Removal of benzalkonium chloride from aqueous solutions using living biomass of Chlamydomonas reinhardtii: Kinetics, isotherms, and environmental factors

Abstract This study evaluated the ability of the living biomass of the microalga Chlamydomonas reinhardtii to remove benzalkonium chloride (BAC), a widely used disinfectant and emerging aquatic contaminant, from aqueous solutions. To characterize the removal process, the toxic effect of BAC on the microalga was investigated, along with the kinetics and equilibrium isotherms. An FTIR analysis was performed. The effect of exposing the microalgae to light or keeping them in darkness on their BAC removal capacity was studied. Finally, the effect of pH on the efficiency of the process was also studied. This living biomass effectively removed BAC both in light and in darkness, although removal efficiency was significantly higher in the light when the toxic effect of the BAC was lower, which allowed for the existence of a greater number of viable cells. The highest removal efficiency reached 98.3% when the concentration of BAC was 1 mg L⁻ 1 under light conditions and with an initial biomass concentration of 0.4 g L −1 . The maximum removal capacity obtained from the Langmuir model was 48.40 mg g⁻ 1 at 18 ± 2 °C. The removal process followed pseudo-second order kinetics with a maximum kinetic constant of 0.58 ± 0.13 g mg −1 min −1 . FTIR analysis demonstrated the interaction of BAC with biomass, particularly with carboxyl groups. pH strongly affected removal efficiency, with the best performance observed at pH 10. These findings demonstrate the potential of the living C. reinhardtii biomass as an efficient, low-cost, and environmentally friendly biosorbent for BAC removal.