Low energy water desalination with seawater greenhouse

Engineers at the University of Illinois have taken a step forward in developing a saltwater desalination process that is potentially cheaper than reverse osmosis and borrows from battery technology. In their study, the researchers are focusing on new materials that could make desalination of brackish waters economically desirable and energy efficient.

The need for practical desalinization technology is rising in the context of global climate change. Coastal regions, where the rise of seawater could encroach upon and contaminate groundwater aquifers, present just one area of concern. As demand for diminishing clean water sources increases, the need for desalination of lower-salinity brackish water from inland and industrial sources will increase, the researchers said.

Illinois mechanical science and engineering professor Kyle Smith and his co-authors have published a study demonstrating the viability of this batterylike technology in the journal Electrochimica Acta.

In a previous study, Smith and his co-authors used theoretical modeling to show that technology used in sodium-ion batteries may efficiently desalinate seawater. Their theory states that by using electrodes that contain sodium and chloride ions, salt is drawn out and held in a chamber separate from the purified water.

“In our new study, we constructed and experimented with a batterylike device that uses electrodes made from a different material. That material can remove from brackish water not only sodium ions but also potassium, calcium, magnesium and others,” Smith said. “This is important because salt and brackish waters do not contain just sodium chloride. It is often in a mix with other salts like potassium, calcium and manganese chloride.”

The new material is a chemical analog to the compound Prussian blue — the intense pigment used in ink for blueprints. It works by taking and holding positively charged ions like sodium within its crystal structure, Smith said.

“The competition between the rate of diffusion of the positively charged ion within the crystal structure and the volume at which the ions can be stored creates a traplike structure,” Smith said. “They go in easily but can’t get out.”

There are other materials that can secure positive ions, but the Prussian blue analog has an additional benefit — it is potentially very cheap to source.

“To make a technology like this be economically feasible, it needs to be cheap and, ideally, have some value-added benefit,” Smith said. “By showing that our device works well with lower-salinity waters, the door for use with inland brackish waters and possibly industrial wastewater has opened.”

Smith and his co-authors show that the amount of salt removal is sufficient to demonstrate their concept using brackish water. However, further research is needed to determine how the removal of salts from higher-salinity seawater and wastewater will impact that energy efficiency.

Slawomir Porada, Aniruddh Shrivastava, Pamela Bukowska, P.M. Biesheuvel, Kyle C. Smith. Nickel Hexacyanoferrate Electrodes for Continuous Cation Intercalation Desalination of Brackish WaterElectrochimica Acta, 2017; 255: 369 DOI: 10.1016/j.electacta.2017.09.137

University of Illinois at Urbana-Champaign. “New headway in desalination technology.” ScienceDaily. ScienceDaily, 12 October 2017. <www.sciencedaily.com/releases/2017/10/171012164001.htm>

February 16th, 2008 by , Clean Technica

greenhouse_wl_2423.jpgThree–hundred twenty-six million trillion! It sounds like a number I would come up with as a kid, say, in reference to the number of things I find disgusting about my sister, or the number of reasons I need a new bike, or the number of mosquito bites I got on a weekend camping trip. But, it turns out, 326 million trillion is a real number. It happens to be (approximately—because who could count them all?) the number of gallons of water on our wonderful planet (Earth). That’s an overwhelming, impressive and — when you learn that 98% of that water is ocean water, and therefore too salty to consume, or use for irrigation — frustrating figure!

In these times where climate chaos has caused more frequent severe droughts, and our population continues to grow (read: consume water) at an awesome rate, people are becoming more and more concerned with water conservation. Humanity finds itself increasingly at a loss for freshwater while roughly 315 million trillion gallons of unusable seawater taunts us from our shores.

Sure, desalination plants are becoming more common. They are very expensive, however, and so energy intensive that they only further contribute to the climate change they are attempting remedy (thereby, joining corn-based ethanol as the two largest non-solutions to our climate problems).

Fear not my fellow water-loving earthlings! There is an even better way to remove the salt from salt water: a Seawater Greenhouse! This UK-based company explains the process as one that:

uses seawater to cool and humidify the air that ventilates the greenhouse and sunlight to distill fresh water from seawater. This enables the year round cultivation of high value crops that would otherwise be difficult or impossible to grow in hot, arid (conditions).

The overall process produces water at the energy cost of less than 3kWh/m3. I can think of 326 million trillion reasons to get excited about this solution! For more information on the Seawater Greenhouse visit www.seawatergreenhouse.com.

Image: Seawater Greenhouse, Tenerife, Canary Islands. Source: Seawater Greenhouse Gallery