This work indicates that in bromide-rich drinking waters in which ozone disinfection is employed, the use of magnetic ion-exchange (MIEX) resin is a more appropriate pretreatment process than alum. MIEX achieves superior TOC and THM precursor removal and reduces bromate production.
This US research investigates the performance of treatment with magnetic ion-exchange (MIEX) resin followed by ozonation in achieving disinfection goals, while controlling formation of bromate and chlorinated disinfection by-product (DBP).
Three water samples were collected from raw water supplies impacted by the San Francisco Bay Delta, to represent the varying levels of bromide and total organic carbon (TOC) that occur throughout the year. A fourth water was prepared by spiking bromide into a portion of one of the samples.
Samples of each water were pretreated with alum or virgin MIEX resin, and the raw and treated waters were subsequently ozonated under semi-batch conditions to assess the impact of treatment on ozone demand, ozone exposure for disinfection (CT), and bromate formation.
Finally, aliquots of raw, coagulated, resin-treated, and ozonated waters were chlorinated in order to measure trihalomethane formation potential (THMFP).
In the waters studied, MIEX resin removed 41–68% of raw water TOC, compared to 12–44% for alum. MIEX resin also reduced the bromide concentration by 20–50%.
The removal of TOC by alum and MIEX resin significantly reduced the ozone demand of all waters studied, resulting in higher dissolved ozone concentrations and CT values for a given amount of ozone transferred into solution.
For a given level of disinfection, the amount of bromate produced by ozonation of MIEX-treated waters was similar to or slightly less than that of raw water, and significantly less than that of alum-treated water.
MIEX resin removed 39–85% of THMFP compared to 16–56% removal by alum. Ozonation reduced THMFP by 35–45% in all cases.
This work indicates that in bromide-rich waters in which ozone disinfection is used, MIEX resin is a more appropriate treatment than alum for the removal of organic carbon. This is because it achieves superior TOC and THM precursor removal and reduces the production of bromate from ozone.
