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Investigation of temperature effects on subsurface attenuation of nitroaromatic compounds

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dc.contributor.authorBezold, Zoe Elizabeth, author
dc.contributor.authorBlotevogel, Jens, advisor
dc.contributor.authorDe Long, Susan, advisor
dc.contributor.authorRonayne, Michael, committee member
dc.date.accessioned2015-08-27T03:57:00Z
dc.date.available2015-08-27T03:57:00Z
dc.date.issued2015
dc.description.abstractInadvertent releases of nitroaromatic compounds (NACs) during the production of dyes, explosives, and pesticides have led to soil and groundwater contamination at a chemical production facility in New Jersey. Elevated carbon dioxide fluxes and depleted ¹⁴C content were observed in the contaminated area compared to a background area, indicating that anthropogenic organic contaminants were degrading under natural site conditions. Recent research at Colorado State University has shown that maintaining soil temperatures ~5°C above natural site conditions substantially increases rates of anaerobic petroleum hydrocarbon degradation. The overarching goal of this research is to determine whether thermal enhancement might increase attenuation rates of NACs under otherwise natural conditions at the contaminated site. Detailed depth-resolved site characterization was performed to elucidate current biogeochemical processes. While nitronaphthalene dominated the nonaqueous phase contamination at concentrations up to 47,500 mg/kg, major aqueous contaminants were the more water-soluble 1,3-dinitrobenzene (up to 216 mg/L), 2,4-dinitrotoluene (up to 163 mg/L), and 1,2-chloronitrobenzene (up to 91 mg/L). Comparison of organic carbon in detected contaminants with total organic carbon revealed that there were no other organic contaminants at relevant concentrations in the contaminated area, indicating that the increased CO₂ fluxes were due to mineralization of NACs under natural conditions. The presence of nitroaniline and chloroaniline throughout the entire depth of the shallow aquifer (~3-24 ft bgs) in aqueous samples suggested partial degradation of NACs through reduction of the nitro group, given there are no upstream sources for the anilines. For nitronaphthalene and nitrated toluenes, no degradations products were detected. Microbial diversity analysis revealed that the contaminated transmissive zone was dominated by Pseudomonas stutzeri, a facultative aerobe that has been shown to degrade a variety of monoaromatic compounds including chloronitrobenzene and chlorobenzene. At abundances of up to 83%, it appears likely that P. stutzeri plays a key role in the biodegradation of NACs at the site. The dominance of a nitrate-reducing microbial species, P. stutzeri, and depleted nitrate concentrations suggested that natural degradation processes at the site are limited by electron acceptor availability. Further degradation and mineralization of aniline intermediates, however, may require aerobic conditions. Thus, the aniline compounds may persist under natural conditions or irreversibly sorb to natural organic matter as long as sorption sites are available. To determine the effect of temperature on biodegradation rates, anaerobic microcosms containing homogenized site soil were held at temperatures between 10-30 °C for 350 days. Concentrations of the minor contaminants toluene, xylene, ethylbenzene, and chlorobenzene were significantly depleted. The extent of their degradation along with generated gas volumes suggested a temperature maximum of stimulation around 18-22 °C. In contrast to field observations, reduced organic intermediates of NAC degradation were not detected. However, a slight increase in ammonia was observed, potentially due to slow degradation of NACs. The inability to recreate field degradation rates may likely be attributed to soil sampling and/or homogenization, eliminating favorable biogeochemical zones for site microorganisms. In summary, degradation of select organic contaminants at the site is occurring under natural anaerobic conditions, and may be stimulated by a slight increase in temperature to ~20 °C. However, complete NAC mineralization will likely require oxygen delivery. As a path forward, an aerobic microcosm study is proposed to assess the potential for biodegradation. A subsequent biosparging pilot test, in which subsurface temperatures can be passively raised using gas-permeable surface insulation, may prove the feasibility of this technology for site remediation. Furthermore, consideration should be given to further analysis of subsurface temperature data to resolve natural rates of contaminant degradation in source zones.
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.identifier.urihttp://hdl.handle.net/10217/166905
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado State University. Libraries
dc.relation.ispartof2000-2019
dc.rightsCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.
dc.titleInvestigation of temperature effects on subsurface attenuation of nitroaromatic compounds
dc.typeText
dcterms.rights.dplaThis Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
thesis.degree.disciplineCivil and Environmental Engineering
thesis.degree.grantorColorado State University
thesis.degree.levelMasters
thesis.degree.nameMaster of Science (M.S.)

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