October 23, 2021

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Getting the Lead out - MIT finds a new method for removing lead from drinking water

WTNY staff

WTNY Interview with MIT researchers, Mohammad Alkhadra, and Tian Huanhuan. The transcription below has been edited for clarity and length

Background: In the US, an NRDC study published in May 2021, found that 61 million people were served by drinking water systems that detected lead levels that exceeded the 5 parts per billion, and 7 million people were served by systems that had more lead in them than Flint’s water system.

 In Canada, in 2019, 120 reporters, editors, students, and faculty members did a study and report called Tainted Water. The investigation found that the patchwork of provincial regulations across Canada is not tackling lead aggressively, leaving several cities across the country with levels comparable to or higher than those of Flint, Michigan during that city’s 2015 lead crisis.


WTNY: I have with me on the phone, Mohammed Alkhadra, and Tian Huanhuan, from MIT, they have been doing a study and a test on how to get lead out of water. Could you tell me a little bit about it, how the technology works?

Huanhuan: We are using a new technology called “shock electrodialysis”, which is an electrochemical method we developed ten years ago under the tutelage of professor of chemical engineering, Martin Bazant. 

The main part of the device is a slightly charged porous material sandwiched by two cation exchange membranes. The feed stream goes into the porous material.

When we apply an electrical field, a deionization shock wave propagates in the porous material from the cathode side to the anode side, separating the feed stream into a brine stream and a fresh stream. The process results in a 95 percent reduction of lead from the outgoing fresh stream.


WTNY: Can you tell me about how you generate a shock in the water?

Huanhuan: Basically we use the idea of concentration polarization at over limiting (faster than diffusion) current.

When we apply an electrical field, the anions (positively charged ions) tend to move from the cathode side to the anode side but then get blocked by the cation exchange membranes. Cations (negatively charged ions) can go through the device and need to balance the anion charge.

Therefore, ions accumulate on the anode side and deplete on the cathode side. This is called concentration polarization.

If the concentration on the cathode side membrane drops to zero, the resistance explodes, leading to the so-called diffusion-limiting current, which can occur in traditional electrodialysis.

However, the slightly charged porous media in our shock ED device can provide surface conductance and electroosmosis in addition to the bulk electrolyte conductance. This makes overlimiting current possible and expands the deionization zone from the cathode side far into the porous material, which follows a mathematical shock wave.

WTNY: I have been reading that this discovery came about because of a study some years ago, looking to remove radioactivity out of nuclear power plant/reactor wastewater, is that accurate?

Alkhadra: Yes, we did this work in 2019. The problem we were tackling was how to remove these contaminants in a safe and economical fashion without interfering with reactor operation or having to carry out expensive water replacement operations. To achieve this, we were also using shock electrodialysis. Since our process is scalable, we concluded that it can not only be used to clean reactor cooling systems but also for large-scale applications like removing lead from drinking water.

WTNY: Can you tell me how this (lead removal) technology came to be, how this started, and why lead in water?

Alkhadra: I’m happy to talk about this. 

Essentially, we have been working on this technology called “shock electrodialysis” for about ten years. It originated as a theoretical concept developed in our lab. We have demonstrated a few prototypes since then, to remove simple monovalent salts like sodium and chloride.

So, moving forward, a previous student in our lab, Kameron Conforti, discovered the capability of selective removal of multivalent species. By that I mean the removal of divalent components, which are typically heavy metals, typically divalent or even tri-valent, meaning they have a strong electrical charge. We observed that we can remove those to a greater extent than the monovalent salts that are typically benign.

Some of the most persistent contaminants that are both inorganic and multi-valent are heavy metals, like lead, which is particularly nasty because it is present in small quantities and can be toxic at very low levels. Typically, in drinking water, you would have lead concentrations at 1/1000th that of sodium, so ideally you are looking to develop a method that can remove predominantly the lead and leave behind the sodium.

This way, you are expending less energy to remove just the target contaminant, and two, you don’t need to adjust the parameters or composition of the water after you remove the lead; if you remove all of the electrolytes, you will have to reintroduce many of them back into the water to make it safe for drinking.

WTNY: I’ve been told that distilling the water will leave the lead behind, I’ve also been told that the reverse osmosis process also takes the lead out of the water. Do you see your technology as a competitor to these, or what is the advantage? Can we talk about how this would scale up in a plant?

