Potable water is both a finite and renewable resource. While it is infinitely recyclable, the Earth’s stores of fresh water at any point are limited. So when humanity’s booming populations drain these reserves faster than they can be replenished, shit gets real. And this is how we fix it.
The best way to overcome our water deficit? Make some of that undrinkable H20 drinkable. The conventional methods for extracting the salt from seawater — evaporation ponds (like those above) and reverse osmosis plants — are both time-consuming and energy-intensive. These technologies were eclipsed last year when a Stanford Research team discovered it could cycle salt and fresh water through an electrochemical cell. And if you run the same system in reverse — that is, pumping electricity in rather than out — you can extract semi-fresh water at a fraction of the cost of conventional means
The Stanford Study discovered that the salinity difference between seawater and river water can be leveraged as a huge, renewable source of energy — if they can efficiently extract that potential energy. To do so, the team devised and fabricated a “mixing entropy battery”.
Per the study’s summary:
Here we demonstrate a device called “mixing entropy battery”, which can extract [the potential energy] and store it as useful electrochemical energy. The battery, containing a Na2−xMn5O10 nanorod electrode, was shown to extract energy from real seawater and river water and can be applied to a variety of salt waters. We demonstrated energy extraction efficiencies of up to 74%. Considering the flow rate of river water into oceans as the limiting factor, the renewable energy production could potentially reach 2 TW, or 13% of the current world energy consumption.
Basically, you take an electrochemical cell with a cathode made of silver and an anode made of manganese oxide nanorods. If you add some salt water to the cell and apply a current, that will attract and trap chlorine ions to the cathode and sodium ions (salt) to the anode. The desalinated water is then flushed from the system, more salt water is pumped in, and the current is stopped so that the chlorine and sodium ions slough off the electrodes, into the new batch water. This super-salty water is then disposed of as waste — presumably into the ocean — and the system is reset for the next round of desalinisation.
Granted, even at 74 per cent effectiveness, this system has a ways to go until it actually produces truly potable desalinated water (which has a maximum of 2 per cent sodium). But it also doesn’t require the massive pressures or temperatures other methods demand. And it may just be our best bet when Waterworld finally happens in real life. [ACS via Dvice]