Elution of inhibitory metabolites is a key parameter controlling the efficiency of air cleaning bio- and biotrickling filters. To the authors knowledge no studies have yet considered the relationship between specific surface area related elution velocity and physical media characteristics, which constitutes a scientific gap. This study investigates the impact of particle size distribution (considering materials with multiple particle sizes) and irrigation rate on the overall specific surface area related elution velocity distribution in porous granular media. The elution measurements performed in this study are performed at a concurrent airflow of 0.3 m s(-1), water irrigation rates of 1-21 cm h(-1) in materials with particle diameters ranging from 2 to 14 mm to represent media and operation conditions relevant for low flow biotrickling filter design. Specific surface area related elution velocity distribution was closely related to the filter water content, water irrigation rate, media specific surface area and particle size distribution. A predictive model linking the specific surface area related elution velocity distribution to irrigation rate, specific surface area and particle size distribution was developed and predicted the observed specific surface area related elution velocity distributions with a mean error of 9%. (C) 2013 Elsevier B.V. All rights reserved.