ABRASION OF SUSPENDED BIOFILM PELLETS IN AIRLIFT REACTORS - EFFECT OFPARTICLE-SIZE

The detachment of biomass from suspended biofilm pellets in three-phas e internal loop airlift reactors was investigated under non-growth con ditions, and in the presence of bare carrier particles. In the experim ents the size of biofilm pellets and bare carrier particles was varied . Results show that an increase in particle size drastically increases the abrasion rate caused by particle collisions. This increase is lar ger than predicted by conventional collision theory, which accounts fo r changes in collision frequency and collision impact. However, collis ion theory was formulated for neutrally buoyant particles which follow the liquid flow. This condition does not hold for biofilm pellets and carrier particles. The difference might therefore be caused by differ ences in particle responses to flow fluctuations. An empirical relatio nship, including this flow response, was formulated. The collision imp act is also strongly affected by the roughness of a bare carrier parti cle: sharp and edgy particles cause much more damage than smoother one s. (C) 1997 John Wiley & Sons, Inc.