Six test runs were carried out to explore the interaction of shear stress and Fe/Mn oxides concentration on the growth of heterotrophic micro-organisms in biofilms. Experimental results revealed that the existence of Fe/Mn colloids was beneficial to biofilm formation. Significant interactions existed (p < 0.001) between shear stress and influent Fe/Mn concentration on biofilm bacteria growth and dissolved organic carbon consumption. Biofilm bacteria numbers were positively related to the dissolved organic carbon consumption rate. This implies that the influent Fe/Mn concentration did not interfere with the uptake of the carbon source by biofilm bacteria. At a higher Fe/Mn concentration (HCS), the biofilm HPC number significantly increased with an increase in shear stress. However, the opposite relation was found at a lower Fe/Mn concentration (LCS). A significant interaction existed between influent colloidal Fe/Mn concentration and shear stress on the kinetic and yield parameters specific growth rate (μ
b
), specific substrate utilization rate (q), and observed growth yield (γ
obs). The size distribution of particles based on particle concentration (No · ml−1) was also examined in the study.
