Investigation of perfluorooctanoic acid and perfluorooctane sulfonate adsorption by Ca- and Fe-modified biochars: Potential of Ca-modified biochar in real water matrices

Abstract

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are persistent organic pollutants widely found in water matrices and pose significant ecological and health risks. This study investigated the adsorption behaviors and mechanisms of calcium- and iron-modified biochars (CMB and IMB) fabricated from mandarin peel and focused on their applicability in real water matrices. CMB and IMB exhibited markedly enhanced adsorption capacity compared to unmodified biochar (MB), contributed to improved electrostatic attraction and ion and ligand exchange across a broad pH range. In real water matrices, IMB demonstrated superior efficiency in simpler matrices like tap water, while CMB showed better performance in more complex environments such as river water and sewage treatment effluent. These results were attributed to the competitive adsorption of PFOA and PFOS onto IMB in the presence of coexisting ions and humic acids compared to CMB. A quadratic regression model successfully predicted adsorption capacities under various water conditions, supporting its effective use in real water matrices. This study highlighted the potential of modifying CMB and IMB for the removal of PFOA and PFOS by demonstrating their effectiveness in complex or simple water matrices and further emphasized that Ca-modified biochar is particularly promising under more complex water environmental conditions.