Using a standard technology, we could produce desalinized water at a cheaper and simpler rate than we already do.
That is, University of Illinois engineers found in a study that we could run electricity through a salt water-filled battery to remove salt ions from the water. Voila, simple water desalinization, say the researchers.
"We are developing a device that will use the materials in batteries to take salt out of water with the smallest amount of energy that we can," said Kyle Smith, a mechanical science and engineering professor at Illinois who authored the study with graduate student Rylan Dmello Smith. "One thing I'm excited about is that by publishing this paper, we're introducing a new type of device to the battery community and to the desalination community," continued (Kyle) Smith. Smith is the only one of the two who will be quoted in this article.
As drought becomes a greater concern, water desalinization technology interest has risen. But putting together a wide-scale system has been slowed by technical obstacles and the sheer amount of energy required. Reverse osmosis is the most common method, and it is an expensive and energy-heavy process that pushes water through a membrane tight enough to remove the salt.
The new research was inspired by sodium ion batteries, a type that contains salt water. In those batteries there are two chambers, a negative electrode and a positive one. Between the two is a separator - ions can move across it. The battery's discharge causes the chloride and sodium ions (those two salt elements) to move into one chamber. The salt-free water is left in the other.
Normally in such a battery, when the current flows in the other direction, the ions diffuse back to their previous combined state. But in this study, the Illinois researchers figured out how to keep the salt from rejoining the water.
"In a conventional battery, the separator allows salt to diffuse from the positive electrode into the negative electrode," said Smith. "That limits how much salt depletion can occur. We put a membrane that blocks sodium between the two electrodes, so we could keep it out of the side that's desalinated."
There are several ways that using a battery in this way is simpler than reverse osmosis. Such a battery can be small or large. It can therefore adapt to various applications. By contrast, reverse osmosis plants need to be large in scale in order to be cost effective and efficient, noted Smith. Because the battery system only needs water to flow over the electrodes, not be forced through a membrane, it requires less pressure and therefore less energy. With the battery, energy used is fairly close to that required by nature, said Smith. It's also possible to adjust fairly easily the water rate as it slows through the battery - more so than for desalinization methods that have more complex plumbing.
In a test to see how the battery performed on seawater or similar salt concentrations, Smith and Dmello Smith discovered that their device could produce about 80 percent desalinated water. While their modeling doesn't yet consider other water contaminants, they are aiming to do a series of experiments with real seawater.
"We believe there's a lot of promise," Smith said. "There's a lot of work that's gone on in developing new materials for sodium ion batteries. We hope our work could spur researchers in that area to investigate new materials for desalination. We're excited to see what kind of doors this might open."
The results were published in the Journal of the Electrochemical Society.
