Using Green to Combat Saline: Testing Salt-Tolerant Algae as a Desalination Method

By Christina Burchette

In 2014, the Lawrence Berkeley National Lab Institute for Globally Transformative Technologies released a report called “The 50 most critical scientific & technological breakthroughs required for sustainable global development.” Of all the technologies the report highlighted, the number one priority on the list was a new method for desalinating water. That’s because water security is closely linked with energy and food security issues—world water demand is rising, and more than 70% is used for agriculture.

Algae water sample, desalinated sample, desalinated and filtered water sample

From left: Desalinated and filtered water sample, desalinated water sample, algae water sample

There is a large volume of brackish water (salt water and fresh water mixed together) in many arid areas of the world, but current desalination methods are expensive and use a lot of energy, which means that most people who need them can’t use them. Finding a low-cost and renewable desalination method could help alleviate some of the effects of water scarcity, which is becoming an increasingly apparent problem as we continue to feel the impacts of climate change around the world.

So how do we find a sustainable, low-cost, and energy efficient way to remove salinity from water, making it suitable for drinking and agriculture? By harnessing the power of the ultimate technology: Mother Nature. Recently, some of our scientists investigated the use of salt tolerant algae—also known as halophytic algae—as a natural and sustainable method to decrease salinity in brackish water and seawater. Some species of salt-tolerant algae can absorb up to 50 times more salt than the concentration of salt in the water they inhabit, making them a perfect (and natural!) way to desalinate water for potable use. In addition, the growing algae can be used to mitigate carbon dioxide from point source emissions. Once the algae has been used for desalination, it can then be harvested and used as a raw material for biofuel production to reduce the use of fossil fuels.

The photobioreactor looks like a large glass tube

The photobioreactor

To gather insight about which algae species would perform the best during experiments, researchers visited an algae bank at the University of Texas at Austin. After screening more than 12 different types of algae species and noting special conditions like pH, micronutrient requirements, and light cycle sensitivity, researchers picked four types of halophytic algae that had the best salt uptake rates.

They then grew and tested the algae for its salt-removal capabilities in a photobioreactor, which is a vessel that housed the algae and provided it with the light it needed to mature. Researchers manipulated the algae’s breeding and feeding conditions to optimize growth rate, survival rate, and absorbency and discovered that they could remove up to 30% salinity in brackish water samples in one treatment stage.

While complete desalination can’t be achieved with algae alone, this method can serve as a pretreatment to other desalination technologies—reducing the energy footprint and financial costs of desalination while making the process more sustainable. EPA researchers are currently comparing the sustainability advantages of biodesalination technology with conventional approaches. This research highlights not only what our researchers are doing to provide potential solutions to global water issues, but also the amazing things that can be achieved with natural resources and a little bit of science.

Various algae species in smaller bioreactors

Various algae species in smaller bioreactors

About the Author: Christina Burchette is an Oak Ridge Associated Universities contractor and writer for the science communication team in EPA’s Office of Research and Development.

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