Selective removal of bromide and iodide from natural waters using a novel AgCl-SPAC composite at environmentally relevant conditions

The removal of bromide (Br⁻) and iodide (I⁻) from source waters mitigates the formation of brominated and iodinated disinfection by-products (DBPs), which are more toxic than their chlorinated analogues. In this study, we report on our recently developed environmental-friendly method for the preparation of novel silver chloride/superfine activated carbon composite (AgCl-SPAC) to rapidly and selectively remove Br⁻ and I⁻ from surface waters. The material characteristics were tracked, before and after treatment, using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS) spectroscopies. The results showed very fast removal kinetics of Br⁻ and I⁻ by AgCl-SPAC with equilibrium times at 150 s and <10 s, respectively (i.e., 2–3 orders of magnitudes faster than previously tested Ag-based composites). In addition, AgCl-SPAC was evaluated under eight different Cl⁻ concentrations up to 400 mg/L and exhibited high removal efficiencies for I⁻ (i.e., >90% at all tested conditions) and Br⁻ (i.e, >80% at Cl⁻ = 0.5–200 mg/L, and 60–75% at extreme Cl⁻ conditions = 300–400 mg/L). Unlike previous Ag-based composites, AgCl-SPAC performance was not affected by elevated concentrations of two types of natural organic matter (2–16 mg-NOM/L). The superior performance was further confirmed in four different surface waters and one groundwater. After the removal of Br⁻ and I⁻ from all waters by AgCl-SPAC, the subsequent DBPs formation (trihalomethanes, haloacetic acids, and haloacetonitriles), total organic halogens (TOX), bromine substitution factor (BSF), and calculated cytotoxicity under the uniform formation conditions (UFC) decreased significantly. Overall, this novel composite represents a promising alternative approach, to be integrated continuously or seasonally, for controlling the formation of brominated and/or iodinated DBPs at water treatment plants.