Firstly, biofilm and biosorbents are defined. Mechanisms of interactions between metal ions and biofilm are discussed in terms of diffusion, mass transfer and sorption. In a second step, different processes using biofilm to remove heavy metal in aqueous solutions are presented. The continuously stirred processes are described for metal ion removal in wastewater by biofilm coating particles. In this case, the equilibrium data obtained with isotherm curves show a good adsorption of several metal ions onto biofilm. Examples of adsorption capacities for a large number of microorganisms and heavy metal ions are presented. The fixed bed reactors packed with grains coated with a biofilm are efficient to get a sorption (adsorption or ion exchange) of cations. The pressure drop is calculated with classical equations. Some values such as adsorption capacities and breakthrough times are got from the breakthrough curves. Several models (Adams-Bohart, mass transfer, and homogeneous surface diffusion models) are applied to get design data. A new approach using neural network to model breakthrough curves is proposed and discussed.