Novel membrane helps remove perchlorate from drinking water
9:27 a.m., Nov. 14, 2011--We’ve all gazed, transfixed, as fireworks rained down on the Fourth of July, seemingly right above us. But have you ever wondered about the ash heaped beneath the spent firework launch tube?
The white, powdery residue is perchlorate residue, a chemical byproduct found in common fireworks, fertilizer, hazard flares and matches, as well as rocket fuel, munitions and propellants used in the defense industry.
Valued in laboratory experiments because it does not react with many other chemical species in water, perchlorate is an emerging contaminant that is known to interfere with the metabolism of the thyroid gland in humans. Toxic even at low levels, on the order of four parts per billion (ppb), the U.S. Environmental Protection Agency estimates that perchlorate contamination has affected 15 million people in the United States via drinking water.
An innovative new membrane, synthesized in the laboratory of University of Delaware Prof. C.P. Huang, offers a breakthrough development in clean technology to remove perchlorate from water. It is 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.
“Conventional electrochemical reduction of perchlorate to chloride is very slow, and requires a low pH, high perchlorate concentration and high temperature,” explained Huang, Donald C. Phillips Professor of Civil and Environmental Engineering, whose work is funded through a $365,000 grant from the National Science Foundation (NSF).
“Our method enables the first concentration of perchlorate at low levels –- on the order of a few parts per million (ppm) to a few thousand ppm -- to be collected and reduced under ambient conditions, specifically a neutral pH, room temperature and pressure.”
S. Ismat Shah, a professor with joint appointments in the Department of Materials Science and Engineering and the Department of Physics and Astronomy, is co-principal investigator on the three-year grant.
Made from inexpensive plastic, 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 (IED-CER), 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.
Among the membrane’s advantages is its ability to reveal perchlorate’s presence in water -- a significant benefit that can be deployed outside the laboratory for rapid detection of the electrolyte, which might otherwise remain dispersed at low levels and "fly under the radar" of other mechanisms.
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 will likely emerge.
“If we can reduce perchlorate, which is highly inert, using our IED-CER system, we can reduce many other contaminants such as nitrate, organic compounds and heavy metals as well,” he said.
In the meantime, Huang plans to add valuable data to his study by collecting air samples at Taiwan’s annual Beehive festival, held in Tainan City on the last day of Chinese New Year, through collaborations with Genshu Wang, a professor in the School of Public Health at the National Taiwan University.
According to Huang, millions of fireworks are lit during the festival, setting the stage for potential wide-spread perchlorate exposure over a short amount of time.
“Off-ground fireworks, like those popularly used in Asian culture, are particularly susceptible to dispersing perchlorate. We estimate that the exposure is five times higher than normal for event participants,” remarked Huang.
He hopes to document the increased levels of perchlorate to which festival goers are exposed during the event in order to calculate the potential risk to participants.
Article by Karen B. Roberts
Photos by Evan Krape