Degradation of phenol and benzoic acid in a three-phase fluidized-bed reactor

Degradation of phenol and benzoic acid was studied in a fluidized-bed react or (liquid volume 2.17 L) under nonsterile conditions with special emphasis on maximizing the flow through the reactor and investigating reactor perfo rmance at fluctuating feeds. Reactor response to substrate pulses was inves tigated by applying substrate square-wave inputs at a liquid flow of 1.00 L h(-1). A twofold increase of the phenol and benzoic acid feed concentratio ns for 2.5 h did not lead to accumulation and breakthrough. The cells were able to survive four to fivefold increases of the feed concentration for 1 h without loss of viability, although the phenol pulse lead to phenol accum ulation in the reactor. Reactor performance at constantly fluctuating loads was investigated by varying the feed concentrations using sine wave functi ons. No accumulation of phenol or benzoic acid was observed. Influence of i nduction was studied using shift experiments. After 35 days of operation (3 69 hydrodynamic residence times) with phenol as sole substrate (carbon sour ce) the reactor was able to mineralize benzoic acid without any adaptation or lag phase. The capability of phenol degradation, on the other hand, was lost by most cells after only 3 days operation with benzoic acid as the sol e substrate. The experiments underline the importance of induction. In orde r to maximize the flow through the reactor, the liquid flow was increased s tep-wise while the feed concentrations were reduced correspondingly, keepin g the volumetric conversion rates of phenol (0.24 g L-1 h(-1)) and benzoic acid (0.17 g L-1 h(-1)) constant. By this means, liquid flow could be incre ased up to 13.32 L h(-1), which was more than 20-fold higher than the maxim um liquid flow achievable in a chemostat using the same conditions. (C) 200 0 John Wiley & Sons, Inc.