A lab-scale trickle-bed air biofilter (TBAB) was operated to evaluate the removal of methyl ethyl ketone (MEK) from waste gas. Three biomass control strategies were investigated, namely, backwashing and two non-use periods (starvation and stagnant). Five volumetric loading rates from 0.70 to 7.04 kg COD/m(3) day were employed. Backwashing once a week removed the excess biomass and obtained long-term, stable performance over 99% removal efficiency for loading rates less than 5.63 kg COD/m(3) day. The two non-use periods could also sustain 99% removal efficiency and could be employed as another means of biomass control for loading rates up to 3.52 kg COD/m(3) day. The non-use periods did not delay the recovery when the loading rate did not exceed 3.52 kg COD/m(3) day. The pseudo-first-order removal rate constant decreased with increase in volumetric loading rate. The effect of non-use periods on removal rate showed apparent transition from positive to negative with the increase in loading rate. (C) 2004 Elsevier B.V. All rights reserved.