Comparison of toluene removability and pressure drop in biofilters with four types of packing materials

Abstract

Selection of suitable packing materials is one of key factors in biofilter performance and sustainability for the control of malodorous organic gases because the properties of packing materials have a high influence on them. To select the best available packing material for malodorous organic gases such as toluene and benzene, biofilter performance was compared in biofilters employed different packing materials including porous ceramic (celite), Jeju scoria (lava), a mixture of granular activated carbon (GAC) and celite (GAC/celite), and cubic polyurethane foam (PU). A toluene-degrading bacterium, Stenotrophomonas maltophilia T3-c, was used as the inoculum. The high toluene elimination efficiency over 95% by each four biofilter was maintained for 15 to 20 days. In the other three biofilters, the elimination efficiency was significantly decreased as extending operation period, but it was maintained steady for 30 days in the PU biofilter. The maximum elimination capacities in the celite, lava, and GAC/celite biofilter were 100, 130, and 110 g m-3 h-1, respectively. However, the elimination capacity for the PU biofilter was approximately 360 g m-3 h-1 at an inlet loading of approximately 430 g m-3 h-1, which was 2 to 3.5 times higher than for the other biofilters. The pressure drop gradually increased in the GAC/celite, celite and lava biofilters after 23 day due to bacterial over-growth, and the toluene removal efficiency remarkably decreased with increasing pressure drop. During the subsequent period, the biofilm growth created increasing resistance to gas flow through the porous bed because the void space available for convection was gradually reduced. Clogging caused the appearance of a black color in the biofilter due to anaerobic degradation of the biomass. This occurred not only in the celite biofilter but also in the lava and GAC/celite biofilters. Backwashing method was not effective for the control of biomass in these biofilters. In the PU biofilter, however, backwashing allowed maintenance of a pressure drop of 1 to 3 mm H2O m-1 and a removal efficiency of > 80%, indicating that the PU was the best packing material for toluene removal among the packing materials tested.