With more than 22,000 factories around the world, this activity is growing more and more, particularly in the countries of the Arabian Peninsula. Among the techniques used, reverse osmosis is the most widespread today.
Seawater began to be desalinated industrially for human consumption in the 1930s. Since then, supply and demand have exploded, techniques have evolved significantly, and researchers continue to work.
In 2022, nearly 22,800 installations worldwide supplied approximately 110 million cubic meters of water per day, according to the International Desalination and Reuse Association. With growth of 6% to 12% per year, according to the report from the French Institute of International Relations Geopolitics of seawater desalination (September 2022). The latter also indicates that 90% of Kuwait’s water comes from such plants, 86% for Oman, and 70% for Saudi Arabia.
In research, more than 4,000 articles have been published each year since 2020 on desalination, according to the Scopus database. And, notably, in the top 6 of the most active institutions on this subject in terms of number of contributions, Saudi Arabia places three of its universities: King Fahd University of Petroleum and Minerals (3rd), King Abdullah University of Science and Technology (4th) and King Saud University (6th). China is the leading contributing country, ahead of the United States.
The three main methods of desalination Electrodialysis Distillation Reverse osmosis
Expensive large-scale deployment but ideal for low volumes Electrodes on either side of a tank attract salt ions, negative chlorides and positive sodiums, into two compartments, in order to purify the water. Portable systems for defense or humanitarian work have been developed. Energy cost Technical complexity Number of installations Floating solids SandCoal Positive electrode attracting chlorine ions Brine Brine Negative electrode attracting sodium ions Pumping station Sea water (containing on average 3.5% salt) is pumped far from the coast.
To avoid catching fish, pumping speeds are reduced. Filtration grid The first filters block the largest solids (debris, marine organisms, silt, etc.). Sand filtration Water circulates through sand and carbon to filter the finest materials. Desalination Salt is composed of negative chloride ions (Cl–) and positive sodium ions (Na+). For human consumption of water, their presence must be reduced to less than 0.05%. Remineralization To limit the attack by “pure” water on concrete pipes, calcium is added. This rebalancing of minerals also makes the water suitable for consumption. Distribution Disinfection products are optionally added to complete the process. Infographic: Le Monde, Victoria Denys and David Larousserie Sources: IDRA, VEOLIA This research has notably enabled considerable gains in efficiency. Distillation, a pioneering process in desalination, has been supplanted by the family of membranes, in particular by the technique known as “reverse osmosis”, which represents 70% of the market, compared to 25% for the first.
Gains in selectivity and permeability In the 1970s, reverse osmosis plants consumed more than 15 kilowatt hours (kWh) to produce 1 cubic meter of water. Today, they use between 2 and 3 kWh (for a theoretical minimum of 1 kWh), for a cost of 0.50 dollars (0.47 euros) per cubic meter for the largest installations. According to the spokesperson for Veolia, world leader in the field with more than 2,300 installations, the priority of the multinational’s research and development aims, despite this progress, to “reduce consumption and help its customers achieve their sobriety objectives . Above all, the group intends to accelerate the reuse of wastewater, which is still under-exploited.” Read also: Drinking water: a membrane that filters and creates electricity at the same time During distillation (multiple effects or staged expansions), energy is used to vaporize the water, which, by condensing, becomes a less salty liquid. For its part, the reverse osmosis technique is used to counter the natural phenomenon whereby water circulates from areas with the least concentration of minerals to the most concentrated areas. Pressure is applied to force the water through membranes that retain the salts.
The latter were made of cellulose acetate, before being replaced by more “selective” polyamides, that is to say blocking salts, thanks to a thin reactive layer, and also more permeable to water, thanks to many pores. These membranes are wound on long cylinders to maximize the exchange surfaces. MORE AFTER THIS ADVERTISEMENT Progress is not over, because gains in selectivity and permeability are still possible, but above all to respond to a persistent problem: these membranes become dirty due to various deposits (organic or salts), losing their effectiveness. They must therefore be cleaned, which requires often polluting chemicals which are found in the effluent and must therefore be treated. Chemists are seeking to develop non-dirty membranes, preventing the adhesion of deposits. Read also: The desalination of sea water is booming despite its environmental cost But this does not prevent the discharge from such a plant, a brine particularly concentrated in salt and various products used during treatment, being ultimately dumped at sea, posing additional environmental problems.
