Most PLA plastic is marketed as compostable. However, when you read the fine print, most compostable PLA (polylactic acid) requires industrial facilities to break down. We have successfully been composting small amounts of PLA in our Pilot Compost Project using aerated static piles, but we also want to know what a typical home tumbler can handle.
Not all PLA is compostable, or even biodegradable. However, PLA meeting EN 13432 should compost in ideal conditions (ie commercial composting) without leaving behind and residues which can be toxic to the soil. PLA with the TUV OK HOME Compost (Formerly vincotte) should compost in the conditions found in the typical home pile.
PLA melts at 320 degrees Fahrenheit, but begins to degrade much lower. Temperatures between 111 and 140 degrees Fahrenheit cause PLA to warp and hasten the process of breaking down. EN 13432 tests use 136.4 degrees Fahrenheit. ASTM D6400 uses temperatures above 122 degrees Fahrenheit.
PLA is considered a brown, with a similar C:N ratio to that of paper. However, we prefer to keep PLA inputs low enough to not effect the overall C:N ratio. There is a studying showing PLA can make up to 30% of a pile without causing any negative effects.
Tumblers (or Home Piles) VS Commercial Piles
The main difference between home piles and commercial piles is temperature. The volume (under 1m3) and method of creating a home pile makes reaching and maintaining thermophilic stage composting difficult.
Our home tumbler consistently reaches temperatures between 110 and 120 degrees Fahrenheit when well fed and well managed, with some peeks to 130. However, because of the small volume, these temperatures are only maintained if the compost is constantly fed. Balancing greens, browns, and moisture in a tumbler can take some practice, but the faster compost production (and lower odor) is worth the effort!
An average tumbler only holds about 15-20 liters per batch. A 33 gallon DIY trash can composter can be easier to manage, as the larger volume (125 liters) can get hotter, and stay hot for longer.
The home pile temperature is lower than the EN 13432 or ASTM D6400 test temperatures, so compostable PLA in a home pile or tumbler is unlikely to complete the process of biodegradation within the time limits.
On the other hand, our aerated pile (1m3 / 1,000 liters) maintains a temperature between 130 and 140 degrees Fahrenheit for weeks at a time, and peaks to 160! The microbes responsible for thermophilic composting thrive between 105 and 140 degrees. They begin to die off at temperatures above 160 degrees Fahrenheit.
Because of the risk of microbe die-off, industrial piles are often turned, aerated, or otherwise cooled when they begin getting too hot. Still, large compost piles have no trouble maintaining the temperature required to break down PLA that has passed EN 13432.
As expected – compostable PLA quickly becomes undetectable in our Aerated Pile – breaking down much faster than wooden cutlery or toothbrushes, which are always still visible on the first turn. You can see our current compostability tests here.
Actual Home Compost Tests
Science and certification aside – what actually happens when you put PLA in a tumbler? Some items break down faster than we expected, but don’t expect miracles unless your tumbler is large and HOT.
Given enough heat, PLA starts to break down almost immediately by clouding over, shrinking, distorting, and becoming brittle. You can also clearly see moving masses of microbes feasting on the PLA the same way they do on vegetable matter.
When the rest of the compost was almost finished, a small section of straw and the base of the cup remain large enough to spot easily. We usually sift the finished compost and throw PLA (and plenty of other large organic undigested pieces) back into the tumbler to go through the process again. Eventually everything breaks down into homogeneous compost. It just takes much longer than the 12 weeks as prescribed by the EN 13432 or ASTM D6400 standards.
Neither product is marketed as suitable for home composting, and as such we don’t recommend you compost PLA at home. However, if you are working towards zero waste, an occasional PLA product does seem manageable in a hot home compost.
Remember, in a landfill conditions are designed to be anerobic (without oxygen). Compostable bio-plastics are NOT designed to be broken down in landfill conditions.
In the USA, compost produced with feed-stock containing PLA can not be certified for organic agriculture.
Some More Information:
The straw and the cup are made of different types of PLA. The straw says ‘I’m compostable’ on the wrapper, but does not list any further information on the box.
The cup is from greenware and is widely available on SXM, including at PDG Restaurant Supplies. The greenware website lists the standards (ASTM 6400) they adhere to, and seems to take their anti-greenwashing pledge seriously.
However, to make compostable PLA fulfill all its green promises, the infrastructure needs to be in place for industrial composting. Otherwise, it is still likely to end up in the landfill, or worse, in our ocean.
For comparison, a PLA cup used as a seed starter is only just starting to show signs of wear six months later. Under landfil conditions, PLA might be around for a lifetime. In the ocean, PLA will certainly be around long enough to endanger marine life while causing an unsightly mess.
