Removing lead from drinking water in an energy-efficient way

A relatively low-cost, energy-efficient approach to treating water contaminated with heavy metals.

MIT engineers have developed a new way to remove lead and other heavy metal contaminants from water. This new way is more energy-efficient and cost-effective.

The new way uses a process called shock electrodialysis.

Removing toxic heavy metals is quite tricky in a lot of different water sources. Undoubtedly, there are multiple methods to do this function, so it’s a matter of which method can do it at a lower cost and more reliably.

The biggest challenge in removing leads is the lead is generally present in such tiny concentrations. What’s more, it is vastly exceeded by other elements or compounds.

Usually, sodium is present in drinking water at a concentration of tens of parts per million, whereas lead can be highly toxic at just a few parts per billion.

Reverse osmosis or distillation are commonly used methods to purify and remove hazardous particles from water at once. This not only takes much more energy than would be needed for selective removal, but it’s counterproductive since small amounts of elements such as sodium and magnesium are essential for healthy drinking water.

In the process of electrodialysis, an electric field is used to produce a shockwave inside a pipe carrying the contaminated water. This shockwave then separates the liquid into two streams, selectively pulling certain electrically charged atoms, or ions, toward one side of the flow by tuning the properties of the shockwave to match the target ions while leaving a stream of relatively pure water on the other side. 

The stream containing the concentrated lead ions can then be easily separated using a mechanical barrier in the pipe.

Professor of chemical engineering Martin Bazant said“In principle, this makes the process much cheaper because the electrical energy that you’re putting in to do the separation is going after the high-value target, which is the lead. You’re not wasting a lot of energy removing the sodium.”

“Because the lead is present at such low concentration, there’s not a lot of current involved in removing those ions, so this can be a very cost-effective way.”

“The process still has its limitations, as it has only been demonstrated at small laboratory scale and quite slow flow rates. 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. But it could be practical within a few years for some home-based systems.”

“Direct comparisons of the economics of such a system versus existing methods is difficult, because infiltration systems, for example, the costs are mainly for replacing the filter materials, which quickly clog up and become unusable, whereas in this system the costs are mostly for the ongoing energy input, which is very small. At this point, the shock electrodialysis system has been operated for several weeks, but it’s too soon to estimate the real-world longevity of such a system.”

“I think this is an exciting result because it shows that we really can address this important application” of cleaning the lead from drinking water. For example, he says, there are places now that perform desalination of seawater using reverse osmosis. Still, they have to run this expensive process twice in a row, first to get the salt out and then again to remove the low-level but highly toxic contaminants like lead. This new process might be used instead of the second round of reverse osmosis, at a far lower expenditure of energy.”

The findings are published today in the journal Environmental Science and Technology – Water.

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