In this study, a general transient biofiltration model, which incorporates general mixing phenomena, oxygen limitation effects, adsorption phenomena and general biodegradation reaction kinetics, is developed. Solutions are presented with and without the assumption of pseudo-steady state for the biofilm leading to approximate and general models, respectively. Solutions of the model are presented and validated with experimental transient data of benzene and toluene. Significant improvement in the model prediction is observed in comparison to earlier simplified models. However, the general model predictions seem to be better and it is superior to the approximate model as it does not require any correlations for film thickness or effectiveness factors. Dynamic analysis of the model is performed and compared with experimental data from the literature. Transient behavior during shut-down and restart-up are also well predicted by the model and the transient period does not seem to be long. Model predictions show that the biofilter is able to withstand extreme practical conditions such as random variations in the inlet concentration and gas flow rate. Theoretical analysis shows that the assumption of excess oxygen availability is not a good one, specially at high inlet concentration levels. Sensitivity studies show that mixing in the gas phase is an important phenomenon which should not be neglected and that some parameters need to be accurately estimated.