Combined arsenic and nitrate removal by ion exchange

Abstract

If an MCL < 5 μg/L is adopted for arsenic, then many suppliers will need to treat water specifically to remove it. On‐site ion exchange studies investigated the combined removal of arsenic (V) [As(V)] and nitrate from drinking water in McFarland and Hanford, Calif., and Albuquerque, N.M. Whereas previous ion exchange workers had studied removal of high concentrations of As (> 50 μg/L As) without nitrate present, these studies focused on removing 10–15 μg/L As to achieve a product water with < 2 μg/L As while also maintaining nitrate below its maximum contaminant level. Results of 1‐in.‐ (25‐mm‐) column experiments showed that conventional sulfate‐selective resins were better than special nitrate‐selective resins for combined As(V) and nitrate removal. The conventional resins yielded longer run lengths and leaked less As and nitrate into the product water. Decreasing empty bed contact time from 3.0 to 1.5 min did not greatly alter As leakage into the product water. Particulate iron in the ion exchange feed increased As leakage in the product water. Two commercially available computer programs were reasonably accurate in predicting both As and nitrate run lengths for various influent nitrate and sulfate concentrations. Generally, predicted As and nitrate run lengths were within ±35 percent of those observed experimentally.