It is a large-scale plan that is being deployed in our countryside. In order to reduce dependence on petroleum products, the energy transition law sets the objective that 10% of gas be of renewable origin in 20. This will represent 12 million tonnes of CO2 avoided per year (3% of our shows). In the Grand-Est region, this results in the doubling of anaerobic digestion units from 180 to nearly 400 if we follow the regional biomass shema. “Industrialization“denounced by the LPO, FNE-Grand-Est and the Confédération Paysanne. Due to the risk of water and soil pollution. At the same time, the chamber of agriculture of Meurthe-et-Moselle is setting up a charter of good practices for a more virtuous methanation.
Livestock effluents transformed into fertilizer and green gas
The initial idea is good: to use livestock effluents – which are waste – and by-products of agriculture and of intermediate dedicated crops for energy recovery, cultivated between two corn. The bacteria contained in the effluents will transform the organic matter to produce gas, in particular methane. This biogas can either be reinjected into the gas networks or produce electricity by cogeneration.
What remains after processing is called digestate, a fertilizer rich in nitrogen, phosphorus and microorganisms, which is intended to be spread on the fields to fertilize the soil. Clearly, it is a permanently available fertilizer which should in principle replace chemical nitrogenous mineral fertilizers, that is to say “not to be spread in addition, and especially at the right time “ specifies Philippe Goetghebeur, of the Water Agency.
The remains of the digesters should be applied at the right time and instead of mineral nitrogen fertilizers, not on top of that.
Indeed, “the digestate must be supplied at the right time, that is to say when the plant needs it for its growth and is able to absorb it “, explains Cosette Perez, adviser to the Chamber of Agriculture of Meurthe-et-Moselle.
However, the Rhine Meuse Water Agency notes that some, to get rid of the overflow of digestate, do not hesitate to spread on bare soil, thus causing nitrate pollution in waterways. This is particularly the case with the Rupt de Mad, where peaks at 180 mg / l have been observed on several occasions, while the threshold for drinking water is limited to 50 mg / l.
The Water Agency asks that good anaerobic digestion practices be observed to avoid pollution peaks in the water
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To limit this pollution, the law imposes a storage of digestates of four months, “linsufficient money with regard to the Chamber of Agriculture of Meurthe et Moselle “.
Cosette Perez, advisor in charge of the case, explains to us that “the projects carried out by the chamber systematically recommend storage ranging from six to eight months, to avoid spreading the digestate between September and February. ” This is particularly the case with the Valbioenergie biogas plant near Briey, which has a storage capacity of seven months and which we went to visit.
The disappearance of meadows to cultivate cereals
The other phenomenon that worries the Water Agency and environmental protection associations is the turning over of the meadows to plant cereals that will feed the methanizers.
Indeed, the meadows are buffer zones which capture nitrates, but also, very importantly, CO2. They do not require any input of fertilizers or pesticides. They therefore play an essential role in the fight against global warming and the preservation of soil and biodiversity.
The Water Agency has been investing for several years in aid plans for farmers for the preservation of grasslands, particularly in the water catchment sectors. She is worried to see her efforts reduced to nothing if the breeders abandon breeding for the cultivation of cereals dedicated to methanization. A much less restrictive and much more remunerative activity, as has happened in Germany.
To limit this drift, a decree of July 7, 2016 prohibits the intake of cereals dedicated to food (such as corn) at 15% of what goes into the methanizer.
For its part, Ademe is today suspending the allocation of its subsidies for new projects to the use for 60% of livestock effluents. Important safeguards, but which do not apply to all projects that were carried out before 2017, nor to those that do not request grants. And this is what poses a problem for France Nature Environment Grand-Est and the LPO and the Confédération Paysanne.
The gold Rush
Because making biogas is now proving to be very profitable. Not only is the resale price of gas nearly five times higher than that of natural gas, but the prices are fixed for 15 years, which gives farmers the assurance of having a fixed income. A strong argument, and we understand them, for abused farmers, in the midst of the livestock crisis, and who are struggling to make ends meet at the end of the month.
But for the methanizer to work well, it needs so-called methanogenic cultures, which produce a lot of energy and make the system profitable. Maize, rye, sorghum and rapeseed will become the new yellow gold of tomorrow.
The risk is when the farms which built the methanizers are not independent in cereals. They will then buy the material in other farms and do not hesitate to raise the prices, to the detriment of small breeders who no longer have the means to buy to feed the animals.
This is already observed by Jean-François Fleck, president of Vosges Nature Environnement in his department.
“Doubling the anaerobic digestion units will increase this pressure on biomass. It will take many more crops tomorrow to feed the digesters than we have today.“.
At the Meurthe-et-Moselle Chamber of Agriculture, we are trying to curb the problem by asking project leaders to reflect in order to be autonomous for everything that will fit into the anaerobic digestion unit, while retaining the meadows.
So, if we take the Valbioenergy project in Briey as an example, there is no entry of cereals from other farms. The farmers chose to keep the grasslands and not to use corn for gas.
On the other hand, they produce intermediate crops such as rye and sorghum, between two maize, for the digester. “These are so-called low-input crops, which do not need pesticides to grow and eradicate weeds for the next crop.“explains one of the associate farmers Dominique Hirtzberger.
What about the quality of the soil?
Another point of tension around anaerobic digestion: the quality of the soils on which the digestate is spread. It has so far been cited by the government as a miracle fertilizer, rich in nitrogen and which does not smell bad, which is partly true.
Except that a small number of independent scientists are sounding the alarm, such as the National Scientific Collective for Reasoned Methanization. The CNSM describes digestate as a poor quality fertilizer because it extracts most of the carbonaceous matter from inputs to produce gas, only to deposit nitrogen in the form of ammonium on the ground. Crops under this fertilizer will have to draw carbon from soil reserves. These will then take a hundred to a thousand years to reconstitute.
A fact that notes Rémy Toussaint, farmer in Reillon (Meurthe-et-Moselle) and member of the Confédération Paysanne. After embarking on anaerobic digestion six years ago, it is in the process of going backwards. He only spreads slurry digestates on his meadows and keeps the manure for his cereals. He co-signed the moratorium request with France Nature Environnement Grand-Est and the LPO.
At the Chamber of Agriculture 54, we are told that when there is a lot of livestock effluents, including manure, there is still carbon left to feed the soil. But experiments are being carried out in parallel to check whether the soils are not impoverished.
We are still far from knowing everything, nor from mastering everything about the effects of large-scale anaerobic digestion. What is certain is that time for reflection seems necessary in order to better regulate anaerobic digestion and that it is effectively virtuous and responds well to the objectives set, without once again destroying our environment.
This is what deputy Dominique Potier asked in an amendment tabled in 2019 and within the framework of the current Climate Law. Amendment rejected…
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