What if one of the solutions for slowing down coastal erosion lies in certain bacteria present in the marine environment, which have the ability to naturally produce limestone? While 22% of the 20,000 kilometers of the French coastline are subject to a decline in their coastline, according to the Ministry of Ecological Transitionthis is a very serious track studied for five years by a team of researchers from the University of La Rochelle.
“These biocalcifying marine bacteria have the ability, through their metabolic activity, to precipitate minerals, such as calcium and magnesium, explains Sophie Sablé, microbiologist at the littoral environment and society laboratory at the University of La Rochelle. They modify the conditions around it, including the pH of the water, and create the right conditions for this to allow the precipitation of calcium into limestone”.
Two processes combined to speed up the work of the elements
The problem is that this rock formation activity can take “several hundred or even thousands of years”, points out Marc Jeannin, materials physicist at the laboratory of engineering sciences for the environment, at the University of La Rochelle. To accelerate the slow work of the elements, the two researchers are counting on the combination of the most efficient marine bacteria (among 14 strains studied) with an electrochemical process which makes it possible to aggregate the limestone.
“We pass a low voltage electric current through a grid buried in the sediments, which will make it possible to manufacture a kind of natural cement to make artificial rocks, and to reinforce the anti-erosion structures”, explains Marc Jeannin. In the laboratory, the research team is already making “biobricks” with these bacteria. In one month, they already acquire the resistance of a mortar and their alliance with the electrochemical process therefore looks promising.
A full-scale test planned in two to five years
The idea is to come and consolidate the base of the works undermined by the process of scouring (digging at their bases) of the dykes, the riprap or even the devices of sand puddings. The method could also, at the cost of a more complex implementation device, relate to the feet of cliffs.
For now, there are no full-scale tests combining the electrochemical process with biocalcifying bacteria. “We don’t know how they will behave when concentrated, they shouldn’t disturb the local ecosystem, the fauna and flora, and that implies some precautions”, specifies Marc Jeannin. The two teacher-researchers who belong to a team of around ten people (for whom this is not the only activity), are planning a first test in the natural environment within two to five years, but this will obviously depend on funding. of this project.
There are also leads on the uptake of CO2 by this bacterial metabolism. A thesis co-funded by ADEME is in progress on the subject.