Biodegradation of Chlorobenzenes and Nitrotoluenes at an Industrial Site in South America

Indiscriminate activities have led to environmental problems worldwide, impacting especially international developing regions. As remediation technologies have advanced, numerous sites have been successfully addressed. Many of the sites that still need attention are those at which complex mixtures of contaminants are present, making the development of clean-up strategies more challenging.\nThe Camaçari industrial site that is the subject of this thesis is located in one of the largest industrial facilities in Brazil. The area is characterized by comingled environmental impacts caused by petrochemical industries. The client owns two properties at the industrial pole: Area N and Area P. Both properties are impacted with volatile organic compounds (VOCs) and semi volatile organic compounds (SVOCs) in the soil and groundwater. Area P is the main subject of this work. The site started operations in 1987 and shut down in 2014.\nThe main objective of this research was to evaluate the interactions among chemicals of concern in Area P during biodegradation under aerobic and anaerobic conditions, as well as potential impact of products from sequential chemical reduction/oxidation of the source zone on biodegradation in downgradient groundwater. The eight target chemicals of concern include chlorobenzene (CB); 1,2-dichlorobenzene (DCB); 4-nitrotoluene (NT), 2,6-dinitrotoluene (DNT); 2,4-DNT; 4-isopropylaniline (IPA); 1,2-dichloroethane (DCA); and 1,4-dioxane. Microcosms with soil and groundwater from Area P were used to assess the effect of pH and nutrients on the biodegradation rates of the parent compounds in microcosms. The potential to treat the source zone with chemical reduction and oxidation was explored. Previously developed aerobic enrichment cultures that grow on CB and 1,2-DCB, plus anaerobic enrichment cultures that use lactate as an electron donor to convert 2,6-DNT and NT to corresponding amines, were used to assess the inhibitory or synergistic effects of mixtures of the co-contaminants, as well as the inhibitory potential of the groundwater subjected to reduction/oxidation. The main outcomes were:\n1) pH adjustment for Area P does not appear to be necessary, while the rate of biodegradation may be modestly improved by addition of nutrients;\n2) No inhibitory effects were observed in the rate or extent of anaerobic biotransformation of 4-NT when 2,4-DNT, 4-IPA and 1,4-dioxane were added as co-contaminants at the site’s high concentrations. Minimal inhibitory effects were observed when 1,2-DCA was added as a co-contaminant. Temporary inhibitory effects on the rate of 4-NT degradation were observed when adding 10% of the chemical oxidation groundwater from Area N;\n3) Inhibitory effects were observed in the rate of aerobic biodegradation of CB and 1,2-DCB when all the target compounds as co-contaminants were present at the site’s highest concentration. Regardless, complete degradation was still achieved;\n4) CB and 1,2-DCB served as a primary substrate for aerobic cometabolism 4-IPA and 2,4-DNT. However, the transformation yields are not sufficient to result in a significant level of 4-IPA and 2,4-DNT cometabolism in situ at Area P;\n5) Chemical reduction successfully reduced 4-NT, 2,6-DNT and 2,4-DNT in stoichiometric and higher doses. Chemical oxidation successfully oxidized 4-IPA and the daughter products of nitro group reduction at stoichiometric and higher doses. 1,4-dioxane, 1,2-DCB and CB were partially removed and the removal increased with dose. No removal of 1,2-DCA was observed even at a dose 10 times higher than stoichiometric. Potentially positive effects of the chemical reduction/oxidation groundwater on downgradient biodegradation of CB was observed; and\n6) When exposed to aerobic conditions, 2,6-DAT was consumed at a slow rate. To be effective, sequential anaerobic/aerobic treatment will require enrichment of microbes that actively grow on 2,6-DAT. Overall, the results indicate that use of chemical treatment of the Area P source zone coupled to downgradient biodegradation of the chemical reduction/oxidation products and residual contaminants is sufficiently viable to warrant additional investigation.

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