Negatively charged anion resins remove negatively charged ionic contaminants in water. Included in this category of resins are strong base/strong anion (SBA) and weak base/weak anion (WBA) resins. These Anion exchange resin example can be used to remove the contaminants described in this section.
Anion exchange resin example can remove nitrate (NO3-). If the ratio of sulfate to NO3– concentration in the water is high, the resin must be regenerated early to avoid the sulfate anion acting as a regenerant and discharging NO3-. In situations with elevated sulfate concentrations, a selective SBA resin can be used as well.
Anion exchange resin example exist that selectively remove perchlorate (ClO4-). These resins can be single-use and/or regenerable.
In water, arsenic is related to arsenate, As(V) and arsenite, As(III). Only negatively charged arsenate (HAsO42-) anions can be removed using SBA resins. Arsenite (H3AsO3) is normally neutral in aqueous solution. Therefore, pre-oxidation is needed to convert As(III) to As(V) anion. Once this oxidation is complete, the residual must be removed before contacting the SBA resin.
Total organic carbon (TOC) or naturally occurring organic matter can be oxidized by secondary chlorine disinfection and create DBPs, such as THMs and HAAs. These DBPs are suspect carcinogens and regulated by the EPA in drinking water. Municipal treatment plants sometimes remove TOC to limit the formation of DBPs. TOC is typically negatively charged and removed using SBA resin.
Anion exchange resin example can be used to remove uranium, which typically exists as anionic uranyl carbonate/sulfate complexes.