Case Study: Solutions For Removing Arsenic In The Presence Of Competing Ions And High pH
By Kim Walsh, EP Minerals
The Environmental Protection Agency's new arsenic rule 66 FR 6976 went into effect January 2006. This new rule reduced the maximum contaminant level (MCL) of arsenic (As) in drinking water from 50 ppb to 10 ppb. Many of the water systems affected by this rule are small, rural systems. Simple low-cost adsorption technology is ideal for many of these systems, however, adsorption is not selective for just arsenic, other contaminants will also be removed. These ions then compete with the arsenic for adsorption sites on the media and can greatly reduce the media's capacity for arsenic removal. This ultimately drives up treatment costs.
Today's commercially available adsorption media are not all made from the same materials. As such, the media on the market today react differently in the presence of competing ions. It is important to consider the competing ions when selecting the best media for a system. The competing ions that tend to cause the most problems for arsenic adsorption media include silica, vanadium, phosphate, and iron.