Dedicated to Mom and Dad, for their love and support ABSTRACT Trichloroethene (TCE), a chlorinated ethene with three chlorine atoms, is not thought to occur naturally in the environment at significant concentrations. However, it has been found in the groundwater and other surface water sites as a result of manufacture, use and disposal of chemicals. Now it has become one of the most common water contaminants. People have paid much attention to the removal of TCE especially after it has been confirmed as a human carcinogen by the U.S. Department of Health and Human Services. The Maximum Contaminant Level (MCL) for TCE (5 micrograms/L) has been strictly regulated in drinking water by the USEPA. In the past several decades, in order to remove TCE and other chlorinated ethenes from water resources, various removal processes have been developed. Among them, biological and reductive processes are more favorable than abiotic and/or oxidative processes when considering the removal outcome and overall cost. Moreover, using biobarriers shows great potential due to its effectiveness, durability and environmental friendliness. For biological TCE removal, KB-1TM culture is a commercialized, reliable culture which can perform complete dechlorination from tetrachloroethene (PCE) to the harmless ethene, and it has both Geobacter and Dehalococcoides (Dhc) dechlorinators. In this research, a column study was done to observe and measure the dechlorinating performance of KB-1TM in simulated lab-scale biobarriers. Four mulch columns were set up to act as biobarriers and KB-1TM culture was inoculated into the columns to carry out the dechlorination. iii Previous research has shown that the presence oxygen or other alternative electron accepters like nitrate and sulfate could limit the performance of the dechlorinators. In previous work it was shown that mulch biobarriers inoculated with KB-1TM could completely dechlorinate 1 mg/L TCE even when influent water was saturated with oxygen. In this research, nitrate and sulfate were pumped into experimental columns to determine the impact on dechlorination ability. Control columns were intended to be identical, but without added nitrate or sulfate in their influents. Gas chromatography (GC) was used to detect methane and dechlorination products at locations along the columns, Polymerase Chain Reactions (PCR) (to detect denitrifiers, dechlorinators and methanogens) and gel electrophoresis were performed on DNA extracted from pore water samples from the columns, and Quantitative-PCR (qPCR) was run to quantify microorganisms of interest (methanogens and KB-1TM Dhc) in the columns. According to the GC results and qPCR reports, the KB-1TM Dhc populations in the experimental columns were smaller than those in the control columns. Moreover, the methane production rates and dechlorination rates in control columns were also lower than the rates in the control columns. Complete dechlorination to ethene was seen in control columns but with poor material balances. The presence of nitrate and sulfate as low as 0.25 mM impacted dechlorination rates and end products. Though cis-DCE was seen in experimental columns after nitrate and sulfate were quartered, neither VC nor ethene was observed - suggesting that although the Geobacter population was activated, the Dhc populations were present but inactive. iv