Written by Noelina Ashwani Dsouza, Staff Writer

In northeastern Brazil, one of the largest industrial areas faces a daunting challenge: cleaning up a site contaminated with a mix of hazardous chemicals. This site, like many others worldwide, requires innovative strategies due to the complexity of its contamination. The site had contaminants from eight categories: BTEX (i.e., benzene, toluene, ethylbenzene, and xylenes), chlorobenzenes, phenols, nitrotoluenes, anilines, cumenes, isocyanates, and others not in the previous categories.

Among the 26 chemicals found, six were particularly concerning due to their high concentrations: chlorobenzene (CB), 1,2-dichlorobenzene (1,2-DCB), 4-nitrotoluene (4-NT), 2,6-dinitrotoluene (2,6-DNT), 4-isopropylaniline (4-IPA), and 1,2-dichloroethane (1,2-DCA). Other chemicals, such as 2,4-dinitrotoluene (2,4-DNT), 2- and 3-nitrotoluene (NT), and 1,4-dioxane, also posed risks to the environment. A research article, Evaluation of Strategies to Remediate Mixed Wastes in an Industrial Site in Brazil’, found in the journal Groundwater Monitoring and Remediation, gives a detailed overview of this topic.

To tackle this complex problem, researchers evaluated various remediation strategies, including aerobic and anaerobic biodegradation, as well as chemical reduction and oxidation. They found that aerobic biodegradation was effective for CB, 1,2-DCB, 2-NT, 3-NT, and 4-NT, but not for the dinitrotoluene isomers, 1,2-DCA, and 1,4-dioxane. However, under anaerobic conditions, 2,6-DNT, 2,4-DNT, and 4-NT could be reduced to amino-toluenes, which could then be further treated with chemical oxidation and/or aerobic biodegradation.

This study suggests a sequential treatment strategy as the most effective approach, starting with aerobic biodegradation, followed by anaerobic reduction, and then aerobic biodegradation and/or chemical oxidation. This strategy was successful in a continuous flow column experiment using soil from the site. While the complex mixtures of contaminants may slow down the remediation process, it is still feasible to achieve effective cleanup through a combination of bioremediation methods.

Despite the challenges, the researchers remain optimistic about the prospects of cleaning up the contaminated site. By employing innovative and environmentally friendly strategies, they hope to not only restore the site but also set a precedent for tackling similar challenges around the world.