MIT engineers invent new method to eliminate lead from drinking water

U.S – Engineers at the Massachusetts Institute of Technology (MIT) have developed a new approach to removing lead and other heavy-metal contaminants from water, in a process that they claim to be far more energy-efficient than any other currently used system.

The engineers say the process is much more effective than current methods of lead removal, as it does not target sodium and magnesium which are essential to healthy drinking water. Ultimately, it might be used to treat lead-contaminated water supplies at the home level, or contaminated water from some chemical or industrial processes.

The new system is the latest in a series of applications based on initial findings six years ago by members of the same research team, initially developed for desalination of seawater or brackish water, and later adapted for removing radioactive compounds from the cooling water of nuclear power plants. The new version is the first such method that might be applicable for treating household water supplies, as well as industrial uses.

The findings have been published in the journal Environmental Science and Technology – Water, in a paper by MIT graduate students Huanhuan Tian, Mohammad Alkhadra, and Kameron Conforti, and professor of chemical engineering Martin Bazant.

“It’s notoriously difficult to remove toxic heavy metal that’s persistent and present in a lot of different water sources. Obviously, there are competing methods today that do this function, so it’s a matter of which method can do it at a lower cost and more reliably,” Alkhadra says.

The biggest challenge in trying to eliminate lead is that it is generally present in such tiny concentrations, vastly exceeded by other elements or compounds. For example, sodium is typically present in drinking water at a concentration of tens of parts per million (ppm), whereas lead can be highly toxic at just a few parts per billion (ppb). Alkhadra explains that most existing processes, such as reverse osmosis or distillation, remove everything at once. This not only consumes much more energy than would be needed for a selective removal, but it’s also counterproductive since small amounts of elements such as sodium and magnesium are actually essential for healthy drinking water.

The biggest challenge in trying to eliminate lead is that it is generally present in such tiny concentrations, vastly exceeded by other elements or compounds. For example, sodium is typically present in drinking water at a concentration of tens of parts per million (ppm), whereas lead can be highly toxic at just a few parts per billion (ppb). Alkhadra explains that most existing processes, such as reverse osmosis or distillation, remove everything at once. This not only consumes much more energy than would be needed for a selective removal, but it’s also counterproductive since small amounts of elements such as sodium and magnesium are actually essential for healthy drinking water.

The new approach uses a process called shock electrodialysis, in which an electric field is used to produce a shockwave inside an electrically charged porous material carrying the contaminated water. The shock wave propagates from one side to the other as the voltage increases, leaving behind a zone where the metal ions are depleted, and separating the feed stream into a brine and a fresh stream. Researchers say the process results in a 95 percent reduction of lead from the outgoing fresh stream.

“In principle, this makes the process much cheaper because the electrical energy that you’re putting in to do the separation is really going after the high-value target, which is the lead. You’re not wasting a lot of energy removing the sodium. As the lead is present at such low concentration, less current is involved in removing those ions, so this can be a very cost-effective way.”

However, as with every new invention, the process still has its limitations, since it has only been demonstrated at small laboratory scale and at quite slow flow rates. New Food Magazine reports that scaling up the process to make it practical for in-home use will require further research, and larger-scale industrial uses will take even longer. Bazant informs that the approach could be practical within a few years for some home-based systems.

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