Abstract
The treatment of phenolic wastewater was investigated in a gas–liquid–solid fluidised bed bioreactor containing polypropylene particles of density 910 kg m^−3^. Measurements of chemical oxygen demand (COD) versus residence time (t) were performed for various ratios of settled bed volume to bioreactor volume (V~b~/V~R~) and air velocities (u) to determine the values of (V~b~/V~R~) and u for which the largest reduction in COD occurred. Optimal operation, corresponding to the largest COD removal, was attained when the bioreactor was controlled at the ratio (V~b~/V~R~) = 0.55 and an air velocity u = 0.036 m s^−1^. Under these conditions, the value of COD was practically at steady state for times greater than 50 h. At this steady state, only about 50% COD removal was achieved in the treatment of a ‘raw’ wastewater (no mineral salts added), whereas in the operation with wastewater enriched in nutrient salts approximately 90% COD removal was attained. The following amount of mineral salts (mg dm^−3^): (NH~4~)~2~SO~4~—500; KH~2~PO~4~—200; MgCl~2~—30; NaCl—30; CaCl~2~—20; and FeCl~3~—7, when added to wastewater before treatment, was sufficient for biomass growth. The application of low density particles (used as biomass support) in a bioreactor allowed the control of biomass loading in the apparatus. In the cultures conducted after change in (V~b~/V~R~) at a set u, the steady state mass of cells grown on the particles was achieved after approximately 6 days of operation. With change in u at a set (V~b~/V~R~), the new steady state biomass loading occurred after culturing for about 2 days. Phenolic wastewater was successfully treated in a bioreactor. In the operation conducted in a bioreactor optimally controlled at (V~b~/V~R~) = 0.55, u = 0.036 m s^−1^ and t = 50 h, conversions greater than 99% were achieved for all phenolic constituents of the wastewater. Conversions of about 90% were attained for other hydrocarbons. Copyright © 2005 Society of Chemical Industry