Date of Award
12-2024
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Environmental Engineering and Earth Science
Committee Chair/Advisor
Kevin Finneran
Committee Member
Diana Vanegas
Committee Member
Ronald Falta
Abstract
Industrial sites contaminated with a complex matrix of chemicals represent a problem for the ecosystem and a high risk for the health of all individuals. That is why remediation strategies are needed to mitigate this environmental impact. The latex zone, located at the Corteva industrial site in San Lorenzo, Argentina, is the subject of this research. The environmental impacts in this area are a consequence of petrochemical operations carried out for many years.
Monoaromatic hydrocarbons such as styrene, ethylbenzene, and benzene, and chlorinated methanes like carbon tetrachloride, chloroform, dichloromethane, and chloromethane are among the contaminants identified at the site that stand out due to their elevated concentrations and regulatory limits. Any remediation strategy, whether an active degradation technique or natural attenuation, requires a detailed study of the inhibitory or synergistic interactions between the mixture of contaminants present at the site.
The main objective of this research was to develop a microbial-chemical strategy for styrene, ethylbenzene, benzene, and carbon tetrachloride degradation. The experimental approach was to develop an enrichment culture that aerobically biodegrades styrene, ethylbenzene, and benzene by testing two different sources of inoculum: a leachate from a landfill and a gasoline contaminated sediment from the shores of Lake Hartwell. Then, with the preparation of resting cell suspensions in batch incubations, characterize the enriched microbial consortium by analyzing the effect that different factors like oxygen availability, temperature, substrate addition and pH can have on styrene aerobic biodegradation and determine the inhibitory or synergistic effect of bi-mixtures and all contaminants mixed on styrene aerobic biodegradation. Three additional batch experiments consisted of the evaluation of styrene degradation through chemical oxidation with the utilization of potassium permanganate as an oxidant agent, a bioaugmentation preliminary experiment to test if the enriched microbial culture adapts to an aquifer's actual conditions and can degrade styrene, and a pilot study to analyze the possible reductive dechlorination of carbon tetrachloride mediated by the action of dissimilatory Fe(III)-reducing indigenous bacteria present in surrogate aquifer materials.
Based on the results, the main outcomes were:
Aerobic biodegradation of styrene, benzene and ethylbenzene was demonstrated in batch incubations using the mixed microbial consortium dominated by Streptomyces sp., enriched from a gasoline-contaminated sediment on the shores of Lake Hartwell in Clemson, SC.
Potassium permanganate in stoichiometric dose was effective in the chemical oxidation of styrene at a high concentration.
No significant difference was observed between applying pure oxygen and air saturation conditions on the microbial activity toward styrene degradation. Anoxic conditions inhibited microbial activity.
The microbial activity of the culture was temperature independent. The bacteria were able to degrade styrene at similar rates at all temperatures tested (4°C, 18°C, 25°C, and 37°C).
The mixed microbial consortium's capacity to degrade styrene was inhibited by concentrations of styrene exceeding 162 mg/L.
The microbial activity was significantly inhibited in both acidic (pH 5) and alkaline (pH 9) conditions.
The microbes partially degraded both styrene and ethylbenzene, although ethylbenzene was significantly more degraded during 66 hours of incubation. On the other hand, styrene biodegradation outcompeted benzene biodegradation. Carbon tetrachloride and chloroform considerably slowed down but did not inhibit the microbial activity toward styrene degradation. Although the styrene biodegradation slowed down, the presence of all contaminants mixed had no inhibitory effect on the microbial activity.
The bacteria were incapable of styrene degradation when bioaugmented to the surrogate aquifer.
The different treatments applied for the biostimulation of native Fe (III)-reducing bacteria were unsuccessful. No Fe (III)-reducing activity was observed; therefore, dechlorination of carbon tetrachloride was not detected in the batch incubations monitored for one month.
Recommended Citation
Flórez-García, Marcela C., "Microbial-Chemical Degradation of Styrene in Co-mingled Plumes With Ethylbenzene, Benzene, and Carbon Tetrachloride" (2024). All Theses. 4444.
https://open.clemson.edu/all_theses/4444