AN ECOLOGICAL RISK ASSESSMENT FOR A SOUTH AFRICAN ACID MINE DRAINAGE

A dynamic model that describes the biodegradation of secondary substrates through oxygenase reactions in biofilms has been developed. The model incorporates intracellular reducing power, in the form of NADH, as a link between the rate of utilization of primary substrates and the biodegradation of secondary substrates. The reaction kinetics were integrated into a diffusive biofilm model with internal and external mass transfer limitations and then combined into a continuous flow reactor model. Preliminary evaluation of the model has demonstrated that mass transfer limitations substantively reduced the removal of the secondary substrate as compared to a suspended growth reactor with an equivalent mass of biomass. A sensitivity analysis revealed that model predictions of the removal of secondary substrate were highly sensitive to the parameters describing the availability of reducing power and to the compound-specific biodegradation kinetic parameters.