Since July, I’ve been living in the South of France, exploring the local culture, geography and historic marvels. In the next few blogs, I’ll try to share some of the interesting engineering-related stories that I’ve uncovered. You can read about more of my ongoing adventures at http://mistralwriter.blogspot.com
Les Salins de Camargue
It’s said that the Roman engineer Peccius was the first to organize the salt production efforts in the Camargue, an area of southern France near the mouth of the Rhone River. The natural salt marshes and higher-than-normal natural salt content make the region an obvious place to harvest sea salt. Around the city of Aigues-Mortes, meaning “dead water,” 500,000 tons of salt are collected annually. While some of the process occurs naturally, capturing the quantities of salt demanded by human appetites requires an engineered process.
First, the salt is collected in vast evaporation pools. More than 45 million cubic meters of seawater must be pumped during the month of March. Throughout the spring, the evaporation process increases the concentration of salt 9-fold, to about 260 grams per liter. By mid-summer a thick cake begins to form on the surface of the water. The concentrated brine can grow to 20 cm thick, 9 cm of which is harvested as sea salt. The top of the cake takes on a bright red hue due to the presence of a special kind of algae that turns brighter as the salt concentration increases. Some of the algae and waste sediment can be collected and used as fertilizer. Lower quality salt is sold for road de-icing.
In September, the salt is harvested. Quality control measures ensure that the table salt is 99.5% pure sodium-chloride. Some salt is shipped on flat bottom barges along the shallow canals to the port, while another portion is loaded onto rail cars and sent in land. Several special bridges and conveyor systems are placed in service specifically for the once-a-year collection.
Having harvested salt from these marshes for over a thousand years, the Camargue salt farmers have struck a symbiotic balance with nature. While many industrial processes pose a threat to the local ecosystem, salt farming in the Aigue-Mortes salt marsh has actually led to greater preservation of the indigenous wetlands. Of course, the salt companies probably exaggerate the extent of this success. Nevertheless, this is a model for living sustainably with nature.