Aerobic treatment of wastewaters in the inverse fluidised bed biofilm reactor

The aerobic treatment of wastewaters was investigated in the inverse fluidised bed biofilm reactor (IFBBR) in which polypropylene particles of density 910 kg/m3 were fluidised by an upward cocurrent flow of gas and liquid. Measurements of chemical oxygen demand (COD) versus residence time t were performed for various ratios of settled bed volume to bioreactor volume (Vb/VR) and air velocities u to determine the optimal operating parameters for a reactor, that is, the values of (Vb/VR), u and t for which the largest reduction in COD occurred.The largest COD removal was attained when the reactor was controlled at the ratio (Vb/VR) = 0.55 and an air velocity u = 0.021 m/s. Under these conditions, the value of COD was practically at steady state for times greater than 25 h. In the wastewater treatment conducted in a reactor optimally controlled at (Vb/VR) = 0.55, u = 0.021 m/s and t = 25 h, a decrease in COD from 27,650 to 450 mg/l was obtained, that is, approximately a 98% COD reduction was achieved. The pH was controlled in the range 6.5–7.0 and the temperature was maintained at 28–30 °C.The biomass loading in a reactor depended on the ratio (Vb/VR) and an air velocity u. In the cultures cultivated after change in (Vb/VR) at a set u, the steady-state mass of cells grown on the particles was achieved after approximately 3 days of operation. With change in u at a set (Vb/VR), the new steady-state biomass loading occurred after cultivation for about 2 days.