Detachment of biomass from suspended nongrowing spherical biofilms in airlift reactors

Abstract

In three-phase internal loop airlift reactors, the detachment of biomass from suspended biofilm pellets in the presence of bare carrier particles was investigated under nongrowth conditions. The detachment rate was dominated by collisions between bare carrier particles and biofilm pellets. The concentration of bare carrier particles and the carrier roughness strongly influenced the detachment rate. A change in flow regime from bubbling to slug flow considerably increased the detachment rate. Otherwise, the superficial gas velocity did not directly affect the detachment rate. The influence of particle size was not clear. The bottom clearance did not affect the detachment rate within the tested range. Other aspects of reactor geometry might be important. The main detachment processes were abrasion and breakage of biofilm pellets. During the detachment process, two phases could be distinguished. In the first phase the detachment was relatively high, and both breakage and abrasion of biofilm pellets occurred. During the second phase, breakage dominated and the detachment rate was lower. The two-phase behavior is explained by differences in strength between the inner and outer biofilm layers, possibly caused by variations in local growth rates during biofilm formation. Differences in growth history might also explain the various detachment rates observed with different biofilm batches. (c) 1995 John Wiley & Sons, Inc.

Adhesion and biofilm development on suspended carriers in airlift reactors: Hydrodynamic conditions versus surface characteristics

“…To discriminate and quantify the effects of shear stress, turbulence, the presence of air bubbles, and particle collisions, further experiments are necessary. These are described elsewhere (Gjaltema et al, 1995(Gjaltema et al, , 1996. In general, the role of detachment in biofilm formation seems to deserve more attention.…”

Effect of scale-up on average shear rates for aerated non-Newtonian liquids in external loop airlift reactors

“…The determination of average shear rate in bioreactors is an important step in deciding their suitability to handle shearsensitive biosystems. High shear fields resulting from the fluid physical properties and the hydrodynamics may cause damage to fragile microorganisms and biofilms formation (Duddridge et al, 1982;Gjaltema et al, 1995Gjaltema et al, , 1997Kieran, 1993;Lau and Liu, 1993), or mechanical instability to immobilized biocatalysts (Leenen et al, 1996;Martins dos Santos et al, 1997). Average shear rate is also needed for correlating hydrodynamics and mass and heat transfer data in non-Newtonian systems.…”

Hydrodynamic characteristics and gas–liquid mass transfer in a biofilm airlift suspension reactor

“…The reactor has been described by Gjaltema et al (1995), and the essential details are given in Figure 1. The temperature of the reactor was maintained at 24°C by means of a…”