Finding new ways to optimize remediation of contaminated soil
Soil at many Superfund sites contains polycyclic aromatic hydrocarbons (PAHs): byproducts of industrial processes such as oil and gas production or wood preservation with creosote. Some of these PAHs are potent carcinogens. One of the most effective ways to clean up these hazardous chemicals is bioremediation, a process in which contaminated soil is excavated and mixed with water and nutrients in a bioreactor tank to create ideal conditions for the bacteria in the soil to degrade – essentially, devour – the PAHs. But some PAHs are more stubborn than others.
“In the bioreactor, most PAH molecules ‘desorb,’ or detach, from the soil particles they’ve been clinging to, ending up in the water where bacteria can eat them,” explains Alden Adrion, a UNC doctoral student in environmental sciences and engineering. “But some PAHs continue to cling to the soil particles, even after bioremediation. This can be a problem if the remaining contamination level exceeds cleanup goals for a particular site.”
Working in the UNC SRP laboratory of Dr. Michael Aitken, Adrion is searching for ways to detach more of those stubborn PAHs from the soil so the bacteria can degrade them, too. He has used PAH-laden soil from a former manufactured-gas plant in Salisbury, North Carolina to test a variety of surfactants, or detergents, to determine which might be most effective in optimizing the bioremediation process.
In early experiments, Adrion ran the contaminated soil through the bioreactor to remove the most easily remediated PAHs, then put it in smaller flasks with a surfactant (five different surfactants were tested) to determine the success at desorption. Now, he is testing the most promising surfactant to determine the optimal dose and length of treatment. And, because some surfactants – even as they enhance desorption – may either prove toxic to the bacteria or cause the bacteria to form toxic products, Adrion is also collaborating with other SRP colleagues to examine the toxicity of the post-treatment soil at varying dose levels.
“We’re trying to find the lowest doses of surfactant that will achieve success without increasing toxicity,” he says. “If we are successful, this could lead to better, cost-effective bioremediation to meet cleanup goals for contaminated sites.”