By Jean-Claude Bonnemere
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The conference given by two CNRS scientists of national notoriety, Gérard Fonty and Daniel Chateigner, On the subject of ” agricultural methanization a full house in Assieron October 1, 2022, on the occasion of the 10 Grim Reaper Festival.
“Two scientists who are authorities on the subject! » This is how Gérard Fonty, director of research emeritus of the CNRS, specialist in microbial ecology, president of GREFFE (scientific reflection and information group for sustainable development) (1) and Daniel Chateigner, professor at the University of Caen-Normandy, crystallographer, were introduced. Physicist and researcher at the Crystallography and Materials Science Laboratory (CRISMAT) of the CNRS and coordinator of the National Scientific Group for Reasoned Methanization (CSNM) (2). The first intervened in person, the second by video, both committed to presenting the challenges of anaerobic digestion for the coming years.
A civilizing challenge
Process of transforming organic matter into biogas, methane and carbon dioxide, just as it occurs naturally in marshes, in the digestive systems of man or animals, methanization has been configured as an industrial or semi-industrial process. -industrial. “without measuring all the repercussions for nature » the two scientists point out.
“Everything is much more complex than we want it to be known”insists Gérard Fonty, indicating that fermentation takes place in the presence of several thousand species of microbes. First observation: energy must be spent to bring the products subjected to methanization to a certain temperature level. So it is important to have a variety of inputs (agricultural effluents, waste from the food industry, slaughterhouses, washing water, sludge, etc.) that will produce various types of gas: methane, carbon dioxide, but also hydrogen sulfide. However, only methane is the desired energy source, hence the need to purify the produced gases to keep only methane. CO2, due to the effect of methanization, is therefore released into the air. “The biogas must be sanitized, hence the need to use a new source of energy, in order to complete this stage” Gerard Fonty says. Observing that anaerobic digestion in the agricultural environment is touted as a virtuous process and a source of income for farmers, the two scientists question the motivations for this approach and believe the question was poorly framed from the start. “We are facing challenges of civilization! » they affirm.
Why agricultural methanization is a problem
Manure, organic matter, is the result of what is digested… however, these elements alone cannot provide enough methane, hence the need to add vegetable matter or agri-food waste. . In addition, the digester must be heated and the biogas must be processed; “So many steps that consume energy and generate greenhouse gases”observe the scientists. If it is not a source of income for the farmer or the industrial company that operates it, the biogas plant is likely to generate various types of pollution: odors, leaks, breakdowns, volatilization of NH4 gas (toxic)… Other consequences, More difficult to measure, it is feared in the medium and long term, after the dispersion of the digestate: the degradation of soil biodiversity and the loss of its fertility, due to the risk of chronic diseases, in particular. “This process is not in line with sustainable development! » Gerard Fonty thunders. When it is asked if the digestates spread on the soil can be considered good fertilizers, it is argued that they are degraded elements and that the nitrogen in the digestates deprives the soil microorganisms of their functions, weakens the microbial diversity. “With the diffusion of digestate, the soil can only become poorer, its fertility can only decrease, it will be necessary to make inputs: methanization seems to be a competitor of the soil ecosystem and is not compatible with soil biodiversity » Gérard Fonty says loud and clear. “Making the soil an energy producer is not your calling! » adds Daniel Chatigner. Clear conclusion: Methanation undermines our food security and sovereignty; It is civilizing nonsense! Gerard Fonty concludes. “Feeding people remains the main objective of sustainable development, food the main objective with regard to health, but it is clear that agricultural methanization is not going in that direction” the two scientists continue. “Anaerobic digestion is a dead end” continues Daniel Chanteigner, believing that this process returns too much CO2 to the atmosphere, precisely when it is urgent to reduce it as much as possible.
There are 1,600 methanizers in France, a figure that should be increased to 7,000 (equivalent to the useful agricultural area of 8 departments) if we want to have this process to dispense with Russian gas. This implies that to make these methanizers work, it is necessary to incorporate the agricultural production of the plants. Already 370,000 ha of crops in France are dedicated to anaerobic digestion (cives or maize), that is, the equivalent of the useful agricultural surface of a department.
Daniel Chanteigner notes that solar panels produce 200 times more energy than biomass. In the Block there are more than 6 methanizers in operation and 108 are planned, for an average installation of one methanizer every 17 km. At the national level, 11 accidents in methanizers caused contamination of watercourses. Daniel Chanteigner reports a drop in organic carbon in the land and questions intensive agriculture, which methanation only makes worse. He ends by calling for subsidies to be given to those who strive to ensure sustainable and virtuous agriculture, instead of continuing towards a dead end! In his eyes: “Anaerobic digestion poses risks to our future”.
(1) GREFFE is an association dealing with the issue of sustainable development, relying mainly on scientific data. It allows a global approach to the problems dealt with from an unquestionable scientific point of view, thanks to the association of the different skills of its members in biology, ecology, agronomy, nutrition, geography, economic and social sciences, medicine, physics and chemistry. Its members are scientists from national and international institutions (CNRS, INRA, university, Research and Development Institute, ANSES, FAO).
(2) The CSNM has set itself the objective of reviewing all aspects of methanation that are the subject of thematic files validated by consensus by the CSNM scientists. These files show all the impasses made in the rush to implement this sector, which is also largely subsidized by the state and local authorities.
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