A solid - liquid - gas, multiphase reactor, called Inverse Fluidized Bed Bioreactor (IFBBR) was used in this study for the treatment of starch industry wastewater of high organic content and acidic nature. Mixed culture obtained from the sludge, taken from starch industry effluent treatment plant, was used as microorganisms. Experiments were carried out in an Inverse fluidized bed bioreactor, after the formation of biofilm on the surface of low-density particles (Density = 870 kg/m3). Degradation was studied by varying the initial bed height i.e., 40, 60, 80 and 100cm and for various gas flow rates for each initial bed height. From the results it was observed that a maximum COD removal of 94.3% and BOD removal of 81% were achieved in this reactor. It occurs when the bed height is 80 cm for the airflow rate 225 LPH. It was also observed that 70% removal of total solids.