Two kinds of packing materials, molecular sieve (MS) and polyurethane foam (PUF), were loaded into two identical biotrickling filters respectively to compare the microbial removal efficiency of waste gas containing toluene by seeding with same bacteria. The affecting parameters of the removal performance, such as gas flow rates, inlet toluene concentrations, periods of starvation, were investigated in detail in biotrickling filters. The results demonstrated that both of the packing materials exhibited high toluene degradation efficiency when the gas flow rates ranged from 100 Lh(-1) to 600 Lh(-1). For MS, the total maximum removal efficiency (RE) of toluene maintained 100% when the gas flow rates increased from 100 Lh(-1) to 200 Lh(-1) accompanied with the decrease of empty bed residence time (EBRT) from 266 s to 133 s. However, as for PUF, merely 97.64% RE was obtained at the gas flow rate of 100 Lh(-1) and the EBRT of 266 s. With further increasing the gas flow rates (to 600 Lh(-1)) and decreasing the EBRTs (to 44 s), both the total REs of toluene for MS and PUF decreased to 70.68% and 63.18%, respectively. When varying the inlet toluene concentrations, the REs for MS are able to maintain nearly 100% at the inlet concentration of 9.19 mg L-1 or below, and with the maximum elimination capacity (EC) of 373.24g m(-3) h(-1) (RE = 100%) at the inlet concentration of 9.19 mg L-1. Contrastively, the maximum EC of PUF was only 119.41 g m(-3) h(-1) (RE = 56.66%) at the inlet concentration of 5.19 mg L-1. As illustrated by different starvation period (2, 10 and 60 days), MS possessed shorter recovery time (9 h for 2 days, 17 h for 10 days and 324 h for 60 days starvation, respectively) than PUF (14 h for 2 days, 24 h for 10 days and 324 h for 60 days starvation, respectively). Based on its higher removal capacity of toluene and shorter recovery time, MS would be a better choice than PUF for packing material used for biotrickling filter. (C) 2008 Elsevier B.V. All rights reserved.