Identifier

etd-0124103-165322

Degree

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Document Type

Dissertation

Abstract

Bench-scale continuous vertical flow column and microcosm studies were conducted to investigate the attenuation potential of chlorinated volatile organic compounds (CVOCs) in constructed wetland soil mixtures prepared from peat, compost and sand and in a pristine natural freshwater wetland soil. The study also determined geotechnical properties of potential synthetic peat mixtures for construction of treatment wetlands for CVOCs. Trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE) and 1,2-dichloroethane (1,2-DCA) were the main test chemicals used during the studies. Based on geotechnical and sorption characteristics, two mixtures (one comprised of sand and peat and the other comprised of sand, peat and compost product) were selected out of ten potential soil mixtures for column and sorption studies as the most promising materials for construction of the wetland. Faster removal kinetics and higher sorption potential were observed in peat/compost/sand mixture than in peat/sand mixture for all pollutants tested. Degradation kinetics of cis-1,2-DCE and 1,2-DCA were observed to be fastest under methanogenesis followed by sulfate-and sulfite-reducing conditions. Detection of the 16S rDNA gene of Dehalococcoides sp. via DNA extraction, PCR amplification, cloning and sequencing was directly correlated with complete dechlorination of TCE and cis-1,2-DCE to ethene. Two steady-state solute transport models were used to model TCE attenuation in natural and constructed wetland mesocosms, one equation had a dispersion term whereas another equation ignored the dispersion effects. Both models were able to capture the spatial concentration trends of TCE in the soil columns equally well. However, the model without the dispersion term underestimated the TCE removal rate constant by a factor of at least two compared with the other model. TCE attenuation rate constants were observed to be significantly faster in the constructed wetland columns than in the natural wetland columns. Model simulations indicated that attenuation of TCE in the constructed wetland columns was controlled by biodegradation whereas both sorption and biodegradation were equally important removal mechanisms in the natural wetland columns. The results of this study may be useful in establishing design information for treatment wetlands for CVOCs.

Date

2003

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

John H. Pardue

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