Characterization of tetrachloroethene-dechlorinating bacteria and investigation into their ability to enhance removal rates of tetrachloroethene-containing nonaqueous phase liquids
Carr, Cynthia Schmidt
Hughes, Joseph B.
Doctor of Philosophy
The influence of electron donors on the ability to sustain tetrachloroethene (PCE) dechlorination was investigated in recycle columns containing a PCE-dechlorinating mixed culture. Over a period exceeding one year, it was demonstrated that equivalent amounts of lactate, methanol, and hydrogen could sustain rate and extent of dechlorination equally. Dechlorination was not impacted by competition for electron donor at high hydrogen partial pressures, despite the presence of an actively methanogenic community. Results from these experiments imply that cost and method of delivery may dictate electron donor selection for stimulation of anaerobic in situ dechlorination. Efforts to isolate PCE-dechlorinating organisms from the mixed culture resulted in the development of a highly purified co-culture that dechlorinated PCE to cis-dichloroethene and was dominated by curved, motile rods and cocci. Preliminary molecular biology techniques were employed to characterize the ecology of the purified culture. It was discovered that multiple microorganisms, one of which shared 98% 16S rDNA sequence identity with the fermentative coccus, Lactosphaera pasteurii, were present. Experiments characterizing the nutritional requirements of the purified coculture determined dechlorination sustainment required the addition of filter-sterilized cell extract prepared from the parent mixed culture. It was determined that hydrogen, pyruvate, glucose, ethanol, and yeast extract could sustain dechlorination, while formate, acetate, acetaldehyde, lactate, propionate, butyrate, and methanol could not. Experiments to determine the effect of dechlorination on the longevity and composition of PCE-containing NAPLs were conducted in continuous-flow stirred-tank reactors (CFSTRs). Comparisons between biotic and abiotic CFSTRs demonstrated that dechlorination resulted in a factor of 14 increase in PCE removal rates from the NAPL. Dechlorination daughter products partitioned between the aqueous and NAPL phases, resulting in temporal changes in NAPL composition. The combined effects of dissolution and dechlorination on the removal of chlorinated ethenes from the NAPL were described using a mathematical model that approximated dechlorination as a pseudo first-order process. It was determined that total chlorinated ethenes removal from the NAPL would be achieved in 13 days in the biotic CFSTRs, as compared to 77 days in the abiotic CFSTRs---corresponding to an 83% reduction in the longevity of the chlorinated ethenes component of the NAPL.
Microbiology; Environmental science; Environmental engineering