ABSTRACT
Biofilters work by using a porous solid medium to support microorganisms and give them access to the contaminants in the air flow. The media used vary tremendously. Most biofilter media include various proportions of biological residues and inert bulking agents (wood chips, activated carbon, polystyrene beads), supplied with an appropriate bacterial inoculum, pH buffer, and mineral salts. Criteria for a good packing are reviewed. From the time biofilters entered the market in the 1970s, researchers have tried to develop better packing mixtures. The result is that there are probably as many different biofilter media as there are biofilters. Advanced packing materials involve complex blending, sometimes with proprietary agents, whereas other low-tech biofilters are simply packed with soils. Various synthetic packing materials have been tested for biofiltration, mainly at the bench scale. The selection of media is not an endorsement of any specific medium but is intended to aid the reader in understanding the many formulations of biofilter media.
