Removal of bromide from water by adsorption on silver-loaded porous carbon spheres to prevent bromate formation

Abstract

Bromate is a potential toxin that can be formed from bromide during the disinfection of drinking water by ozone. The performance of silver-loaded porous carbon spheres (SLPCSs) for removing the bromate precursor, bromide (Br−), was investigated under a range of conditions. The saturated SLPCS were then regenerated and tested to determine reusability. Porous carbon spheres (PCSs) were also prepared by carbonization of spherical poly(vinylidene chloride) and their ability to remove bromide compared with SLPCS. SLPCS were more efficient adsorbents than PCS because of the presence of silver and their adsorption capacity reached as high as 1.20mg/g at 25°C under the experimental conditions used. The removal of Br− by SLPCS was determined by batch and rapid small-scale column tests to assess the kinetic and dynamic adsorption behaviors. The equilibrium adsorption data fit well with the Langmuir isotherm and the Br− adsorption process followed a pseudo-second-order kinetic model. Both removal efficiency and adsorption capacity improved with increasing temperature. The feasible range of pH for Br− removal was between 4 and 7 and optimal performance was attained at pH 5. The presence of competitive species, such as Cl−, I−, NO3-, SO42- and humic acid, resulted in poor Br− adsorption, with their impact following the order: I−>SO42->NO3->Cl−. In the presence of competitive species, the impact of pH was minor, except for the I− anion. Regenerated SLPCS retained satisfactory performance.