Perchlorate-removal membrane developed at Delaware U

An innovative membrane, synthesized in a laboratory at the University of Delaware, USA, by Professor CP Huang, is said to offer a breakthrough development in clean technology to remove perchlorate from water.

Announcing the development on 14 November 2011, the university said that it was the first attempt to quickly and easily reduce low-levels of perchlorate to non-toxic chloride by combining electrodialysis and an electrochemical reaction in one system.

Perchlorate is an emerging contaminant known to interfere with the metabolism of the thyroid gland in humans. Toxic even at low levels, on the order of 4 ppb, the US Environmental Protection Agency estimates that perchlorate contamination has affected 15 million people in the US via drinking water.

Valued in laboratory experiments because it does not react with any other chemical species in water, perchlorate is a chemical byproduct of common fireworks, fertilizer, hazard flares and matches, as well as rocket fuel, munitions and propellants used in the defence industry.

“Conventional electrochemical reduction of perchlorate to chloride is very slow, and requires a low pH, high perchlorate concentration and high temperature,” explained Huang, whose work is funded through a US$ 365,000 grant from the National Science Foundation.

“Our method enables the first concentration of perchlorate at low levels – on the order of a few ppm to a few thousand ppm – to be collected and reduced under ambient conditions, specifically a neutral pH, room temperature and pressure.”

Huang and doctoral student Poyen (Kevin) Wang have synthesized the membrane to isolate perchlorate from other major anions, such as bicarbonate, nitrate and sulfate, in water.

“Most anionic electrolytes are negatively charged. When placed under the influence of electricity, they naturally migrate toward the positively charged side of the membrane, but only perchlorate is able to pass through,” said Huang.

The process, called integrated electrodialysis and catalytic electrochemical reduction, enables researchers to collect the perchlorate in high concentrations in the reaction chamber, while other major anions remain on the other side of the membrane partition. The accumulated perchlorate is then reduced to non-toxic chloride with a second low-voltage electrochemical current, known as electrochemical reduction.

Huang’s goal is to see the technology implemented in household units to improve the water quality for general consumers or small scale operations, such as hospitals, schools and offices. As the research team learns how the membrane can be modified and applied to other electrolytes, new discoveries are likely to emerge. Updated 15 November 2011 at 23:57 GMT

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