The application of laccase and manganese-dependant peroxidase (MnP) from Trametes versicolor to facilitate removal of aromatic hydrocarbons from a petrochemical industrial effluent was investigated. The enzymes were immobilised onto polysulphone ultrafiltration membranes thus facilitating enzyme-substrate contact and the activity and duration of activity was determined with respect to the enzymatic degradation of the aromatics within the effluent. The phenomenon of fouling typically associated with the operation of ultrafiltration systems was reduced by the action of the immobilised enzyme layer. To determine the different 'defouling' potential of MnP NaF and NaN3 were applied to the system as inhibitors of laccase. Differing 'defouling' efficiencies were then compared with standard inhibition kinetics associated with the non-immobilised enzyme suites. The system was also applied to an industrial petrochemical-based effluent and compared with the synthetic make-up effluent in terms of 'defouling' efficiency. The presence of high concentrations of fluoride at the membrane interface during the ultrafiltration of the petrochemical-based effluent contributed significantly to the inhibition of the immobilised enzyme suite and thus manifested as a significant decrease in 'defouling' potential in comparison with the system being operated using the synthetic make-up effluent.