Numerical simulation of transport and sequential biodegradation of chlorinated aliphatic hydrocarbons using CHAIN_2D

Microbiological degradation of perchloroethylene (PCE) under anaerobic cond itions follows a series of chain reactions, in which, sequentially, trichlo roethylene (TCE), cis-dichloroethylene (c-DCE), vinylchloride (VC) and ethe ne are generated. First-order degradation rate constants, partitioning coef ficients and mass exchange rates for PCE, TCE, c-DCE and VC were compiled f rom the literature. The parameters were used in a case study of pump-and-tr eat remediation of a PCE-contaminated site near Tilburg, The Netherlands. T ransport, non-equilibrium sorption and biodegradation chain processes at th e site:were simulated using the CHAIN 2D code-without further calibration. The modelled PCE compared reasonably well with observed PCE concentrations in the pumped water. We also performed a scenario analysis by applying seve ral increased reductive dechlorination rates, reflecting different degradat ion conditions (e.g, addition of yeast extract and citrate). The scenario a nalysis predicted considerably higher concentrations: of the degradation pr oducts as a result of enhanced reductive dechlorination of PCE. The predict ed levels of the very toxic compound VC were now an order of magnitude abov e the maximum permissible concentration levels, Copyright (C) 1999 John Wil ey & Sons, Ltd.