Kinetics of trichloroethylene cometabolism and toluene biodegradation: Model application to soil batch experiments

Trichloroethylene (TCE) biodegradation in soil under aerobic conditions req uires the presence of another compound, such as toluene, to support growth of microbial populations and enzyme induction. The biodegradation kinetics of TCE and toluene were examined by conducting three groups of experiments in soil: toluene only, toluene combined with low TCE concentrations, and to luene with TCE concentrations similar to or higher than toluene. The biodeg radation of TCE and toluene and their interrelationships were modeled using a combination of several biodegradation functions. In the model, the pollu tants were described as existing in the solid, liquid, and gas phases of so il, with biodegradation occurring only in the liquid phase. The distributio n of the chemicals between the solid and liquid phase was described by a li near sorption isotherm, whereas liquid-vapor partitioning was described by Henry's law. Results from 12 experiments with toluene only could be describ ed by a single set of kinetic parameters. The same set of parameters could describe toluene degradation in 10 experiments where low TCE concentrations were present. From these 10 experiments a set of parameters describing TCE cometabolism induced by toluene also was obtained. The complete set of par ameters was used to describe the biodegradation of both compounds in 15 add itional experiments, where significant TCE toxicity and inhibition effects were expected. Toluene parameters were similar to values reported for pure culture systems. Parameters describing the interaction of TCE with toluene and biomass were different from reported values for pure cultures, suggesti ng that the presence of soil may have affected the cometabolic ability of t he indigenous soil microbial populations.