Thrown into our trash, what is this resource that could be reused?
2024-01-21 08:00:00
Question from Marc, Solliès-Pont
“When we see everything that is in our trash, all the kitchen scraps, we say to ourselves: it’s enough to throw away a material that could be used in a short circuit.”
Thank you Marc, from Solliès-Pont (Var), for this remark which raises a very current question. Since January 1, 2024, local authorities are supposed to allow the sorting of bio-waste. So that they are no longer thrown into the household waste bin.
Despite its entry into force, application of the law remains limited, since equipment (composters or collectors) is frankly rare. As for individuals, although they are encouraged to sort, they are not directly targeted by the obligation. Marc-André Selosse regrets it because, insists the professor, “biowaste is a resource”.
Are you still doubtful? So, look what’s happening in the ground…
1. I weigh 5 tonnes/hectare, who am I?
“Generally speaking, we are quite cut off from nature.” The speaker is a professor at the National Museum of Natural History. Microbiologist, Marc-André Selosse has a passion, “the ground that we trample” and who is yet “the origin of the world”.
This universe is rich with unsuspected life, “the workers of the soil, microscopic, even amoebas and bacteria which are not visible to the naked eye. But there are many of them!”
A numerical illustration to see this. “In one hectare of soil, there are 1.5 tonnes of animals, 5 tonnes of roots… and 5 tonnes of microbes.”
This is an overview of the environment where biowaste, plant waste, feels like home. Whether from the composter at the bottom of the garden, or from the collector of your co-ownership, or your municipality (if there is one!).
Marc-André Selosse, microbiologist, professor at the National Museum of Natural HistoryPhot DR Quentin Houdas – Leextra.
2. What’s in my waste?
In addition to the carbon contained in the plant mass, “Organic waste contains nitrogen, phosphorus, potassium, in short, everything that farmers buy and put in their fields each year. These are potential fertilizers”.
All of these natural compounds are basic nutrients for plant growth.
Another example, smile, urine is a super fertilizer. “With 4 grams of nitrogen per liter and 0.5 grams of phosphorus, it is even a pure fertilizer”illustrates Marc-André Selosse, not stingy with references to “mother poops”in the novel La Terre by Émile Zola. “You know, the one with the prettiest cabbages on the market.” In comparison, “mineral fertilizers are imperfect, because they are harmful to health and harmful to greenhouse gases..
3. So, shall we sort?
“Today, there is a constraint, which people do not see. Our money is used to burn garbage. We squander organic matter, with our taxes. We lose all the nitrogen and phosphate that organic matter contains , while farmers buy fertilizers. Fertilizers that are not renewable.”
The scientist believes that “we live on credit”. Or, “taking time to sort your organic waste after a meal is a gesture of love. For your children!” A bit provocative, he adds: “You have to love your children.”
4. How does this relate to climate?
In the soil, organic matter has several roles, “essential functions”.
“It sticks the soil particles together, which structures the soil and makes it more stable.” So even a porous floor does not collapse.
Organic matter “has an affinity for water and is able to store it”. This is why rich soil will absorb rain, much more than intensively cultivated soil deprived of its nutrients. Sadly, this is often the case. In 50 years, “French soils have lost half of their organic matter. They are half as rich”.
Finally, “this material stores carbon”even if the ground also gives off gas. “The idea, adds Marc-André Selosse, is that this will happen over a long time. Especially if we plow little. This is carbon storage over 100, 150 or even 200 years.”
that’s why “replenishing the stock of organic matter in the soil is good for the climate, good for water reserves and against erosion”.
5. Is there a cultural problem?
“Historically, it is first and foremost a cultural problem, tells Marc-André Selosse. The ground is opaque. In people’s minds, the floor is dirty, it soils the shoes. We bury the corpses in the ground.”
These ancient prejudices resulted in “a lack of interest, including in science and university, until the 1990s”.
It is on the side of changing mentalities that Marc-André Selosse insists, anxious to make “understand living things and their mechanisms”. On its scale, plant waste (food or green waste) allows us to understand a bit of it.
Marc-André Selosse is president of the Biogee Federation, sciences for society, which promotes information on life sciences. He is the author of several books and has provided scientific advice for comics Undergroundpublished by Éditions Dargaud.