INFLUENCE OF BIOMASS ACCUMULATION ON BED EXPANSION CHARACTERISTICS OFA DOWN-FLOW ANAEROBIC FLUIDIZED-BED REACTOR

This article describes the bed expansion characteristics of a down-flo w anaerobic fluidized bed reactor treating a synthetic wastewater. Exp eriments were carried out in a 0.08 m diameter and 1 m length PVC colu mn. The carrier used was ground perlite (an expanded volcanic rock). P articles characteristics were 0.968 mm in diameter, specific density o f 213 kg.m(-3) and U-mf(minimal fluidization velocity): 2.3 m.h(-1). E xperimental data of terminal velocities and bed expansion parameters a t several biofilm thicknesses were compared to different models predic ting the bed expansion of up-flow and downflow fluidized beds. Measure d bed porosities at different liquid superficial velocities for the di fferent biofilm thicknesses were in agreement with the Richardson-Zaki model, when U-t (particle terminal velocity) and n (expansion coeffic ient) were calculated by linear regression of the experimental data. T erminal velocities of particles at different biofilm thicknesses calcu lated from experimental bed expansion data, were found to be much smal ler than those obtained when C-d(drag coefficient) is determined from the standard drag curve (Lapple and Sheperd, 1940) or with others' cor relations (Karamanev and Nikolov, 1992a,b). This difference could be e xplained by the fact that free-rising particles do not obey Newton's l aw for free-settling, as proposed by Karamanev and Nikolov (1992a,b) a nd Karamanev et al, (1996). In the present study, the same free-rising behavior was observed for all particles (densities between 213 and 49 0 kg.m(-3)). (C) 1998 John Wiley & Sons, Inc.