AbstractA laboratory‐scale trickle bed air biofilter (TBAB) packed with synthetic, inorganic media for microbial attachment was used for toluene removal from an air stream. Three experimental strategies—including backwashing as the active biomass control and two non‐use periods (starvation, which represents a period without toluene loading, and stagnant, which reflects no flow)—were considered in this study. The non‐use periods can be considered as another means of biomass control for low VOC loadings (0.70 and 1.41 kg COD/m3·day), whereas at high VOC loading (>3.52 kg COD/m3·day) backwashing is deemed essential to remove the excess biomass accumulation in the biofilter. As the toluene loading rate was increased, a considerably longer reacclimation period was unavoidable for biofilter performance to reach the 99% removal for all experimental strategies (backwashing, starvation, and stagnant). Because the biofilter response was strongly dependent on the active biomass in the system, biofilter response after the non‐use periods was significantly different from that after backwashing. © 2005 American Institute of Chemical Engineers Environ Prog, 2005