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 hydro carbons 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 acc uracy of the model. Results obtained from the TOC concentration and mi crobial activities in effluent and pore water demonstrate that the ste ady state of the microbial growth was reached after an incubation peri od 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 co ncomitant increase of chloroform, the daughter product of CT via dechl orination, was also demonstrated after 57 days. TCA is more recalcitra nt than CT. Removal of 42% of the original TCA input was demonstrated in 121 days. No 1,1-dichloroethane was detected. Model simulation resu lts indicate that the predicted concentrations are all in the range cl ose to the experimental data. A good correlation between the simulated and measured values demonstrates that the partitioning model can desc ribe the transport and fate of chlorinated hydrocarbons and microorgan isms In the contaminated groundwaters. The distribution coefficient be tween free-living and attached bacteria plays a prominent role in cont rolling the distribution pattern of microorganisms and the fate Of chl orinated hydrocarbons. In addition, the interaction between the supple mental substrate and the active microorganisms significantly influence s the dechlorination of chlorinated hydrocarbons. The valid and accura te transport model provides the basis for the accurate prediction of t he transport and fate of chlorinated hydrocarbons as well as the prope r selection of a remedial approach to eliminate contaminants in soil e nvironments. (C) 1998 Elsevier Science Ltd. All rights reserved.