New methods can help solve the impending water crisis

Most people on the planet get their fresh water from lakes and rivers. But these only account for 0.007% of the world's water resources. As the population grows, so does the demand for fresh water. Now, two out of every three people in the world face severe water shortages for at least one month each year.

Other water sources-such as sea water and wastewater-can be used to meet the increasing demand for water. But these water sources are rich in salt and often contain pollutants such as toxic metals. Scientists and engineers have developed methods to remove salt and toxins from water. This process is called desalination.

But existing options are expensive and energy consuming, especially because they require many steps. Current desalination technologies also generate large amounts of waste-about half of the water entering some desalination plants will be lost due to wastewater containing all the removed salts and toxins.

I am a PhD student in chemical and biomolecular engineering. I am a member of the team that recently created a new water purification method. We hope that this method can make seawater desalination more effective, waste more manageable, and the scale of the water treatment plant smaller. This technology uses a new type of filter that can target and capture toxic metals while removing salt in the water.

In order to make a filter that can both capture metals and remove salts, my colleagues and I first needed a material that can remove many different pollutants (mainly heavy metals) from water.

For this, we turned to tiny absorbent particles called porous aromatic frameworks. These particles are designed to selectively capture individual pollutants. For example, one type of absorbent particles can only capture mercury. Other types specifically remove only copper, iron or boron.

Then I embedded these four different types of particles in a plastic film, basically creating a custom filter that can capture contaminants based on the type of particles I put in the film.

Then a colleague and I put these membrane filters into the electrodialysis water purifier. Electrodialysis is a method that uses electricity to separate salts and toxins from water and pass through membranes into a separate waste stream. This waste—often referred to as brine—can become toxic and expensive to treat in existing desalination processes.

In my team’s improvement process, called ion-trapping electrodialysis, we hope that membranes filled with tiny metal-absorbing particles can capture toxic metals instead of letting them enter the salt water.

This will achieve three benefits simultaneously in an energy-efficient manner:

Once our team has successfully manufactured these membranes, we need to test them.

The first test I conducted used a membrane filter embedded with a mercury capture absorbent to purify water from three sources containing mercury and salt: groundwater, brackish water, and industrial wastewater. What excites our team is that the membrane captured all the mercury in each test.

In addition, these membranes are also excellent at removing salt-more than 97% of the salt is removed from dirty water. Just pass through our new electrodialysis machine once and the water is completely drinkable. Importantly, further experiments have shown that mercury cannot pass through the filter until almost all the absorbent particles in the filter are used up.

Then my colleagues and I need to see if our ion trapping electrodialysis process is suitable for other common harmful metals. I tested three membrane filters containing copper, iron or boron absorbents.

Every filter is successful. Each filter can capture all target pollutants without any detectable pollutants entering the brine, and at the same time remove more than 96% of the salt from the water, purifying the water to usable conditions.

Our results show that our new water purification method can selectively capture many common pollutants while also removing salt in the water. But there are still other technical challenges to be solved.

We hope that our work will lead to new methods that can effectively purify water sources that are richer but more polluted than fresh water. The work is really worth it. After all, the impact of water scarcity is huge, both at the social level and at the global level.

This article was originally published in The Conversation by Adam Uliana at the University of California. Read the original article here.