Identifier

etd-07082013-120440

Degree

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Document Type

Dissertation

Abstract

Sustainable treatment of chlorinated ethanes and ethenes contaminated groundwater using vertical flow engineered wetland systems were investigated in microcosm and column studies. Experiments on environmental and biogeochemical factors that affect system performance were conducted, and a numerical model involving advection, sorption, and sequential biodegradation was developed to describe the fate and transport of the contaminants of concern in the treatment wetland bed. 1,1-dichloroethane (1,1-DCA) and cis-1,2-dichloroethene (cis-1,2-DCE) were used as the chemicals of interest. The presence of cis-1,2-DCE inhibited dechlorination of 1,1-DCA but cis-1,2-DCE dechlorination was not affected by the presence of 1,1-DCA. Simulation runs showed that the treatment bed sizing was controlled by the 1,1-DCA dechlorination kinetics. Bioaugmentation and biostimulation amendments lead to higher dechlorination rates of both cis-1,2-DCE and 1,1-DCA. Studies conducted with different amounts of peat and sand mixtures to investigate long term effects of organic carbon depletion in engineered wetland systems showed complete biodegradation of 1,1-DCA in all soil mixtures with no significant difference in the rate constants. However, simulation runs showed larger bed size requirement for the lowest amount of peat soil used (5% peat) compared to the other peat soils (25%, 50%, and 100%), and no significant difference in the treatment bed size between the 25%, 50%, and 100% peat soils. Complete biodegradation of cis-1,2-DCE and 1,1-DCA was observed in treatment systems incubated at 10oC, 15oC, and 25oC. However, reduced temperatures resulted in lower dechlorination rates. Maintaining the soil and groundwater pH of an engineered wetland system to near neutral pH by applying alkaline solution was observed to be necessary for biodegradation to occur. The potential for plant assisted remediation of 1,1-DCA through the root system of Scirpus americanus indicated possible plant uptake and enhanced system performance. Microbial analysis of the treatment media using quantitative polymerase chain reaction (qPCR) technique, confirmed the presence of Dehalobacter sp. and Dehalococcoides sp. as well as the functional genes bvcA and tcrA reductase known to mediate the biodegradation of chlorinated ethanes and ethenes to non-toxic end products.

Date

2013

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Pardue, John H.

Share

COinS