Treatment of refinery wastewater in a three-phase fluidised bed bioreactor with a low density biomass support

Abstract

The aerobic treatment of refinery wastewater in a three-phase (gas–liquid–solid) fluidised bed bioreactor with a low density (matrix particle density smaller than that of water) biomass support was studied. In particular, the reduction in COD in the wastewater treated in a bioreactor with KMT ® particles (made of polypropylene) used as biomass support was investigated. Measurements of COD versus mean residence time t were performed for various ratios of bed (settled) volume to bioreactor volume ( V b /V R) and air velocities u. The largest COD removals were achieved when a bioreactor was operated at the ratio ( V b/ V R) m =0.55 and the air velocity u m =0.029 m/s. Therefore, these values of ( V b /V R) m and u m can be considered as the optimal for the bioreactor with KMT ® biomass support when used in treatment of refinery wastewaters. Approximately a 90% COD reduction was achieved when the bioreactor was operated at the ( V b /V R) m and u m . The pH was controlled in the range of 6.5–7.0 and the temperature was maintained at 28–30 °C. The steady-state biomass loading occurred in the bioreactor after culturing for about 2 weeks. Particle–particle and particle–wall collisions sloughed off the excess biomass. Clogging and channelling of the bed were eliminated through the intensive motion of the particles. Stratification of the support media coated with the biomass led to movement of the bioparticles to the base of the bioreactor where concentration of contaminants was the highest. This was desirable since the contaminants could penetrate far into the biofilm and hence, most of the biomass was active.