Divalent Cation Addition (Ca 2+ or Mg 2+ ) Stabilizes Biological Treatment of Perchlorate and Nitrate In Ion-Exchange Spent Brine

Anaerobic cultures capable of reducing both perchlorate and nitrate simultaneously in a 3 or 6% NaCl synthetic media were tested for their ability to remove perchlorate and nitrate in actual ion-exchange brines. The addition of divalent cations (e.g., Mg²⁺ and Ca²⁺), and nolmonovalent ions, in greater than typical concentrations, improved cultures stability and the rate of perchlorate degradation. The optimal condition was when Mg²⁺ was added to brine to achieve a ratio of Mg²⁺ to Na⁺ of 0.11 (mol/mol) in 3 or 5.2% NaCl ion-exchange brine. Under these conditions the inoculum was capable of reducing perchlorate to nondetectable limits at rates up to 120 μg/L · h. In this way the brine can be reused in the perchlorate ion exchange process, thus conserving salt (NaCl), reducing waste brine discharge, and eliminating the reintroduction of the contaminants into the environment.