Aqueous bromate (BrO₃^–) removal using FILTRASORB 400 activated carbon: effect of process variables and modeling

Aqueous phase bromate (BrO₃^–) treatment using a commercial granular activated carbon (GAC, FILTRASORB 400) indicated that bromate removal is highly influenced by the operational factors such as pH, initial bromate concentration, contact time and the adsorbent dosage. The effect of pH on bromate treatment indicated higher to significant bromate removal at pH ≤ 4, whereas for pH range 5–9 ~ 50% bromate removal was noted. At pH higher than 9, a significant decrease in the bro-mate removal was noted that was ascribed to changes in the GAC surface speciation. Furthermore, a higher mass-based bromate removal transpired with an increase in the initial bromate concentration that was explained based on higher mass transfer and diffusion. Also, the bromate adsorption experimental data fitted well to the Freundlich adsorption isotherm, indicating a multilayer bromate ions accumulation on the GAC surface. Furthermore, an increasing ‘q_e vs. C_e’ trend also implied a multilayer bromate ions attachment on the GAC surface. Moreover, the kinetics experiments showed that the pseudo-second-order kinetic model better describes the respective GAC-based bromate removal as compared to pseudo-first-order kinetic model. This indirectly indicated that the removal of bromate using granular activated carbon is a more involved process, with both adsorption and reduction causing the noted bromate removal (GAC-BrO₃ ↔ GAC-BrO ↔ GAC-Br). It is suggested that initially the adsorbed BrO₃^– ion is reduced to BrO^– (hypobromite) followed by a further reduction of BrO^– to Br^– (bromide) ion. Additionally, as the surface bound bromate ion is reduced to bromide, it would cause further mass transfer of solution phase bromate ion towards the GAC surface, which is also indirectly supported by the aforementioned Freundlich based multilayer bromate removal trend.