THE EFFECT OF LIQUID-PHASE ON VOC REMOVAL IN TRICKLE-BED BIOFILTERS

The objective of this work was to analyze the effect of water content on the removal of volatile organic compounds (VOCs) in gas phase trick le-bed biofilters. Previous studies revealed that excessive accumulati on of biomass in the reactor had a negative effect on contaminant remo val efficiency. To solve this problem, periodic backwash was used to r emove excess biomass and maintain an effective operation Results showe d that the ether removal efficiency dropped immediately after backwash ing and gradually improved to reach the optimal value within about 24 hours. The initial drop in performance can be attributed to biological effects, such as loss of active biomass and the necessity for an adap tation period for the microbial culture. However, mass transfer limita tions due to the water retained in the reactor may also be important. To investigate the effect of water content on the biofilter performanc e, an experiment evaluated the effect of draining after backwashing wa s conducted. Biofilters were allowed to drain for different periods of time before restarting the reactors. A longer lapse time in draining before the restart resulted in better ether removal efficiency. The im provement of biofilter performance after backwashing was explained wit h a combination of biological and physical effects. A mathematical mod el was then used to simulate the performance of the biofilter under th ese conditions and to support the conclusions obtained. The mathematic al model considered a three-phase system (biofilm, water, and gas phas e), dynamic processes, non-uniform bacterial population, and one limit ing substrate. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.