Breakdown mechanisms and flow characteristics involved in an immobilized M. rouxii biomass bed treating oil-in-water emulsion were investigated. The purpose of this research was to evaluate the applicability of the well-known Carman-Kozeny filtration equation to a 1000 mm immobilized M. rouxii biomass bed treating a standard mineral oil-in-water emulsion at six different flow rates (12, 16, 20, 24, 28, and 32 mL/min). The specific permeability coefficient, the Carman-Kozeny constant, and the shape factor of immobilized M. rouxii bed were found to be 2.135 x 10(-8) m(2), 5.03, and 1.13, respectively. The coalescence efficiency decreased with an increase in bed depth (from 15.9% at 200 mm to 4.0% at 1000 mm depth for a flow rate of 12 mL/min). Results indicated possible sequential occurrence of coalescence and filtration in the immobilized M. rouxii biomass bed.