[Abstract] The gaseous emissions from hardboard mill presses at lumber plants contain both volatile and condensable organic compounds, as well as fine wood and other very small particulate material. Biological emissions control for these compounds present several challenges. The biofiltration media provides support and contact between the gas phase contaminants and active microbial cultures attached as biofilms on the media’s surface. As the transformations in the biofilm and the media during optimal biofiltration operations are not well understood, the main aim of this project was to characterize the biofilm formed on the media during the biofiltration process using Fourier Transform Infrared Spectroscopy (FT-IR) and the FT-IR Microscope, and also examine the results along with the performance data of VOC biofiltration field and pilot scale tests. Some differences in the absorbance spectra were observed in the media and biofilm samples collected from the top and the bottom bed of the biofilters. This work suggests that while FT-IR spectral information can provide some useful insights to biofilm coverages and quality within media sections, more work and measurements will be needed to correlate the information to biofiltration performance and optimization.