BIOFILM ABRASION BY PARTICLE COLLISIONS IN AIRLIFT REACTORS

Biofilm development is determined by the balance between growth and de tachment. The detachment of biomass from suspended biofilm pellets was investigated in three-phase internal loop airlift reactors under non- growth conditions, and in the presence of bare carrier particles. Part icle collisions were found to dominate the detachment. These collision s caused an on-going abrasion of the biofilm pellets. The abrasion rat e was linear with both the concentration of biofilm pellets and the ba re carrier particles up to a solids hold-up of 30%. An increase in par ticle size drastically increased the abrasion rate. Carrier roughness also strongly influenced the detachment rate. Experimental results wer e interpreted in terms of collision frequency and collision impact, an d could partly be described by conventional collision theory. Particle responses to flow fluctuations, the effect of carrier roughness and t he effect of growth rate on biofilm strength and elasticity need to be included. Some consequences for reactor operation and start-up are di scussed. (C) 1997 IAWQ. Published by Elsevier Science Ltd.