Enhanced Removal of Polystyrene Microplastics in Drinking Water Treatment Using Iron-Modified Activated Carbon

Abstract Granular activated-carbon adsorption is operationally simple and compatible with water-treatment systems, while iron modification may introduce additional interaction sites. However, its benefit for removing polystyrene (PS) microplastics under different pH conditions and water matrices remains unclear. This study compared commercial coconut-shell-derived activated carbon (CBT) and its iron-modified counterpart (CBT-Fe) for removing nominally 500 nm PS particles from deionized water at pH 4.0 and 7.0. At pH 4.0 and 2.5 g L–1, CBT-Fe achieved 93.06% removal and an equilibrium capacity of 2.94 mg g–1, compared with 20.56% and 0.63 mg g–1 for CBT. CBT-Fe reached equilibrium after 16 h, versus 30 h for CBT. At pH 7.0, equilibrium capacities were comparable, although CBT-Fe equilibrated faster. In PS-spiked municipal tap water, CBT-Fe retained measurable removal over five consecutive loading cycles without regeneration. These findings demonstrate a condition-dependent benefit of iron modification and support further evaluation in water treatment.