As part of the energy transition, France has been committed for several years to the development of methanization. As of January 1, 2020, there were just over 800 installations, compared to 75 in 2010.
This solution is interesting on a farm scale and makes it possible to recover waste and produce biogas. The agro-industry has recovered the model and today we are witnessing the establishment of methanizers, with industrial dimensions.
The process of methanization consists in producing methane gas (mixture of CO 2 and CH4) from agricultural waste (liquid manure, manure, cereal straw). The fermentation of the waste creates biogas, which is used for electricity, heat or biomethane, and organic residues, called digestate, which contains fertilizing materials.
For the soil specialist, Claude Bourguignon –  who joined the C.N.V.H. collective –  “It’s a disaster: the digestate no longer contains carbon. By spreading it, we lose the organic matter of the soil. We only feed the plants and not the soil: we will never make humus with it. The digestate does not bring any amendment on our soils which are today largely ruined. It is worse than liquid manure that is already too rich in nitrogen and too poor in carbon. He adds, “Methanization is anaerobic, without oxygen. It secretes acids and very dangerous germs! Their spreading can kill the soil organisms”. This phenomenon added to the nature of some methanized waste (sewage sludge, chemicals) raises concerns and raises risks of water pollution, even on health.
The scientific collective of the National Assembly in December 2020 –  was already concerned about the worrying and disastrous consequences of this model. It reported that “the nature of the accidents is varied and the environmental consequences are multiple. We note fires, explosions, gas emanations, run-off, water pollution, atmospheric discharges, with various causes, and consequences on the soil. Biodiversity is impacted since fish, insects, bees and earthworms die.
Odor and noise pollution on local residents (over distances of up to a few dozen kilometers since the digestate storage and spreading areas are also concerned) can have short and long-term consequences.
In the LOT (46) a major accident occurred in May 2021 (source: Confédération Paysanne). A 400 m3 tank of digestate spilled and infiltrated through the karstic soils. On these very fragile soils of the Causse in the Lot, the spilled digestate penetrated the thin layer of soil and then the limestone and polluted the water table.
This has not prevented the project leaders from developing 4 methanizers in the Lot (southwestern region of France) with large public subsidies, in addition to the one in Gramat, where numerous nuisances have been proven. It is about the following communes: Labathude, Espeyroux, Viazac and Gorses.
I live a few kilometers from one of these villages in Cardaillac, the digestate should be spread on the neighboring fields near our houses!
According to Daniel Chateigner – : “It is because the methanogenic power of plants is more important than animal waste. To avoid that too many crops are ingested by the methanizers, a law imposes to limit to 15 % the introduced waste coming from food crops”. But there is no control.
“This may increase our dependence on imported corn and soybeans from the Amazon,” says René Louail, a former regional councillor from Brittany.
The Confédération paysanne, adds that the farms already have more and more difficulties to get fodder because of the droughts, enter in competition with the methaniseurs. Its former spokesman for the agricultural union denounces “a land grab for energy production and defends the construction of small units.”
Citizen and scientific collectives alert on the risks incurred for the environment and the populations. We note the lack of public control before and after the commissioning of methanizers in the territories. In the Lot, the problem is all the more crucial as the soils are made up of a fragile soil, crossed by rivers whose quality is already threatened.
Many thanks to François Gillet, who gave me a lot of information on this subject.
 Claude Bourguignon – agricultural engineer in the magazine Sans Transition of September – October 2021.
 C.N.V.H. : Collectif National Vigilance Méthanisation
 Parliamentary commission of inquiry on the evaluation of public policies on environmental health. December 2020. Member of this commission Daniel Chateigner.
 Daniel Chateigner – professor of physics at the University of Caen and member of the C.S.N.M: Collectif National pour une Méthanisation raisonnée.
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