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The Big Compost Experiment

When a cup manufacturer says their cup is ‘compostable’, what does this actually mean? Can it be composted at home? Does the council compost it?

These questions have bugged and preoccupied me for the last few years since I set up Plastic Free Faversham and have been advocating for a reduction of waste and single use plastic in our community.

Two examples of compostable plastic given to me by Faversham takeaways. Both made from PLA (Polylactic acid – Made from plant starch), both claiming to be ‘compostable’ (though no clarification given as to whether this means commercially compostable or home compostable).

Compostable plastics, though still single use and therefore still essentially profligate with the earth’s resources, have two claims to being ‘greener’ than conventional plastics:

  1. They are made from plants (which are renewable) as opposed to fossil fuels (which are not) – e.g. corn starch, sugar cane, cellulose

  2. They can be recycled back into organic matter and this compost/soil conditioner can be sold for use in agriculture

The trouble is that No 2 there is EXTREMELY misleading. They are technically compostable, but only in very specific conditions that the general public have no access to. Very few councils in the UK have systems in place to collect compostable plastics and compost them, so the only place to dispose of them is in the general waste bin which goes to landfill or incineration. I don’t know if other countries are better on this – I’d be interested to find out.

How about composting these things at home in your own compost bin? Well, most compostable plastics can only be broken down in industrial facilities that reach very high temperatures. The cup in the picture top left, for example, says ‘Compost me’, but if you look at the brand’s website this cup is there described as ‘commercially compostable where accepted’, so the chances of this cup actually being composted are slim to nothing.

However, there are some compostable plastics that claim to be, or are certified to be, suitable for putting in your home compost bin. And this is where the Big Compost Experiment comes in.

The Big Compost Experiment is a citizen science research project led by UCL’s Plastic Waste Innovation Hub. Its aim is to find out whether home compostable plastics really do work in practice – and the only way to do that is to ask the UK’s community of home composters to try it out. And now that I’m a compost geek as well as a plastic geek I reckoned I should get stuck in and involved!

How does the Big Compost Experiment work?

There are two parts that you can get involved in – both dead easy. Firstly, a short online survey (link here) that everyone can do, whether or not you compost at home. It asks you about your views around compostables/biodegradables as well as how you would dispose of them, and whether you home compost.

The second part is the fun bit if you compost at home because it involves taking part in a mass practical experiment. You simply take one or more pieces of compostable plastic (i.e. marked clearly as ‘compostable’ or ‘home compostable’), upload a few photos of them, answer a few questions about how you compost and off you go – pop the item in the bin until you get a reminder 6 or 12 months later to have a look at how well (or not) they’ve composted.

So I selected a few compostable plastics I’d been given by local cafes and into my compost bin they went. Two were marked simply ‘compostable’ without any clarification about whether home compostable or commercially compostable – these are the two I have officially entered into the experiment. The third is marked ‘commercially compostable’ so presumably will not break down at all, and the fourth, a paper cup with plant-based plastic lining is simply labelled ‘biodegradable’ (I’m expecting that this thin lining will be the first of the plastics to disappear).


My last lot of compost took about a year to fully mature so I am aiming to report back to the UCL project them – and will do a blog post to let you know!

This document, just published by UCL, gives an excellent overview of the research findings so far. It’s very digestible – I really recommend you have a look.

My compost bin -a Green Johanna

In case you’re wondering, my compost bin is called a Green Johanna. I got it as it came highly recommended by the Eco-Cops, a Facebook group of eco brain-boxes I follow, and was also heavily subsidised by Swale council (reduced from £120 to £73). It’s pricier than the average plastic bin like this because the design makes it suitable to putting in all food waste, including dairy, meat and fish which are usually compost no-no’s. You can get more information here, and see if your local council also gives the subsidy.

#bigcompostexperiment #plasticwastehub #Composting #biodegradable #compostablepackaging #plasticfreefaversham

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