Electron donor and chlorinated ethene effects on activity and community composition\ud in anaerobic reductively dechlorinating consortia

Graduation date: 2009This research focused on anaerobic transformation of trichloroethene (TCE), a\ud groundwater contaminant. The mixed anaerobic Evanite culture (EV) was studied to determine community behavior and composition responses to different electron donors and chloroethene electron acceptors. The potential toxicity from high concentrations of TCE and its daughter product cis-1,2-dichloroethene (cDCE) was also evaluated.\ud Electron donor and acceptor studies were performed in three continuous flow stirred tank reactors (CFSTRs) operated with 12.5 day cell retention times. Each reactor\ud received either TCE or vinyl chloride (VC) and a soluble electron donor at twice the\ud stoichiometric hydrogen formation potential to dechlorinate the influent TCE or VC\ud completely to ethylene (ETH). The EV inoculum for the CFSTRs contained the critical dehalogenating organisms, Dehalococcoides spp., as well as three reductive dehalogenase genes found only in Dehalococcoides and commonly referred to as the pceA, tceA, and vcrA genes. CFSTR assessments consisted of: continual chloroethene and organic acid monitoring; periodic batch rate measurements of TCE, cDCE and VC dechlorination under non-limiting conditions; and quantitative polymerase chain reaction (qPCR) analyses of the aforementioned reductase genes plus the Dehalococcoides 16S rRNA and universal Bacteria 16S rRNA genes.\ud Formate was a better electron donor for TCE dechlorination in terms of completeness and longevity of dechlorination, and in maintaining Dehalococcoides populations. In the VC-fed reactor, formate could not sustain dechlorination, but supported an unknown TCE to cDCE dechlorinating population. The lactate-fed CFSTR produced a Dehalococcoides community dominated by the tceA gene, while the two formate-fed systems were generally dominated by the vcrA gene. Dehalococcoides 16S rRNA gene quantities correlated well with cDCE and VC batch-measured dechlorination rates. cDCE and VC maximum dechlorination rates could be predicted by qPCR Dehalococcoides 16S rRNA gene measurements.\ud High chloroethene concentration toxicity effects were studied using batch-fed reactors, a CFSTR and a recirculating packed column reactor. In all reactor types TCE\ud dechlorination activity was lost as cDCE concentrations reached 9 to 12 mM. A toxicity\ud model, based on cDCE and TCE concentrations directly increasing the endogenous decay\ud coefficients of the cultures, fit the temporal concentration responses observed in all reactors, with slightly different toxicity constants