TERMINAL SETTLING VELOCITY AND BED-EXPANSION CHARACTERISTICS OF BIOFILM-COATED PARTICLES

Fluid dynamic behavior of biofilm-coated particles in ambient water ha s been investigated. New experimental results are presented and compar ed with published data. From experimental measurements of the single p article terminal settling velocity the corresponding drag coefficient was found to be larger (by a factor of 1.6) than that for a smooth, ri gid sphere at the same Reynolds number. A new simple correlation descr ibing this finding is suggested. For multiparticle systems the Richard son-Zaki equation, derived empirically for rigid particles, provided a satisfactory description of biological beds. Of the two numerical par ameters characterizing the expansion law, i.e. the slope n and the ext rapolation to voidage equal one u(i), the first was found to be simila r to that suggested by Richardson and Zaki (1954), whereas u(i) gave r esults smaller than the single-particle terminal settling velocity, in contrast with the mentioned work but in agreement with more recently published behavior. (C) 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 62-70, 1999.