Cheaper, faster method for removing arsenic from water
Arsenic in drinking water is a problem just about anywhere in the world, particularly in developing parts of Asia. In an effort to ensure safer drinking water worldwide, UW-Madison College of Engineering researchers have developed an adsorbent that can remove arsenic from water at faster rates and lower costs than current methods.
Most of the tap water we drink comes from aquifers underneath the ground. This groundwater carries with it arsenic, just one of the many metals and minerals that are released from rocks. To remove arsenic — a contaminant that, when ingested in moderate concentrations over time, can cause skin disorders, tumors, breathing problems and organ damage — groundwater is filtered through treatment systems that contain small, porous particles called activated alumina. These particles catch molecules of arsenic as water passes over them.
But, according to Jim Park, a civil and environmental engineering professor at UW-Madison, the small pore size and small surface area of the activated alumina particles limit the number of arsenic molecules that the particles can trap.
Developing a more effective and economical method, he says, is necessary to enable many water treatment systems, especially those in rural areas, to meet new Environmental Protective Agency regulations regarding how much arsenic can be in drinking water — the limit was lowered from 50 to 10 parts per billion. Meeting this new standard with the current method, says Park, will cost treatment plants an estimated $1.5 billion, which could translate into $1,900 increases in annual water bills for customers in some areas.
To help treatment plants meet the new regulation in an economical way, Park and UW-Madison 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, usually removed by activated alumina, in the water. By changing the surface chemistry, Park says the material can be used to 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. Park says the cost of manufacturing the material, compared to that of activated alumina, was 70 percent less. "Arsenic in drinking water is a worldwide problem, especially in Bangladesh, Pakistan and India, where people suffer from such contamination," says Park. "One of the reasons we wanted to develop this more efficient, less expensive method was so many people could benefit."