Removing arsenic from water: faster, cheaper

Arsenic in drinking water is a problem just about anywhere in the world, particularly in developing parts of Asia. To ensure safer drinking water worldwide, researchers at UW–Madison have developed an adsorbent that can remove arsenic from water faster and more cheaply than current methods.

Most of the tap water we drink comes from aquifers underneath the ground. This ground water carries with it arsenic, one of the many metals and minerals that are released from rocks. Arsenic is a contaminant that, when ingested in moderate concentrations over time, can cause skin disorders, tumors, breathing problems and organ damage. To remove arsenic, ground water is filtered through treatment systems that contain small, porous particles called activated alumina that catch molecules of arsenic as water passes over them.

But, explains Jim Park, a civil and environmental engineering professor, the small pore size and surface area of the activated alumina particles limit the arsenic molecules that the particles can trap.

Developing a more effective and economical method, he says, would enable many water treatment systems, especially those in rural areas, to meet new regulations from the Environmental Protective Agency. The new regulations lowered the limit of arsenic in drinking water from 50 to 10 parts per billion. Meeting this new standard, says Park, will cost treatment plants an estimated $1.5 billion, which could translate into $1,900 increases in annual water bills for some customers.

To help meet the new regulations economically, Park and graduate student Min Jang have developed a particle that more effectively adsorbs arsenic from water as it’s being treated. The particle, made from a mesoporous media developed by Mobil scientists in 1992, could be used anywhere from wells to treatment plants to home-faucet filters. It is patented by the Wisconsin Alumni Research Foundation.

Unlike the particles of activated alumina, Park’s particles are bigger and have larger pores that are all the same size. They’re also coated with metal oxides that react only to arsenic — a quality, he says, that could keep many healthful minerals in the water, but remove other water contaminants, such as phosphorous, nitrate or mercury.

When Park’s group compared the two arsenic adsorption methods — activated alumina and the coated material — they found that the new material could remove twice as much arsenic at a rate 15 times faster, and the cost of manufacturing was 70 percent less.

“Arsenic in drinking water is a worldwide problem, especially in Bangladesh, Pakistan and India … One of the reasons we wanted to develop this more efficient, less expensive method was so many people could benefit,” Park says.