Modelling biooxidation of iron in packed-bed reactor

A model based on Monod kinetics and originally developed for use with rotating biological contactors was modified for use with a packed-bed column reactor. The reactor was filled with expanded polystyrene beads to immobilize chemolithotrophic bacteria and fed up to 570 mg L-1 (similar to 10 mM) ferrous iron [Fe(II)] in simulated acid mine drainage. A tracer study indicated changing behavior as a function of hydraulic residence time (HRT), with a transition from complete mix flow behavior to plug flow behavior as HRT decreased. The Fe(II) oxidation efficiency exceeded 95% until the HRT was reduced below 0.5 h. The reactor performance could be predicted with the model using estimates from the literature for (u) over cap and Y. The experimentally determined half-saturation constant K-s was found to range from 5 to 12 mg L-1. The maximum volumetric capacity constant R-max was estimated to be similar to 360 mg Fe(II)h(-1) L-1 beads under complete mix flow conditions but appeared to be as high as 724 mg Fe(II)h(-1) L-1 beads as conditions approached plug flow at short HRTs.