Biofiltration for volatile organic compound (VOC) control in waste gas streams is best operated at steady contaminants loading. Variations in contaminant loading are, however, common in real applications. In order to provide long-term stable operation of a biofilter under adverse contaminant feeding conditions, a dual-fixed bed adsorption system involving a two-step cycle, i.e., adsorption and desorption, was proposed in this study. The beds of the adsorption unit were packed with granular activated carbon, and the unit was installed in-series before the biofilter. At transient toluene loadings averaging 46.9, 56.3, and 65.9 g/(m(3) h), a biofilter (total bed volume of 2.72 x 10(-3) m(3)) with pre-cyclic adsorber/desorber unit (total volume of 2.06 x 10(-1) m(3)) successfully reduced the waste gas toluene concentration below 5 mg/m(3), while similar behavior was not achieved by a stand-alone biofilter (total volume of 2.72 x 10(-3) m(3)). The net effect of the two-bed adsorption unit was to attenuate the peaks of toluene concentration, and to make the VOC-laden air stream amenable for biofiltration. It was concluded in this study that the integrated treatment scheme compared to a stand-alone biofilter attained the goal of reliably treating fluctuating toluene loading with high removal efficiency. (c) 2006 Elsevier B.V. All rights reserved.