Berkeley (USA), June 4 (The Conversation) Most people on Earth get fresh water from lakes and rivers. But these account for only 0.007 percent of the world’s water reserves.
With the increase in the human population on the earth, the demand for fresh water has also increased. Now, two out of every three people in the world face a severe water shortage for at least one month in a year.
Other water sources – such as seawater and wastewater – can be used to meet
But existing alternatives are expensive and consume more energy, as these processes have multiple steps. Current water purification technology also generates a lot of waste – some desalination plants waste almost half of the water used, with all the salts and toxins removed from the contaminated water.
I am a doctoral student in chemical and biomolecular engineering and am part of a team that recently created a new water-purification method that, we hope, can make desalination more efficient, reducing the amount of waste in water It can be easier to manage and water treatment plants can be smaller in size. This technology has a new type of filter that can also remove toxic metals while removing salt from water at the same time.
Creating an All-in-One Filter
To create a single filter that could remove metals and salts, my colleagues and I first needed a material that could remove various contaminants—mostly heavy metals—from water. To do this, we turned to smaller, absorbent particles.
These mesh particles are designed to selectively separate each contaminant from the water. For example, one type of absorbent particle can only hold mercury.
Other types of particles specifically separate only copper, iron or boron from water. Then I applied these four different types of particles to a thin plastic shell. This created a conventional filter that would capture contaminants according to the type of particulate I put in the shell.
I, along with a colleague, put this shell filter in an electrodialysis water purifier. Electrodialysis is a method that uses electricity to pull salts and toxins from water across a membrane and into a separate waste stream. Existing desalination processes to separate this waste – often called brackish or saltwater – substance from water can be toxic and costly.
In my team’s modified process, called ion-capture electrodialysis, we hoped that the shell bound with tiny metal-absorbing particles would capture the toxic metals and prevent them from getting into the salt water.
It will achieve three benefits in an energy-saving way at the same time: salt and metal will be removed from the water; Toxic metals will be captured in a small, easily disposed membrane – or potentially even reused; And the salty waste stream will be free of toxic substances.
How effective is ion-capture electrodialysis?
Our team successfully made these membranes, so we needed to test them. The first test I conducted was using membrane filters with mercury-catching absorbent particles to purify water that contained both mercury and salt from three sources—groundwater, brackish water, and industrial wastewater.
Our team was excited to see that the membranes separated all mercury particles from the water in each test. Additionally, the membrane was also very good at getting rid of salt – more than 97% was removed with dirty water.
After passing through our new electrodialysis machine only once, the water was completely potable. Importantly, further experiments showed that no mercury could pass through the filter until almost all of the filter’s absorbent particles were used up.
My colleagues and I now needed to see if our ion-capture electrodialysis process would work on other common harmful metals. I tested three membrane filters that contained absorbers for either copper, iron or boron. Every filter was successful. Each filter captured all the target pollutants present in the water, as well as removing more than 96% of the salts from the water, purifying the water enough to be used.
Our results suggest that our new water purification method can selectively capture many common contaminants while removing salt from water. But there are still other technical challenges to be explored.
First of all, the mesh absorbent particulates that selectively detect targeted pollutants that my colleagues and I put into the shell are too expensive to put into mass-produced filters. It is possible to place a cheap – but low-quality – absorber into the filter instead, but this may impair the filter’s water purification efficiency.
Second, engineers like me still need to test ion-capture electrodialysis technology at scales larger than those used in the laboratory. Many issues can often come up when moving any new technology from laboratory to industry.
Finally, water treatment plant engineers will need to devise ways to stop the process just before the membrane absorbance is maxed out. Otherwise, toxic pollutants will begin to seep through the filter into the salty wastewater.
Engineers could then restart the process after replacing the filter or removing the metals from the filter and collecting them as separate waste.
We hope that our work will lead to new methods that can efficiently and effectively purify available water sources that are more abundant – but more contaminated – than fresh water. This work is really of great importance. After all, the effects of water scarcity are enormous, both on a social and worldwide level.
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