PLA has improved greatly since its first introduction. It’s production does have a slightly smaller carbon footprint compared to petroleum based plastics. However, the industry has a long way to go.
Remember, we should always strive to use reusable products instead of single use items!
There is no ‘away’. Anything we dispose of must end up somewhere, be it the landfill, incinerator, recycling plant, or as compost. Choose wisely!
Remind servers that you won’t be needing a straw, and take a to-go cup with you!
This post contains affiliate links through amazon.com and we may be compensated (at no cost to you) should you decide to buy online using one of our links. However, for our St Maarten / St Martin visitors we encourage you to shop local, and every effort has been made to provide a local source. Please let us know if you want to be included!
Sources:
http://compost.css.cornell.edu/physics.html
https://www.creativemechanisms.com/blog/learn-about-polylactic-acid-pla-prototypes
http://www.bpf.co.uk/topics/standards_for_compostability.aspx
https://mcgillcompost.com/biodegradable-plastic-compostable-plastic
Hello! Our restaurant recently switched from plastuc straws to PLA. But it is my understanding that unless the PLA’s are composted properly they are still harmful to the environment. I have been scouring the web for information on where or how to compost them. I would be unable to handle the volume of straws i think if I had a home-composting set up, but I don’t yet. Can you please help me? I’ve sent already 6 emails to different places in the last 3 weeks with no reply, to other eco-conscious organizations and to local composting facilities. Thank you so much!
That is a really difficult question! The best will always be ditching single use entirely. Paper is probably better than PLA when used outdoors or at the beach (but doesn’t work so well for frozen cocktails!). The production of PLA does have a smaller carbon footprint compared to conventional plastics, but the actual reduction varies by source. It is reported to not leach harmful chemicals (BPA and the like).
Switching to PLA also shows that there is demand for an alternative to plastic, so hopefully that encourages more research and the development of home compostable options.
As for handling a restaurant’s worth of straws at home, yes, that would be extremely difficult. Depending on the size of the restaurant, there are in-vessel composters designed to handle restaurant waste and some of them are currently used for PLA service-ware, table scraps, and prep scraps.
There is a growing trend in residential compost pick-up services, and many of them are working with compost facilities that handle PLA service-ware. Hopefully you can find one local to you!
Ηοw about using the tube pasta used in Greek pastitsio. These work great as straws and can be composted with other food waste from the restaurant.
Hi There,
Firstly, great article! I do have a question on PLA. I sell compostable phone cases. They contain just a few percent of PLA (mixed with PBAT and bamboo fibre), and I tell my customers that they need to be composted at 60°C (140° F), or sent to me for commercial composting. A compostable mailer company then told me that their mailer containing PLA can be home-composted below the temperature… They are also certified to be compliant with home composting standards. This contradicts articles, such as yours, that I have read about PLA stating that it can only compost in hot compost.
Are we able to compost PLA in a home compost, where the temperature does not reach 111°F – maybe it would just take longer (e.g. 2-3 years)? Or is PLA not home-compostable at all unless it is in a hot compost?
I’d really really appreciate a reply as it is quite difficult looking for answers online regarding this!!
Thanks,
Lily
Yes and No :p
Some PLA (especially in Europe) is certified as home compostable. It is usually a thin film which is slightly (or completely) opaque and has a different texture compared to regular PLA, or it is more like a traditional cellophane product. Both have a poor shelf life compared to regular PLA and petroleum based plastic.
TUV Austria has TWO certification standards, Industrial and HOME. So far we have only seen Industrial out of the USA. “TUV Austria HOME” composts fine in our test tumbler and our test piles (and is probably what your mailer company is talking about). However, I have spoken to many people who are unsuccessful even with TUV Austria HOME compostable PLA. Unfortunately compost piles vary greatly!
Part of the TUV certification is to ensure that any remaining particles are not toxic or harmful. While one may be comfortable pulling PLA pieces out of finished compost and adding them back to the pile, not everyone will have the same views.
Hi:
Where can I get one of those 1,000 gallon composting bin that you mentioned that will get up to 130 +F ???
We made our own 3 bay aerated compost (More info here: https://greensxm.com/aerated-compost/).
There are a number of commercial systems available. We haven’t tried out any, but use the search term ‘In Vessel Composting’ to find what is available in your area. We found Tidy Planet (based in the UK) to have a very nice containerized system.
I’d like to point out that recycling PLA is also an option. The problem, similar to composting, is that it requires dedicated PLA collection since it will degrade the quality of petroleum based plastics like PET and PP. so you won’t be able to put them in a normal recycling bin.
That is a good point! Unfortunately not available where we are based, but hopefully end of life options for PLA will increase. (And as always, reusable still wins overall!)