Alkhadra: if you ask anyone to name a few of the most traditional water purification methods, they will probably think of distillation and in some cases, reverse osmosis, as you mentioned. These are typically most suitable for removing a lot of species from concentrated feeds; this could be seawater desalination, brine desalination, and so forth.

These methods, in particular distillation and RO, do not scale well when the feed becomes dilute, so the energy cost becomes too high compared to a lot of these new electrochemical methods, including shock ED.

It would be more favorable to look at electrochemical systems like ours because the energy cost would be much lower when the feed is as dilute as drinking water is. I’m not trying to suggest you can’t use the other processes to remove lead, you absolutely can, it’s just overkill. It would be like taking a plane to fly from your house to the nearest grocery store, you would never do that, it would be prohibitively expensive.

The same applies to this kind of water purification, you could use RO, if it’s very urgent to remove the lead, however it's not the best method for that application. Some more reasonable competitors to our method would include ion exchange and capacitive de-ionization, emerging methods that may be less familiar to your audience. Ion exchange is not new but has its own limitations. These would be more suitable for removing trace amounts of contaminants, like lead.

WTNY: I am trying to understand, with lead so poisonous and so dangerous, have you had interest from people outside the lab, saying look, this is something we want to get involved with. I would think this would be something that investors in Canada or the United States would be keenly interested in. Can you tell me, how a research product goes from the first findings, to the research team, and to the market for commercial use?

Alkhadra : One reason you would use RO over emerging methods is that the new methods are not scaled up yet, as you have noted, so our focus now is to transform this lab-scale prototype into a full-scale commercial device, to process larger volumes of fluid. We have had interest from industry to help us scale up the system. We have a partnership that is currently being formed with a manufacturing company that is interested in helping us scale up the system.

WTNY: When I look at stats coming out of places like Baltimore, Flint, and Chicago, there is a ready market for this technology. How long do you think it will take to get this technology into some of these water plants?

 Alkhadra: What we have all learned in the last two years is “When there is a will there is a way.”

With the emergence of the pandemic, people put their minds to it and significant funding was spent for a solution in record time in human history; if people really want to end this lead problem now, and it could be financed as extensively, then we could come up with a prototype that would work in the next year or two.

Realistically though, at the rate this industry gets funded, we are looking at producing some sort of commercial prototype in the next two years, if our partnership goes through with the manufacturer, we expect to sell modules to the industry, to the market in the next five to seven years.

That would be our timeline, obviously, which could vary depending on the funding we get.

WTNY: I was looking at the idea of taking radiation out of water. There isn’t anyone that doesn’t know about Fukushima and leaks from the plant into the ocean. Is it fair to say there is a solution for that?

Alkhadra: That’s a great question. There are two kinds of key challenges with water contamination in the nuclear industry: one is this sort of latent challenge or problem that has to do with the nuclear disasters we are familiar with, like Chernobyl and the powerplant meltdowns in Japan in 2011. These are both rare events, but they have devastating effects when they occur.

There needs to be some sort of solution to immediately clean up the wastewater, as well as to contain it, or convert it into a more benign or controllable component. Radioactive uranium is very hard to deal with no matter how hard you try, so ideally there would be methods beyond what we do even, more advanced chemical methods to convert these or harness the energy that's released from the radioactive components in a controlled manner.

The other challenge, the one on which our team has been focusing, is a more persistent challenge, which is to remove radioactive ions that are found in the cooling or processing water of the nuclear reactors. These are being continuously generated in the reactor as it is operated, and they need to be continuously removed. It’s not a result of an accident per se, it’s the natural release of these components in a nuclear plant process.

Current methods that exist for these kinds of separations are, as I mentioned, ion exchange, and what we are offering with shock ED is essentially continuous ion exchange and perhaps even superior separation than ion exchange.

And so for that, we can definitely tackle that problem.

As far as cleaning up massive amounts of wastewater this is not a solved problem by any means, and I think Japan has announced it is releasing this water into the ocean, maybe that already happened, or maybe it is happening this year, but it had major news headlines. That problem is not solved by any means.

WTNY: I appreciate you doing this, our viewers will really like this idea.

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