Cynthia Lopez of Mexico City had a question about seawater and drinking water.
Cynthia Lopez: As public water supplies become more scarce, what is the newest science for making saltwater more available?
EarthSky spoke to Tom Pankratz, independent consultant and a director of the International Desalination Association. Desalination is the process that makes saltwater fit to drink.
Tom Pankratz: As our traditional sources of water become less available, it’s necessary to turn to an alternative supply. And the only drought-proof supply, or the unlimited supply, is the sea. The problem is that removing the salt is a very expensive process.
In the past, desalination relied on boiling the water. But today’s newer techniques use a semi-permeable membrane.
Tom Pankratz: It’s a very thin plastic that allows only water molecules to pass through when it’s pumped to sufficient pressures. As the water passes through the membrane, the salt particles are left behind and then returned to the sea. The membrane is already effective, but the task now is to have the entire system operate at lower pressures and lower energy costs.
Pankratz said this technique is being used now mostly in the Middle East and Caribbean, as well as in the U.S. But Cynthia – in your hometown of Mexico City – this same technology could also be used to remove pollutants from city water supplies.
Our thanks to the Monsanto Fund, bridging the gap between people and their resources.
Our thanks to:
Tom Pankratz
International Desalination Association
Houston, TX
Photo Credit: Natsumi Kotsuki
I hope this will work but then agin I don’t hopefully you are susessful with the technology you have it should work
I hope this will work but then agin I don’t hopefully you are susessful with the technology you have it should work
If the more salt particles are left bact to the sea, is it possibly caused salt desnsity too high in the sea and destroy the oceans ecosystem?
James, that’s an important environmental issue that desalination scientists are dealing with. Concentrated seawater can damage marine ecosystems. Tom Pankratz told me that desalination plants mix the salt into the water as quickly as possible to dilute it and minimize the impact.
The problem with the traditional method of boiling water and saving and cooling the evaporate was that the desalination plant would also release a lot of hot water back into the sea. And as they drew seawater in, the desal plants would sometimes take in marine animals. Now plants are built with equipment to stop that from happening. But the major engineering problem is still the huge amount of energy that the desalination process uses.
So the environmental concerns with desalination are many, and that’s why scientists are working so hard to improve their methods.
Note that most of the desalted water will eventually get back to the ocean as sewage and seepage.
The first source of water to treat is treated sewage, as it is already low in salt. Then, turn to the ocean if available.