Operating parameters for a gas–liquid–solid fluidised bed bioreactor with a low density biomass support

Abstract

The operating parameters for a gas–liquid–solid fluidised bed bioreactor with a low density (matrix particle density smaller than that of water) biomass support were investigated. In particular, the ratio of bed (settled) volume to bioreactor volume ( V b/ V R) and the air velocity U, for which the largest COD removals from brewery wastewater’s were achieved, were determined for a bioreactor with KMT R (Kaldnes Miljotechnologi AS) particles (made of polypropylene) used as biomass support. Measurements of COD versus time were performed in a semi-continuous mode, that is, the air was continuously supplied to a bioreactor and the wastewater was introduced batch-wise at the beginning of experiments conducted for a set U. It was found that the lowest values of COD at the end of operation and hence the largest COD removals were obtained when a bioreactor was operated at the ratio ( V b/ V R) m =0.50 and the air velocity U m=0.018 m/ s . Therefore, these values of ( V b/ V R) m and U m can be considered as the optimal operating parameters for the bioreactor with KMT R particles when used in treatment of brewery wastewaters. The pH was controlled in the range 6.5–7.0 and the temperature was maintained at 28–30°C. In the treatment of a ‘raw’ (no nutrients were added) wastewater, about 70% COD removal was achieved. In the operation with the wastewaters enriched in the nutrients, approximately a 90% COD removal was attained. The following amounts of the nutrient salts (mg/l): (NH 4) 2SO 4 — 500, KH 2PO 4 — 200, MgCl 2 — 30, NaCl — 30, CaCl 2 — 20 and FeCl 3 — 7 added to wastewater before treatment, were sufficient for biomass growth. It was possible to achieve the steady-state biomass loading in a bioreactor with the KMT R biomass support. 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.