Aerobic digestion of starch industry wastewater was carried out in an inverse fluidized bed bioreactor using low-density (870 kg/m ) polypropylene particles. Experiments were carried out at different initial substrate concentrations of 2250, 4475, 6730, and 8910 mg COD/L and for various hydraulic retention times (HRT) of 40, 32, 24, 16, and 8 h. Degradation of organic matter was studied at different organic loading rates (OLR) by varying the HRT and the initial substrate concentration. From the results it was observed that the maximum COD removal of 95.6% occurred at an OLR of 1.35 kg COD/(m ·d) and the minimum of 51.8% at an OLR of 26.73 kg COD/(m ·d). The properties of biomass accumulation on the surface of particles were also studied. It was observed that constant biomass loading was achieved over the entire period of operation.