Battery turns saltwater into drinking water
tech.slashdot.org
tech.slashdot.org
Also here's the catch/
"The desalinated water that comes from the battery still contains too much salt for drinking, La Mantia says: “We removed up to 50% of the original salt, but we need to arrive at 98%."
actual paper if you have access: http://pubs.acs.org/doi/abs/10.1021/nl203889e
There are proposals to mix freshwater from the mouth of streams with seawater and capture the energy released.
Yes, the osmotic pressure is similar to a head of about 240 meter. In practice it will be less in practice (110-120m), but still significant.
> There are proposals to mix freshwater from the mouth of streams with seawater and capture the energy released.
Not only proposals, but there is a prototype in production on Norway that opened in 2008.
http://www.statkraft.com/energy-sources/osmotic-power/
I think the problem for such power plants is to make the membranes efficient enough, and given that they have problem to remove all salt in this "battery", I guess that they have the same problem. For reverse osmosis I'm pretty sure it is more efficient with lower gradient, so these techniques could be combined.
Since osmotic power is better with larger salt gradients, a power plant that use the gradient between the ocean and the Dead Sea would be perfect. The Dead Sea sinks one meter per year because of excessive use of water for irrigation. There is probably not the right political climate in the area to achieve such things however.
There are already plans to collect energy from the elevation drop - adding the salinity change too could be pretty nice. This seems like a rare environmental win - get free energy, and replenish the water level at the same time.