Determination of the optimal operational parameters for a three-phase fluidised bed bioreactor with a light biomass support when used in treatment of phenolic wastewaters

Abstract

The operational parameters, namely: the ratio of bed (settled) volume to bioreactor volume ( V b/ V R), the air velocity u and residence time t, for which the largest COD removals from phenolic wastewater were achieved, were determined for a three-phase (gas–liquid–solid) fluidised bed bioreactor with KMT ® (Kaldnes Miljotechnologi AS) particles (made of polypropylene) used as biomass support. It was found that the largest COD removals were obtained when a bioreactor was operated at the ratio ( V b/ V R)=0.55, the air velocity u=0.041 m/s and residence time t=45 h . Therefore, these values of ( V b/ V R), u and t can be considered as the optimal operational parameters for the bioreactor with KMT ® particles when used in treatment of phenolic wastewaters. A decrease in COD from 53,400 to 950 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 bioreactor depended on the ratio ( V b/ V R) and the air velocity u. In the cultures conducted after change in ( V b/ V R) at a set u, the constant mass of cells grown on the support media was achieved after approximately a 6-day operation. With change in u at a set ( V b/ V R), the new steady-state biomass loading occurred after the culturing for about 3 days.