Long-term performance of bicarbonate-form anion exchange: Removal of dissolved organic matter and bromide from the St. Johns River, FL, USA

The goal of this research was to evaluate the long-term performance of magnetic ion exchange (MIEX) treatment using bicarbonate as the mobile counter ion (i.e., MIEX-HCO3) and sodium bicarbonate for regeneration. This work is important because there are many unknowns concerning the affinity and regeneration efficiency of bicarbonate-form anion exchange, whereas chloride-form anion exchange (i.e., MIEX-Cl resin) is well-studied. Raw water samples were collected approximately two times per month for one year from a single location on the St. Johns River (SJR), FL, USA. The SJR is characterized by high concentrations of dissolved organic carbon (DOC; 12–26 mg C/L) and bromide (550–1100 μg/L), and is being considered as an alternative drinking water supply. Jar tests were conducted using MIEX-HCO3 resin, and MIEX-Cl resin was used as a baseline for comparison. The same batch of MIEX-HCO3 and MIEX-Cl resin was used for the entire study, which was accomplished by regenerating the resins after each jar test in concentrated solutions of sodium bicarbonate and sodium chloride, respectively, and resulted in 21 regeneration cycles. Maximum removal efficiency was achieved with fresh MIEX-HCO3 resin and virgin MIEX-Cl resin. Both forms of fresh/virgin MIEX resin also had the same affinity sequence with sulfate ≈ UV-absorbing substance > DOC > bromide. The removal efficiency of both forms of MIEX resin decreased as the number of regeneration cycles increased, with MIEX-HCO3 resin showing 7–18% lower removals than MIEX-Cl resin after 21 regeneration cycles. The affinity sequence of regenerated MIEX-HCO3 and MIEX-Cl resins differed from fresh resin with UV-absorbing substances > DOC > sulfate > bromide. Scanning electron microscopy and simulated MIEX-HCO3 treatment under rapidly changing water quality were also used to improve the understanding of bicarbonate-form anion exchange. The major contribution of this research is a systematic study of the extended use of bicarbonate-form anion exchange resin in the context of affinity, regeneration efficiency, and changing water quality.

► Bicarbonate-form anion exchange was studied over multiple regeneration cycles. ► Anion exchange was used to treat river water high in organic matter and bromide. ► Bicarbonate- and chloride-form resins performed similarly. ► Removal was UV-absorbing substances > dissolved organic carbon > sulfate > bromide. ► Rapidly changing water quality resulted in release of anions from the resin.