This paper describes the application of two new mathematical models, derived from an existing model with two adjustable parameters, to simulate the breakthrough curves of metal biosorption in fixed bed columns. No new adjustable parameters are introduced into the modified models. The models offer a fast and accurate alternative to the conventional mass balance-based models which are much more complicated mathematically. The major characteristic of this empirical modeling approach is that it requires experimental breakthrough data for model calibration. Modeling results suggest that the new models are capable of describing symmetric and asymmetric experimental breakthrough curves selected from the biosorption literature. Compared to the original model, the modified models show significant improvements for modeling breakthrough curves obtained with columns packed with native biomass but yield only small improvements on deviations from breakthrough data obtained with a column packed with immobilized biomass. (C) 2003 Published by Elsevier B.V.