Yale Chemists Use Seafood Waste to
Remove Arsenic from Ground Water
By Jon Luoma
The Bulletin of the World Health Organization has called it “the largest mass poisoning of a population in history,” an environmental tragedy “beyond the accidents at Bhopal in 1984 and Chernobyl in 1986.”
It’s also a case of the best of intentions gone awry. In the 1970s the United Nations Children’s Fund (UNICEF), the World Bank and the government of Bangladesh began a major push to transform the delivery of water in that country. Rivers, ponds, mudholes and shallow pit wells, often rife with disease organisms, had been a major source of drinking, cooking and irrigation water in many parts of the nation. Children, especially, suffered high death rates from such maladies as chronic diarrhea, dysentery, typhoid and cholera.
Hundreds of thousands of tube wells were drilled in ensuing decades, and a new era of clean water seemed to have arrived. Infant mortality rates indeed plunged by about half. But by the mid-1990s, health experts, puzzled by growing rates of arsenic poisoning in the region, began to connect the geological, chemical and medical dots. It turns out that arsenic is naturally abundant in ground water aquifers under large parts of the Ganges River delta, in both Bangladesh and the neighboring Indian state of West Bengal.
In 2008 UNICEF reported that more than one-fourth of wells tested in Bangladesh had arsenic levels of more than 50 parts per billion, the nation’s drinking water standard. Even that is five times the level allowed in the United States and recommended by the World Health Organization. In some villages, more than 80 percent of wells were contaminated. In July the British medical journal The Lancet confirmed that as many as 77 million people in Bangladesh alone have been exposed to high levels of arsenic, with grave short- and long-term health consequences that range from severe skin lesions to organ cancer and cardiovascular diseases.
Chemists at the Center for Green Chemistry & Green Engineering at Yale think they’re on the trail of a process that could cheaply, effectively and sustainably help address this problem. The approach relies on titanium dioxide, a nontoxic and commonly used industrial compound (it’s found in white paints and sunscreen) that’s already known as a useful agent in arsenic detoxification and removal.
But the novel approach also relies on green engineering. Uniquely, it uses recycled wastes from the seafood industry to help make the treatment process in the field both less expensive and less technologically complex. And, in what would amount to a major breakthrough, it ultimately aims to turn the recovered arsenic itself into a marketable resource, safely secured away from water supplies. “We want to close that loop,” says Julie Zimmerman, assistant professor of green engineering at Yale and acting director of the center.
Arsenic contamination of drinking water has also been a problem in the developed world, including parts of the United States, and an array of technologies to remove it in centralized water treatment plants is well-established. But according to Zimmerman, finding “appropriate technologies for the developing world” has proven challenging because of a host of “economic, social and environmental considerations.”
Indian scientist Dipankar Chakraborti, who conducted pioneering studies on the arsenic problem in his country and Bangladesh, has reported that attempts at filtering contaminated well water with elaborate mechanical filtration systems often fail because they are difficult and expensive to maintain.
“Given (the) huge contamination area,” he asked in a 2004 interview, “how many water treatment plants can you install every year? Can you take these to remote villages? Will your people remain alive that long?”
In a new paper for the journal Water Research, Zimmerman and Sarah Miller, a Yale Ph.D. candidate in environmental engineering, propose a solution that amounts to an end run around some of the more technologically complex approaches to arsenic removal.
It was already well-known that arsenic-tainted water can be treated by adding tiny particles of titanium dioxide. The particles are photo-oxidants that will, if exposed to ultraviolet light, tightly bind molecules of arsenic to their surfaces, simultaneously converting the more-toxic form of the poison, arsenic(III), into less-toxic arsenic(V).
The good news, according to Zimmerman, is that the process “takes something toxic and hard to remove and turns it into something less toxic and easier to remove.” The bad news, at least in the context of the developing world, is that once treated, the cloudy water normally needs to be mechanically pumped through filters to remove the miniscule, contaminated particles, adding expense and complexity and demanding large amounts of energy.
Miller and Zimmerman’s new version of the process instead embeds nanosized particles of titanium dioxide in beads of chitosan, the biopolymer that gives crab, shrimp and other crustacean shells their strength. Rather than particles the size of finely sifted flour, the new process yields nuggets of “about the size of Grape-Nuts,” says Miller.
The much-heavier beads settle at the bottom of a container after the embedded titanium dioxide binds up the poison. “You can literally pour clean drinking water off the top,” says Zimmerman.
So far, the researchers have used simple glass containers to expose the beads to the ultraviolet in ordinary sunlight to prove the concept, but they foresee somewhat larger systems, perhaps long plastic or glass tubes exposed to the sun on a rooftop, to provide more-centralized treatment at a village or neighborhood level.
Miller says she found that it was possible to use chitosan after some trial and error in the lab with other compounds. She discovered that she could dissolve small flakes of chitosan in a weak acid solution and simply stir in the titanium dioxide, leaving a substance that looks like white glue. The new substance is then extruded through a needle into beads and dried.
Part of the advantage of using chitosan as a medium is the sheer abundance of its source and the appeal of transforming this seafood industry waste into a valuable resource. “Go to the shore somewhere, like in Maryland,” says Zimmerman. “You can find piles of it. People will pay to have it hauled away.”
But there’s another sustainability advantage. The titanium dioxide-impregnated chitosan beads are themselves recyclable. After clean water is poured off, the beads can be exposed to a moderately alkaline solution—pH 9 to 10, or about the alkalinity of milk of magnesia. That will release the arsenic back into the solution, leaving uncontaminated beads still impregnated with titanium dioxide, for more arsenic removal.
“We still end up with a classic problem,” admits Zimmerman. “We’ve recovered the arsenic. Now what do we do with it?”
The answer to that question is part of the reason the project has won $230,000 in funding from the National Science Foundation (NSF), according to Bruce Hamilton, who leads the environmental sustainability program at the foundation’s engineering directorate.
He says the NSF was especially impressed that the Yale chemists intend to find safe ways to turn the arsenic itself into a resource, to “get arsenic out of the biosphere and lock it up somewhere in, for example, the technosphere,” says Hamilton, pointing out that sustainability advocates increasingly are looking for such “cradle-to-cradle” approaches.
Arsenic is already used in manufacturing, for instance, to make high-efficiency gallium arsenide microchips and solar photovoltaic cells. (Not that moving a waste into a usable product solves everything. Miller and Zimmerman both point to a growing worldwide “e-waste” problem. Electronics components can be recycled and remaining wastes disposed of securely, but that’s not yet being done consistently. It’s a sustainability problem beyond the scope of their project, but of concern nevertheless.)
Miller acknowledges that finding ways to make the waste arsenic a viable raw material for industry will be a challenge. “We face a big hurdle in turning an effluent into the kind of pristine material industry needs,” she says.
If it works, adds Zimmerman, “It could mean industries getting a feedstock that they need by paying for a clean-water project in the developing world.”