Air Flow Characteristics in Granular Biofilter Media

Pressure drop (ΔP) as a function of air velocity (V) is a key parameter controlling air cleaning biofilter cost efficiency. At present the V–ΔP relationship in biofilter materials must generally be determined experimentally, as no universal link between the V–ΔP relationship and material physical properties have been established. The objective of this study was, therefore, to investigate the link between the V–ΔP relationship, material particle size distribution, and wetting conditions for a common biofilter medium, Leca. Measurements of V–ΔP was carried out for 36 different Leca particle size fractions with different mean particle diameter (Dm) and particle size range (R) under both dry and wet conditions. Measurements showed that increasing Dm and decreasing R together with wetted conditions in the filter generally resulted in decreasing ΔP for the same V. A set of expressions allowing for accurate estimation of the V–ΔP relationship based on Dm, R. and wetting conditions were established, enabling reliable estimation of filter pressure drop (and operation costs) in Leca and similar granular materials.