2023-03-22 08:49:08
This article is republished from The Conversation under a Creative Commons license. Read the original article.
These practices are expected to develop more and more: from December 31, 2023, it will in fact be prohibited to throw bio-waste into the traditional trash can. In accordance with the law of February 10, 2020 relating to the fight once morest waste and the circular economy, they must be sorted at source in order to be recovered.
By way of derogation, the decree of March 15, 2022 will authorize the joint collection of certain compostable, methanizable and biodegradable packaging and waste with this biowaste. It will then be possible to eliminate bags made of paper, cardboard or plastic materials called “compostable in domestic composting”.
“Compostable plastic materials”
The latter are, like all other plastic materials, mixtures composed of polymers and additives. The constituents of these mixtures generally originate from chemical substances derived from petroleum, but they can also come from biomass, with a plant (e.g.: cellulose from wood) or animal (e.g.: casein from milk) origin. ).
Certain plastics aspire to be bio-based plastics, even if they are only partly made from biomass resources. Today, the minimum content of bio-sourced materials (50% since January 1, 2020) is only regulated for single-use plastic products.
For other applications, no regulatory threshold is imposed in the event of a “biosourced” claim.
Criteria defined by two standards
So-called compostable plastic materials must meet two criteria: be biodegradable, that is to say be decomposed naturally by biological organisms (micro-organisms, etc.) and degrade under specific, well-defined laboratory conditions (temperature, duration of the process, humidity, etc.).
Depending on those applied (such as the temperature and duration of the test), we then speak of either industrial composting (40-50 °C, 6 months) or domestic composting (25 °C, 12 months).
All of these conditions are defined in two standards: the European standard NF EN 13432:2000 for the industrial composting of packaging and the NF T51-800:2015 standard for the domestic composting of plastic materials.
Plastics and domestic compost
To meet the compostability requirements in a domestic environment described in standard NF T51-800:2015, plastic materials labeled “domestic compost” must meet the following criteria:
The material to be tested must not contain substances of concern for human health and the environment such as CMR substances (carcinogenic, mutagenic or toxic for reproduction), endocrine disruptors, etc.
Under the effect of composting, at a temperature below 30°C, the material must break up into small pieces. At the end of 12 weeks of testing, only 10% of the initial mass of the material must have a size greater than 2 mm. Disintegration residues in the compost must be indistinguishable to the naked eye (distance of 0.5 m).
Within 12 months, at least 90% of the material’s constituents must biodegrade to produce water, carbon dioxide and microbial biomass. No negative impact on the quality of the compost should be observed following the compostability test.
Tests not very applicable in domestic compost
The test conditions presented in standard NF T51-800:2015 are not easily transposable to a domestic composter. There cannot, for example, be a constant test temperature of 25°C for 12 months.
The T51-800:2015 standard further specifies that the tests must take place with only 1% by mass of plastic materials while individuals will continue to feed their composters with bio-waste (and therefore possibly with compostable plastic materials). It is therefore impossible to guarantee that all so-called compostable materials will degrade within one year if this rate recommended by the NF T51-800 standard is exceeded.
Under these test conditions, the minimum biodegradation rate to be respected is 90% following a 12-month test period. However, no additional study is required on the remaining 10% of the constituents which have not deteriorated. Therefore, if some of them are dangerous for humans and the environment, they risk being spread in the domestic garden and in fine contaminate cultivated foods.
Domestic vs. industrial composting
Ademe also demonstrated in a study that the disintegration rate of certain bags made of so-called compostable plastic materials was lower than that recommended in the NF T51-800 standard, due to insufficient mixing of the contents of the composter by users. Fractions larger than 2 mm then remained.
The domestic composting process is less efficient than industrial composting since the test temperature is lower (25°C compared to approximately 55°C). It does not apply to all so-called compostable plastic materials because some do not degrade in a domestic composter. They must therefore first be collected by professionals so that they can be sent to industrial composters and recovered.
As it is not legally possible to check in private homes whether the materials and users comply with all the requirements contained in the domestic composting standard, ANSES encourages public authorities to prohibit the introduction of plastic materials (compostable or not) in domestic composters, contamination of the environment or local crops cannot be excluded following the spreading of compost by an individual.
It recommends that these plastic materials be collected and then sorted by manufacturers with a view to receiving appropriate treatment (industrial composting, methanization, recycling, etc.).
Article written by Stéphane Leconte, scientific coordinator, Aurélie Mathieu-Huart, deputy head of the Evaluation of reference values and risks of chemical substances unit, and Isabelle Manière Guerrero, scientific coordinator at Anses.
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