Biological wastewater treatment in the inverse fluidised bed reactor

Abstract

Abstract The biological wastewater treatment was investigated in the inverse fluidised bed reactor (IFBR) in which polypropylene particles of density 910 kg/m 3 were fluidised by an upward flow of gas. Measurements of chemical oxygen demand (COD) versus residence time t were performed for various ratios of settled bed volume to reactor volume ( V b / V R ) and air velocities u g . The largest COD removal was attained when the reactor was operated at the ratio ( V b / V R ) m = 0.55 and an air velocity u gm = 0.024 m/s. Under these conditions, the value of COD was practically at steady state for times greater than 30 h. Thus, these values of ( V b / V R ) m , u gm and t can be considered as the optimal operating parameters for a reactor when used in treatment of industrial wastewaters. A decrease in COD from 36,650 to 1950 mg/l, i.e. a 95% COD reduction, was achieved when the reactor was optimally controlled at ( V b / V R ) m = 0.55, u gm = 0.024 m/s and t = 30 h. The pH was controlled in the range 6.5–7.0 and the temperature was maintained at 28–30 °C. The biomass loading was successfully controlled in an IFBR with support particles whose matrix particle density was smaller than that of liquid. The steady-state biomass loading depended on the ratio ( V b / V R ) and an air velocity u g . In the culture conducted after switching from the batch to the continuous operation, the steady-state biomass loading was attained after approximately 2-week operation. In the cultures conducted after change in ( V b / V R ) at a set u g , the steady-state mass of cells grown on the particles was achieved after about 6-day operation. For a set ratio ( V b / V R ), the biomass loading depended on u g . With change in u g at a set ( V b / V R ), the new steady-state biomass loading occurred after the culturing for about 2 days.