Having drinking water is a problem in a lot of places on Earth due to various reasons. One of the solutions for this is to extract drinking water out of sea water/salty water. Unfortunately, the traditional methods of doing this require a lot of power and that causes other issues. Plus, that means that we can’t setup the desalination plants in locations where they are most needed as these locations don’t usually have reliable power either. One solution is to use renewable energy such as Solar to power these plants but the traditional setups expect constant power levels which isn’t always possible due to weather conditions.
Around a 100 years ago we developed reverse osmosis and electrodialysis, which are two membrane-based desalination technologies. Reverse osmosis requires a lot of pre-treatment and thus not sustainable everywhere, which is why MIT researchers led by Jonathan Bessette decided to go with electrodialysis instead.
What makes their approach really interesting is that their setup runs on renewable energy (Solar Power) and automatically adjusts the quantity of water being processed depending on the weather conditions instead of expecting constant power levels. So if it was a sunny day with clear skies then the setup would process more water, and if it was cloudy the quantity being processed would reduce automatically.
The two most important parameters in electrodialysis desalination are the flow rate of the water and the power you apply to the electrodes. To make the process efficient, you need to match those two. The advantage of electrodialysis is that it can operate at different power levels. When you have more available power, you can just pump more water through the system. When you have less power, you can slow the system down by reducing the water flow rate. You’ll produce less freshwater, but you won’t break anything this way.
Bessette’s team simplified the control down to two feedback loops. The first outer loop was tracking the power coming from the solar panels. On a sunny day, when the panels generated plenty of power, it fed more water into the system; when there was less power, it fed less water. The second inner loop tracked flow rate. When the flow rate was high, it applied more power to the electrodes; when it was low, it applied less power. The trick was to apply maximum available power while avoiding splitting the water into hydrogen and oxygen.
The prototype unit they setup was the size of a shipping container and over the 6 months trial period it desalinated around 5,000 liters of water per day—enough for a community of roughly 2,000 people. The team is now working on productionalizing the solution and selling it commercially.
Their work was published in Nature: Direct-drive photovoltaic electrodialysis via flow-commanded current control, earlier this month.
Looking forward to people building on top of this effort and having such units available for purchase.
Source: Mastodon: https://mstdn.social/@kevinrns/113341185649409458