MODELING OF THE COMETABOLIC BIODEGRADATION OF TRICHLOROETHYLENE BY TOLUENE OXIDIZING BACTERIA IN A BIOFILM SYSTEM

Because of its intensive use in industry, trichloroethylene (TCE) is o ne of the most widespread contaminants in soil and groundwater. The ae robic biodegradation of TCE depends on the supplement of a primary car bon source, of which toluene appears to be the most efficient/practica ble. For this reason, the cometabolic biodegradation of TCE was invest igated in a continuously fed biofilm reactor with a mixed culture of t oluene degraders. The interaction phenomena between toluene and TCE we re studied and modeled in order to develop a kinetic model for the des ign of treatment processes. TCE degradation ([TCE] = 40-135 mg/L) was dependent upon the presence of toluene; however, if the latter was sup plied at concentrations above 1 mg/L, TCE degradation was strongly inh ibited. Similarly, TCE inhibits toluene degradation ([TCE] < 50 mu g/L ). A simple kinetic model which incorporates competitive inhibition be tween toluene a nd TCE, as well as the activation effect from toluene, was developed. A fair agreement between modeled and experimental data was found. However, the kinetic model was not able to predict the ICE removal in the absence of toluene (resting cells) or at very low tolu ene concentrations (i.e., below 0.1 mg/L). Parameter estimation yielde d a maximum TCE degradation rate, k(x(TCE)), of 0.38 +/- 0.11 gTCE g(x ) day(-1) and a half-saturation constant for TCE, K-S(TCE), of 0.17 +/ - 0.1 mg/L. Furthermore, the model calculations suggested that the act ive biomass (toluene degraders) accumulated at the top of the biofilm in an active layer of ca. 120 mu m. Finally, sensitivity analyses defi ned the model's uncertainties to be +/-30-35% for TCE. The calibrated model is able to predict fairly well the removal of TCE for concentrat ions ranging from 0 to 5 mg/L.