Among the efforts directed at remediating contaminated sites, the use of immobilized microorganisms is an appealing alternative because it offers several advantages over the use of free cells, including protecting cells from the toxic effects of hazardous compounds and increasing their survival and metabolic activity. "Pseudomonas putida" is an ubiquitous bacterium which, either as free cells (i.e. in its planktonic state) or immobilized in Ca-alginate beads, is able to effectively degrade pollutants such as cationic surfactants. In this paper, we propose a simple and fast technique to immobilize "P. putida" cells by entrapment in Ca-alginate matrix, and the use of this system and the free cells to estimate the removal of the surfactant Br-tetradecyltrimethylammonium (TTAB). Measurement of residual TTAB with a simple colorimetric method shows that the compound can be removed both by planktonic and immobilized cells. Taking into account that the TTAB-removal rate is higher with immobilized cells than with free cells, the laboratory practical class aims at demonstrating one of the advantages of using immobilized cells in remediation processes. The class is addressed to undergraduate students of biological sciences, engineering and biotechnology, and it could also be applied to evaluate the removal of other pollutants with immobilized microorganisms.