thank you for your email as well. This response is from Dr Mike Williams (Research Scientist at CSIRO).
“Thank you for taking a strong interest in environmental issues and trying to understand how you can contribute to solving these problems – it gives me a lot of encouragement in my own career to think young people are engaged with such important topics! I have recently been in talks with Kopernik (https://kopernik.info/), an NGO based in Bali, as they have been wanting to understand whether replacing conventional plastics with compostable/biodegradable plastics can help in reducing ocean litter. They may have a better understanding of potential programs that could be implemented in schools. I also agree that price is one of the major factors related to plastic litter; plastic is very cheap and only when it has more value, will we value it more (and not dispose of it so thoughtlessly).”
November 11, 2019 at 8:23 pm
Hello the writer
I am a student from SMA 11 Semarang in Indonesia. in my school there is a movement to reduce disposable plastic waste but there is no alternative way to overcome the problem. I have read your article and I already know about your program, I want in my school to make a program like that. I want to ask how tips for realizing the program? (Fahrul XII MIPA 3/ 14)
November 19, 2019 at 10:53 am
Hallo writer
I’m student in eleven senior high school in indonesia
I was read your articles
Your articles very interest
I want to make your program in my school
So i want to ask you
What is step to make the program? I hope you answer my question ( XII MIPA 3/ 14
December 2, 2019 at 1:02 pm
Hi Fahrul,
Thank you for your email. This response is from Dr Mike Williams (Research Scientist at CSIRO).
“Thank you for taking a strong interest in environmental issues and trying to understand how you can contribute to solving these problems – it gives me a lot of encouragement in my own career to think young people are engaged with such important topics! I have recently been in talks with Kopernik (https://kopernik.info/), an NGO based in Bali, as they have been wanting to understand whether replacing conventional plastics with compostable/biodegradable plastics can help in reducing ocean litter. They may have a better understanding of potential programs that could be implemented in schools. I also agree that price is one of the major factors related to plastic litter; plastic is very cheap and only when it has more value, will we value it more (and not dispose of it so thoughtlessly).”
February 20, 2020 at 12:47 pm
There’s so much information online about plastics. Even after reading this article I’m confused. May I just ask, what is the better choice for our environment: Biodegradable or compostable plastics?
Thank you so much!
March 24, 2020 at 3:32 pm
Hi Emma,
Here is a response from CSIRO environmental chemist Dr Mike Williams.
“Thanks for your interest in helping to reduce the environmental impacts of plastics. The short answer to the question is a favourite one used by scientists – it depends!
As the article states, everything is theoretically biodegradable and even conventional plastics will be biodegradable although it may take decades to centuries. Compostable plastic is a specific definition that states under certain conditions (usually elevated temperatures and moisture), plastic must biodegrade into its basic elements (e.g. carbon dioxide) within a particular timeframe (usually months).
Most compostable plastics need to be biodegraded in commercial composting facilities which can operate at high temperatures and moisture levels. Some compostable plastics are home compostable which means they can biodegrade at lower temperatures like those found in home compost heaps. However, they still do need reasonably high microorganism loads and consistent moisture levels, otherwise they are likely to behave like conventional plastic i.e. taking years to decades to degrade. Therefore, if these plastics are not disposed of appropriately (e.g. in a commercial green-lidded bin) they can behave like any other plastic in the environment. Not good!
Also, compostable plastics can be produced from either oil or plant material. The energy required to produce and transport them, the terrestrial footprint of the raw material, the economic cost of using them and the appropriate collection and treatment of the plastic after its use all need to taken into account when thinking about the environmental impacts of plastics. Sometimes biodegradable plastics may have an overall environmental impact similar to conventional plastic if care is not taken at each of the steps from production, use and disposal.
Apologies if that did not reduce your confusion! If you reduce your overall use of plastics in day to day life, ensure plastics are placed in the correct bins (check the recycling codes on the product) and, yes, use compostable plastics as an alternative to conventional plastic where available, then you are taking a positive step towards reducing environmental impacts of plastic. Remember, compostable plastics are clearly marked in Australia as AS 4736 (suitable for composting in a commercial facility) or AS 5810 (suitable for home composting) and sometimes with a recycling code “7”.”
Thanks!
May 20, 2020 at 2:45 pm
Hello Kate,
Great response, one other question – are compostable plastics suitable for the recycling stream? I have heard that there is too much plant based material and not enough plastic material and they simply float to the top when processing.
For a product to be properly reprocessed, it needs to end up in the correct place – compost facility or recycling facility
May 27, 2020 at 2:30 pm
Hi Emma,
Another great question! This is Dr Mike Williams’ response.
Generally the answer is “no” but this is more related to the ability (and economics) of recycling facilities to handle this waste than the inherent recyclability of the product. If they are labelled “compostable” to the relevant Australian standards, best to pop them in a green bin (if your council has this facility) or out by the chook shed!
Thanks!
CSIRO
March 25, 2020 at 11:16 am
Wow! What a thorough & very much appreciated reply. Thank you so much!
August 27, 2020 at 11:51 pm
Hello! I was wondering if there had been any research into the effect that compostable plastic has on compost. Is it still as “good” as compost made from normal organic waste?
I also read a quote from Mike in an article on Renew about industrial facilities taking 2-3 months to process their waste. With the Australian standard, compostable plastics may have 10% of material left after 180 days. Is this still the case? Do the industrial facilities then deem the final compost to be contaminated and chuck out the whole lot?
Thank you!
September 6, 2020 at 8:47 pm
Hi, I would like to know if there is 100% bio degradable plastic available in the market.
Your response would be much appreciated.
March 25, 2021 at 1:01 pm
Its a crying shame that compostable plastics end up in compost as end of life if we consider all the energy and resource that went into producing biopolymer (agricultural land/energy to grow the sugars to feed the bacteria for poly lactic acid). Also the extraction of lactic acid from the fermentation broth, followed by the polymerisation to poly lactic acid is energy intensive, and some of the chemicals are well, bad for the environment. That’s why we have been working on coupling two stage anaerobic digestion of food waste, by extracting the lactic acid out of the first stage acid fermentation – please read here: Bühlmann, C. H., Mickan, B. S., Tait, S., Renton, M., & Bahri, P. A. (2021). Lactic acid from mixed food wastes at a commercial biogas facility: Effect of feedstock and process conditions. Journal of Cleaner Production, 284, 125243.