Modelling of cometabolic transformation ofortho-xylene in a denitrifying biofilm system

A model describing the cometabolic biotransformation ofo-xylene with toluene as primary carbon source in a continuously fed fixed biofilm reactor is presented. The model is based on the concept of competitive inhibition betweeno-xylene and toluene. The proposed model simulated successfully the transformation ofo-xylene and the associated by-products formation, as well as the toluene degradation. However, it appears that an accurate measurement of active biomass density and distribution in the biofilm is needed, since these factors dramatically affects the modelling. The modelling of various kinetic experiments indicates that the active biomass (or toluene degraders) is accumulated on the top of the biofilm, leading to the conclusion that only a minor part of the biofilm thickness was active. The calibrated model is able to predict the removal of toluene ando-xylene for concentrations ranging from 0 to 30 mg/L. For higher concentrations toxicity phenomena may decrease the accuracy of the model.