Effects of adding inert spheres into the filter bed on the performance of biofilters for gaseous toluene removal

To investigate the effect of adding large size inert materials into natural organic packing media in waste gas treatment, two biofilters, one packed with buckwheat hulls and inert spheres and the other packed with buckwheat hulls only, were used in parallel experiments to treat toluene gas for 305 continuous days. The toluene removal capacities and pressure drops of the two biofilters were compared during the experiments. The physical properties of the filter beds were also investigated by pulse injection technique combined with a mathematical model. In the late phase of the operation with a sufficient supply of nutrients, the biofilter with inert spheres showed a higher toluene removal capacity than the biofilter without inert spheres. This was due to the fact that the biofilter with inert spheres had less bed compaction and a greater increase in specific surface area. The pressure drop of the biofilter with inert spheres was also significantly lower and more stable than that of the biofilter without inert spheres due to its higher bed void fraction. All the experimental results quantitatively showed that adding inert spheres into the filter beds could improve the performance of the biofilter under long-term operation.