An analysis of the local processes occurring in a trickle-bed bioreactor (T
BB) with a first-order bioreaction shows that the identification of the TBB
operating regime requires knowledge of the substrate concentration in the
liquid phase. If the substrate liquid concentration is close to 0, the rate
-controlling step is mass transfer at the gas-liquid interface; when it is
close to the value in equilibrium with the gas phase, the controlling step
is the phenomena occurring in the biofilm. CS2 removal rate data obtained i
n a TBB with a Thiobacilii consortia biofilm are analyzed to obtain the mas
s transfer and kinetic parameters, and to show that the bioreactor operates
in a regime mainly controlled by mass transfer. A TBB model with two exper
imentally determined parameters is developed and used to show how the biore
actor size depends on the rate-limiting step, the absorption factor, the su
bstrate fractional conversion, and on the gas and liquid contact pattern. U
nder certain conditions, the TBB size is independent of the flowing phases'
contact pattern. The model effectively describes substrate gas and liquid
concentration data for mass transfer and biodegradation rate controlled pro
cesses. (C) 1999 John Wiley & Sons, Inc.