Removing Arsenic from Water: Improving the Process

Environment Canada scientists have developed a new way to remove arsenic from water, using a process that is both cost-efficient and easily portable.

Their work provides hope to communities in countries such as Sri Lanka and Bangladesh, where arsenic in drinking water causes "blackfoot disease." Sufferers of this condition have to have their limbs amputated.

The scientists, working in partnership with Canada's ZENON Environmental Inc., were able to use extremely small particles of alumina, a form of aluminum oxide that is a white powder. Arsenic-laden water is fed into a tank reactor, where the molecules of arsenic are held in the surface and pores of the alumina through a process called adsorption, in much the same way that water is held in a sponge. The water/alumina mixture then moves to a membrane unit for microfiltration. Water travels through the membrane, but the particles, and the arsenic, are rejected, and are returned to the tank so the alumina can be reused.

The process was originally developed to remove arsenic from mining effluents and wastewater, but can also be used to make drinking water safe. It has been shown to be effective at removing 99.99 per cent of the arsenic from mining effluence with a concentration of 100 parts per million (ppm) of arsenic. The technology is most effective, however, at removing arsenic in concentrations of 4-5 ppm, or 4,000-5,000 parts per billion (ppb). In comparison, the acceptable level of arsenic for discharge is 50 ppb, and for drinking water, 25 ppb.

The process is also self-regenerating. When sufficient quantities of arsenic and alumina have been rejected by the membrane, an alkaline solution is added to the reactor that causes the arsenic to separate, or de-absorb, from the alumina. The mixture then travels to the membrane again, and the concentrated arsenic flows through, while the rejected alumina is regenerated and reused.

The apparatus used to carry out this process is small and self-contained, and can be transported on a trailer. This makes it particularly effective for developing countries, where arsenic poses a hazard to drinking water. Areas of Canada and the United States also must deal with this problem. In Canada, naturally ocurring arsenic is found in rocks in Nova Scotia, and leaches into water. In the United States, some remote communities in New Mexico and Arizona have to bring in drinking water by truck because of arsenic in the local water.

Previous methods of removing arsenic used larger particles of alumina, and this slowed down the adsorption time. Environment Canada scientists and their partners have patented their discovery in both Canada and the United States, and are currently examining whether the technology can be adapted to remove lead and selenium from water.

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