Modeling transport and fate of chlorinated hydrocarbons governed by biotic transformation in porous media

A macroscopic partitioning model governed by microbial transformation was developed to elucidate the transport and fate of chlorinated hydrocarbons and microorganisms in porous media. Carbon tetrachloride (CT) and 1,1,1-trichloroethane (TCA) were selected as the target compounds. A laboratory column experiment was also conducted to validate the accuracy of the model. Results obtained from the TOC concentration and microbial activities in effluent and pore water demonstrate that the steady state of the microbial growth was reached after an incubation period of 40 days. Microorganisms tended to accumulate in the first 20 cm of the column and consumed auxiliary substrate rapidly to sustain the dechlorinating capabilities. Significant degradation of CT with the concomitant increase of chloroform, the daughter product of CT via dechlorination, was also demonstrated after 57 days. TCA is more recalcitrant than CT. Removal of 42% of the original TCA input was demonstrated in 121 days. No 1,1-dichloroethane was detected. Model simulation results indicate that the predicted concentrations are all in the range close to the experimental data. A good correlation between the simulated and measured values demonstrates that the partitioning model can describe the transport and fate of chlorinated hydrocarbons and microorganisms In the contaminated groundwaters. The distribution coefficient between free-living and attached bacteria plays a prominent role in controlling the distribution pattern of microorganisms and the fate Of chlorinated hydrocarbons. In addition, the interaction between the supplemental substrate and the active microorganisms significantly influences the dechlorination of chlorinated hydrocarbons. The valid and accurate transport model provides the basis for the accurate prediction of the transport and fate of chlorinated hydrocarbons as well as the proper selection of a remedial approach to eliminate contaminants in soil environments. (C) 1998 Elsevier Science Ltd. All rights reserved.