Biofiltration systems utilizing thermophilic (55 degrees C) bacteria were constructed and tested for the removal of methanol and alpha-pinene--two important volatile organic compounds (VOCs) in the forest products industry. Thermophilic bacterial mixtures that can degrade both methanol and alpha-pinene were obtained via enrichment techniques. Two bench-scale thermophilic biofiltration systems (1085 and 1824 cm3) were used to examine compound removals at different residence times, with influent concentrations of 110 ppmv methanol and 15 ppmv alpha-pinene. At a residence time of 10.85 min, the smaller system had removal efficiencies of >98% for methanol, but only 23% for alpha-pinene. The larger system was operated with the same parameters to evaluate residence time and surfactant effects on compound removals. At a residence time of 18.24 min, both methanol and alpha-pinene removal rates were > or = 95%. However, a-pinene removal dropped to 26% at a residence time of 6.08 min; methanol removal was not affected. Subsequent addition of a surfactant mixture increased a-pinene removal to 94% at the shortest residence time. No residual alpha-pinene was detected with the support medium Celite R-635, indicating that the surfactant may increase mass transfer of alpha-pinene.