Background: Packing materials, which are used in biofiltration systems treating gaseous
volatile organic compounds, are expected to have optimal water content in their actual use. This is because
high volume of water increases the diffusion resistance while low water content decreases microbial
activity. Therefore the thickness of the liquid layer on the packing material needs to be identified
to determine the mass transfer process of target pollutants. However, it cannot be measured directly
due to the complicated surface structure of general packing materials.
Methods: In this study, ideal biofiltration surfaces were prepared artificially by coating a plain membrane
surface with mono-cultured biomass and a known thickness of liquid layer. The sorption velocity
of gaseous toluene was then observed, within a considerable range of liquid thicknesses, on this biomass
surface. The velocity of water vaporization from a porous PVF poly-vinyl formal (PVF) material
was then measured. Finally, the relationship between thickness of liquid surface and the water
content of the PVF material was calculated based on the experimental results and a set of mathematical
models on vaporization.
Results: There is an appropriate range for the thickness of the water layer thickness on the biomass at
the surface of packing material. In one case, this thickness was cited as approximately 0.1–0.2 mm for
gaseous toluene. The PVF material was thought to form such a thick water layer at around 50–60% of
its water content. The water content conditions that affect the formation of the water layer changed
when biomass grew on the surface of the PVF material. The range declined from around 70% for new
material to around 55% for biomass-rich material.
Conclusion: This study quantitatively clarified the reason why there is optimal range of water content
for the packing material of biofiltration; i.e., appropriate liquid layer thickness at the surface of packing
materials is built by a certain range of water content.