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Plastic in my compost
| News| 27/02/2018

Ignasi Puig Ventosa | ENT

We have been composting for many years at home. We only put leaves from the garden and pruning waste, nothing from the kitchen. It is something like two or three cubic metres. A couple of times a year I take around 100-150 litres of compost from the bottom.

For a long time, I have been disturbed to see that in any handful of compost I take from the pile I can find some plastic, visible, without exception. Sometimes it can be a piece of a broken clothes peg or a bristle from a broom, but most times they are pieces of discarded bags or other light elements which arrived in the garden flying from outside or which have slipped under the garden gate, and which ended up in the pile after having been swept up inadvertently.

In just a few decades plastics have become omnipresent in our society. But, unfortunately, the consequences of their use last far beyond their useful lifetime. Everyone is aware of their overwhelming dispersion in our landscapes. The situation in the oceans is not better [1]. As a reaction, a few thoughts spring to my mind.

First of all, it is clear that the industry is assuming very little responsibility, and that Public Administrations are complicit with this. Extended producer responsibility only affects –and only partially– those plastics used as light packaging, in vehicles, in tyres or as part of electric and electronic equipment, not any of the others. Also, recycling levels are not sufficiently high, as a result of poor separate collection systems and inefficient treatment facilities. As a consequence, society has to face not only the problems created by those materials which are not recycled, but also has to assume a high share of the costs of managing them as waste.

Secondly, it illustrates the importance of the quality of the materials that we aim to recycle, and thus the importance of separate collection; for all materials, but particularly for biowaste. Although most composting and anaerobic digestion facilities have the capacity to separate some of the impurities (of which around 40% can be plastics), this separation is far from perfect. Two recent studies confirm that the quality of compost is influenced by the presence of impurities in biowaste [2] and that, in turn, the presence of impurities is influenced by several factors [3], among which particularly the type of separate collection scheme, door to door separate collection models being those presenting better results.

Thirdly, it makes clear the urgency to adopt measures that address the root of the problem. High quality separate collection and sound waste treatment are necessary, and allow enormous room for improvement, but they are end-of-pipe solutions. It is also important to promote greener consumption patterns through environmental awareness campaigns, but this is not enough either. We have to address the problem where it is created. And this requires measures of higher impact, such as taxes on certain products (e.g. disposable ones) or on certain materials, compulsory consideration of eco-design criteria, generalisation of the extended producer responsibility or –why not?– prohibition of certain plastics (e.g. oxo-degradable ones) or of certain uses (e.g. microplastic beads in cosmetics). One can think that these measures are a bit too hard, but honestly, after wandering around beaches and mountains, and finding plastics absolutely everywhere, I am bit disappointed with the outcome of soft solutions.

On 16th January 2018 the European Strategy for Plastics in a Circular Economy was adopted [4]. A number of measures will need to be applied by the European Union (listed in Annex I of the Strategy), by Member States and by the industry (Annex II), but also by Regional Governments and Local Authorities. No doubt that implementing the Strategy will bring about significant advances, but only time will say if it is sufficient to address the huge challenge we face.


[1] See for example:

[2] Campos Rodrigues, L., Puig Ventosa, I., López, M., Martínez, X. (2016) Anàlisi de la incidència dels impropis de la FORM sobre la qualitat del compost de les plantes de compostatge de Catalunya

[3] Puig-Ventosa, I., Freire-González, J., Jofra-Sora, M. (2013) Determining factors for the presence of impurities in selectively collected biowaste, Waste Managament and Research, 31: 510-517.

[4] The strategy and several accompanying documents can be found in this portal: