Evaluation of Strategies to Remediate Mixed Wastes at an Industrial Site in Brazil

Abstract

Complex mixtures of contaminants at hazardous waste sites often pose significant challenges for remediation. For example, within the largest industrial area in northeastern Brazil, one of the sites is contaminated with at least 26 chemicals, six of which are present in the part per million range: 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 of concern include 2,4-dinitrotoluene (2,4-DNT), 2- and 3-nitrotoluene (NT), and 1,4-dioxane. The objective of this study was to evaluate remediation strategies that include aerobic and anaerobic biodegradation, along with chemical reduction and oxidation. In microcosms prepared with site soil and groundwater, aerobic biodegradation of CB, 1,2-DCB, 2-NT, 3-NT, and 4-NT was demonstrated, while the dinitrotoluene isomers, 1,2-DCA, and 1,4-dioxane were recalcitrant. 2,6-DNT, 2,4-DNT, and 4-NT were readily reduced to amino-toluenes under anaerobic conditions by microbes with lactate serving as the electron donor or using zero valent iron. Amino-toluenes were amenable to chemical oxidation and/or aerobic biodegradation. This suggests a sequential treatment strategy may be the most effective remediation approach, consisting of aerobic biodegradation, followed by anaerobic reduction (abiotic or biotic) and then aerobic biodegradation and/or chemical oxidation. This approach was the most effective in a continuous flow column experiment using site soil. Batch tests with mixtures of contaminants as well as groundwater exposed to chemical oxidation revealed modest to no inhibitory effects. While these mixtures may slow the rate of biodegradation, a remediation strategy that incorporates aerobic and anaerobic biodegradation is achievable.