The influence of particles properties on biofilm structure, reactor performance, and energy consumption for denitrifying fluidized bed bioreactors (DFBBRs) using maxi-blast plastic (MX), multi-blast plastic (MB), natural zeolite (NZ), and lava rock (LR) was investigated. The work showed that the particles with sphericity of 0.9 (MB and NZ) maintained a fluffy protruding biofilm and achieved slightly higher nutrient removal efficiencies as compared to the particles with sphericity of 0.5 (MX and LR) which exhibited a patchy biofilm at low C/N ratio. As a results, lower detachment rate and biomass yields were observed for MB and NZ of 0.12 g VSS/g COD, as compared to 0.19 g VSS/g COD for both the MX and LR. This study showed that increasing the biofilm thickness, though not significantly impacting nutrient removal efficiencies, would decrease the annualized energy costs and therefore reduce the long-term operational cost. Moreover, MB appears to be the superior media. (C) 2012 Elsevier Ltd. All rights reserved.