The contamination of wastewater with metals and the use of biotechnologies to remove them is commonly discussed in theoretical biology, microbiology and biotechnology classes aimed at undergraduate students. This work introduces an easy, economical and safe practical laboratory class related to this topic. The practice consists in performing batch assays to remove Al(III) from aqueous solutions by using non-viable bacterial biomass trapped in agar-agar beads. Students prepare these beads and analyse Al(III) adsorption on the basis of: pH, time of contact, and Al(III) concentration. Free Al(III) is quantified spectrophotometrically through a simple colorimetric method. The data obtained are used to calculate and graphically represent the amount of metal adsorbed to the beads. Finally, students analyse and discuss the results to determine the optimal adsorption conditions. Moreover, since Al(III) becomes much more attached to beads with trapped biomass than to beads without microorganisms, the class serves to demonstrate one of the advantages of using immobilised microbial cells in adsorption processes. This class was satisfactorily implemented in an upper-level course for undergraduate students of biological sciences. They were able to properly execute all the experiments and calculations proposed and to become acquainted with useful experimental design to remove a metal.