Degradation of Xylene by a Biofilm Growing on a Gas-Permeable Membrane

In a laboratory reactor, in which a biofilm was grown on a gas-permeable silicone membrane through which oxygen was supplied, the removal of xylene from the bulk fluid was investigated. A mathematical model, by which aerobic xylene degradation, biofilm growth, transport processes in the gas, biofilm and bulk fluid compartment and pH in the biofilm are described, was developed and used to analyse the effect of various experimental parameters on xylene removal. It was found that a few days after the experiment was started, the biofilm thickness reached an optimal value for which all xylene added to the reactor was microbially degraded and xylene was no longer transferred to the gas phase. Beyond the optimal thickness, biofilm growth led to a decrease of the percentage of the xylene which was degraded. This tendency could partly be compensated by an increase of the hydraulic shear stress, oxygen supply or buffer concentration in the reactor influent. A computer simulation showed that the model was able to adequately reproduce the experimental data and allowed to identify relevant experimental parameters, which can be used to control the microbial removal of volatile organics in membrane-biofilm systems.