There is nothing wrong with composting of garden and kitchen waste, but no
plastics of any kind should be introduced into the process.

A “Grocer” magazine survey of more than 1,000 individuals in 2019 found that
“consumers think that plant-based compostable plastics are the most
environmentally friendly packaging materials,”

but most consumers don’t realise that “compostable” plastic
does not convert into compost.  It is required by ASTM D6400
and EN13432 (and clause 6.3.2 of the draft Kenya Specification)
to convert rapidly into CO2 gas, and the last thing the planet
needs is more CO2

Also, many consumers do not know that “compostable” plastic is tested to
biodegrade in an industrial composting facility – not in the open environment.
In November 2019 a Danish court ruled in Ellepot v Sungrow that “compostable”
PLA plant pots must not be described as biodegradable – because they are not
biodegradable except in the special conditions found in an industrial composting

“Compostable” plastics are really an irrelevance, because the main problem facing
governments today is plastic waste which has escaped into the open environment,
from which it cannot realistically be collected and taken to a composting facility.

Plastics marketed as compostable (ie hydro-biodegradable plastics)
are far too expensive for everyday use, and there are very few
industrial composting facilities available. For this reason the
German courts in Güthoff v Deutsche Umwelthilfe (2014) held
that it is deceptive to market plastic as “compostable.”

These plastics are often marketed as renewable, but this ignores the fossil fuels
used in the agricultural production process by the machines which clear the land,
plough the land, bring the seeds to the farm and sow them, harrow the land, bring
the fertilisers and pesticides to the farm and spread them,  harvest the crop and
transport it to the factory, and by the machines which polymerise the raw material.

It also ignores the land and water resources devoted to producing the raw materials,
which could be used for growing food. EASAC (March 2020 report) says that
“replacing PE by a bio-PE would require almost all (93.5%) of global wheat production.”
This is completely unsustainable.

Although these plastics are marketed as “bio-based” they can contain up to 60%
oil-based material, but this is hardly ever mentioned in the marketing material.
Conversion of organic materials to CO2 at a rapid rate is not ”recovery.” Nature’s
lignocellulosic wastes do not behave in this way, and if they did the products would
have little value as soil improvers and fertilisers, having lost most of their substance
and their carbon.

On 11th September 2003 a Report to the Australian Government by the Nolan-ITU
Consultancy concluded that: “oxo-biodegradable plastics based on polyolefins
contribute to the amount and nutritive value of the compost because much of the
carbon from the plastic is in the form of intermediate oxidation products, humic
material and cell biomass.This is in contrast to plastics such as hydro-biodegradable
polyesters (eg starch-based) that biodegrade at rates comparable to purified cellulose.
At the end of the commercial composting process, all of the carbon from the latter
has been converted to CO2 so there is a contribution to greenhouse gas levels but
not to the value of the compost.”

The same Report concluded that “degradable polymers manufactured from
renewable resources (e.g., crops) have greater impacts upon eutrophication due to
the application of fertilizers to land.”

On 15th July 2020 a report appeared in “Waste Management” Vol. 113, Pages 312-318.
The conclusions were:

  • In many cases, plastic bags are being replaced with compostable plastic bags.
  • Industrial composting processes do not completely remove film fragments.
  • Compost is thus a potential source of fragments from compostable plastic bags.
  • Compostable plastic fragments are then deteriorated in soil to microplastics.
  • Compostable microplastic results in an increase number of aflatoxigenic fungi.


Composters reject it

Even industrial composters and local authorities do not want ”compostable”

For example, Epsom & Ewell Borough Council in the UK link  Their website
says “When you use plastic bags in your food waste caddy you’re simply
using them to contain the food, and keep your caddy clean. They don’t get
recycled. In fact, the first thing that happens when your food waste gets to the
recycling plant is the plastic bags are all dredged out. They’re sent off for
burning along with normal refuse to generate electricity. After that, the food
waste can be recycled.”

“We used to ask you to use bio-liners to line your food waste caddy, but the
food waste recycling companies found that bio-liners compost down much
more slowly than the food. That slowed the recycling process and made it
much more expensive. They tried dredging the bio-liners out of the food waste,
but the sticky bio-liners got tangled around the dredging equipment.Cleaning
them off was very expensive. So they found that using plastic bags was,
overall, much more cost-effective.They’re not recycled but good stuff still
happens to them. And you can use old bags like bread-bags or carrier
bags if you like.”

  • The City of Exeter UK has also rejected itClick to read 
  • And the City of Toronto, Canada Click to read
  • In January 2020, the industrial composters of Oregon gave 9 reasons
    why they did not want it Click to read it
  • Then the SUEZ  waste-management companyClick to read
  • Then a devastating exposé on Netherlands television Click to read
  • And another TV exposé in Canada about how compostable plastics
    are typically not being composted but instead sent to landfill
    or incineration.Click to read 

Many areas do not have industrial composting plants, and the Welsh Government
has refused to invest in them. – Click to read  Plant-based compostable plastics are
going to landfill rather than recycling because so many local authorities are unable
to deal with them.

“Compostable” resins are worse than conventional or oxo-biodegradable plastics
when it comes to oxygen transmission-rate or moisture vapour transmission-rate.
These resins are also water sensitive, and their physical, optical, mechanical, and
chemical properties are inferior.

There are at least 21 reasons why “Compostable” plastic is not useful
Click to read in English/ Click to read in Spanish


Why would anyone want to buy an expensive plastic bag to transport kitchen
waste to a home compost when he could use a bucket?  The very idea
is a nonsense.

Home composting of plastic is in any event dangerous and should not
be encouraged:

A study for the French government at link says that “composting management
must be in line with good practices recommended by ADEME (weekly brews
for one month and then every 1 to 2 months, humidity control), – the average
ambient temperature over the first three months of composting must be close
to that of the standard: outside temperature of 25oC – 5oC. It is unlikely that
all of these conditions will be met by individuals.”

The study also shows that “plastic bags are poorly disintegrated
and biodegraded if good domestic composting practices
are not applied. It also shows that, even when good practices
are followed, there are still a few pieces of plastic bags of
micrometric or even millimetre size in composts beyond the
standard year of home composting.”

In addition, the study says “it appears that the biodegradation of plastic bags
suitable for domestic composting makes little or no contribution to the formation
of humus because, in accordance with the biodegradation tests of these materials
according to the NF T 51-800 standard, at least 90% of the carbon organic dioxide
is converted into carbon dioxide.”

Worse still, there is a danger that the plastic may have been
contaminated by pathogens eg from putrifying food, and that
the temperature in a home compost may not be high enough
to kill those pathogens.