Effectiveness of complex organic electron donors with respect to PCE dechlorination is investigated.

"The primary goal of this research was to determine the ability of a culture taken from a bulk-aerobic fluidized-bed reactor (FBR) to dechlorinate tetrachloroethylene (PCE) under anaerobic conditions when provided with an electron donor and nutrient source. Subsequent objectives examined the effects of toluene, 1,1,1-trichloroethane (TCA), and chloroform (CF) on the dechlorination of PCE."--Abstract.

Soil and groundwater contamination stemming from the release of various chlorinated compounds into the environment is a significant and difficult site remediation challenge. The articles in this collection discuss the use of aerobic and anaerobic biological degradation to dehalogenate sites contaminated with pesticides and chlorinated solvents such as trichloroethylene, tetrachloroethene, tetrachloromethene, perchloroethylene, carbon tetrachloride, pentachlorophenol, and chlorinated benzene. Bench- and field-scale studies of the biological processes associated with in situ dechlorination of soil and aquifers are described. Discussed are the uses of microcosm studies and numerical simulation of dechlorination to manage system operation. Site characteristics (e.g., hydraulic properties, temperature, nitrogen availability) and their effect on the stability of the methanotrophic community are examined. Methods discussed include the use of air venting, alternative electron donors, biofilm reactors, surfactants, municipal digester sludge, iron enhancement, and sulfate reduction to improve conditions for the microbial consortia that effect dechlorination.

This research focuses on the anaerobic transformation of trichloroethylene (TCE) that is occurring in the subsurface of the Evanite site in Corvallis, OR. Two anaerobic studies were conducted to investigate the effects of microbial communities in the presence of different electron donors during the anaerobic degradation of trichlorofluoroethylene (TCFE), and TCE. The first study was conducted in the groundwater microcosm bottles, filled with groundwater collected from the monitoring well 15 at the site. Because TCE was present in low concentrations in this well, TCFE was added to the microcosms as a surrogate compound that might be dehalogenated like TCE. Lactate, formate and hydrogen were evaluated as substrates for driving the anaerobic transformations. These substrates and products are potential electron donors to enhance the dechlorination of TCE and possibly TCFE. When injecting TCFE with one of the substrates in the microcosm bottles, a quick reduction of TCFE was observed to cis-dichlorofluoroethylene (cis-DCFE), and the transformation of the substrates to acetate. When TCFE and TCE were present as mixtures, a faster reduction of TCE to cis-DCE was observed compared to TCFE to cis-DCFE. The second study was an in-situ push-pull test at well15. Formate and TCFE were added to groundwater extracted from well 15. The amended groundwater was injected and extracted after a reaction time ranging from 3 to 5 hours. This study was conducted to determine the in-situ response to the addition of an electron donor to enhance the biotransformation of TCFE and TCE. During the push-pull test no transformation of formate to acetate was observed. Some TCFE was transformed to cis-DCFE. It is possible that another electron donor was present in the aquifer that lead TCE to transform to cis-DCE and furthermore to VC, and TCFE to cis-DCFE under reductive dechlorination conditions. These anaerobic systems involve the interaction of several reactions within the microbial population. Different transformations throughout the experimentation were an indication that the microbial population was active during the different stages of the study.