Lockheed Martin Developing Desalination Method That Uses Much Less Energy Than Reverse Osmosis
March 18th, 2013Via: Reuters:
A defense contractor better known for building jet fighters and lethal missiles says it has found a way to slash the amount of energy needed to remove salt from seawater, potentially making it vastly cheaper to produce clean water at a time when scarcity has become a global security issue.
The process, officials and engineers at Lockheed Martin Corp say, would enable filter manufacturers to produce thin carbon membranes with regular holes about a nanometer in size that are large enough to allow water to pass through but small enough to block the molecules of salt in seawater. A nanometer is a billionth of a meter.
Because the sheets of pure carbon known as graphene are so thin – just one atom in thickness – it takes much less energy to push the seawater through the filter with the force required to separate the salt from the water, they said.
The development could spare underdeveloped countries from having to build exotic, expensive pumping stations needed in plants that use a desalination process called reverse osmosis.
“It’s 500 times thinner than the best filter on the market today and a thousand times stronger,” said John Stetson, the engineer who has been working on the idea. “The energy that’s required and the pressure that’s required to filter salt is approximately 100 times less.”
Correct me if I’m being a doomcryer, but every time I read about a largescale desalinating process I wonder what’s to be done with the left over salt.
It seems to me that the aforementioned underdeveloped countries won’t have much ability to store or safely dispose of “waste” salt, so it would probably go straight back into the ocean.
I know the oceans seem big enough to be pretty safe against some extra salt, but even saltwater marine life has limits to how much salt they can handle, especially while their environment’s temperature and ph balance are also changing pretty drastically.
I’d be interested to see any projections on this subject, if they exist.
The brine is generally sent back out to sea. Here’s something from a FAQ:
What happens to the salt that is removed from the water?
In reverse osmosis, salt water on one side of a semi-permeable membrane is subjected to pressure, causing fresh water to diffuse through the membrane leaving behind a concentrate stream. The concentrate stream contains the majority of the dissolved minerals and other contaminants, which needs to be safely disposed off.
Concentrate management can become one of the most important factors in determining the feasibility of a plant. Concentrate produced during seawater desalination can be disposed through deep well injection on land or returned to the ocean in a controlled process to avoid detrimental effect to the environment or marine life. For concentrates produced in inland facilities, a few other options exist. These include disposal to surface water bodies, evaporation ponds, or to wastewater treatment plants. In some instances, the concentrate can also be utilized beneficially for industrial processes.