The effect of liquid phase on VOC removal in trickle-bed biofilters

Abstract

The objective of this work was to analyze the effect of water content on the removal of volatile organic compounds (VOCs) in gas phase trickle-bed biofilters. Previous studies revealed that excessive accumulation of biomass in the reactor had a negative effect on contaminant removal efficiency. To solve this problem, periodic backwash was used to remove excess biomass and maintain an effective operation. Results showed that the ether removal efficiency dropped immediately after backwashing 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 adaptation period for the microbial culture. However, mass transfer limitations due to the water retained in the reactor may also be important. To investigate the effect of water content on the biofilter performance, an experiment evaluated the effect of draining after backwashing was 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 improvement of biofilter performance after backwashing was explained with a combination of biological and physical effects. A mathematical model was then used to simulate the performance of the biofilter under these conditions and to support the conclusions obtained. The mathematical model considered a three-phase system (biofilm, water, and gas phase), dunamic processes, non-uniform bacterial population, and one limiting substrate.