Biocatalytic conversion of contaminants is a promising new technology for water treatment applications due to the diversity of biological enzymes, their speed and selectivity, and their ability to operate under mild conditions. A model example is removal of the endocrine-disrupter perchlorate. Biocatalytic perchlorate reduction to chloride and oxygen has been demonstrated in groundwater samples and occurs even in the presence of excess nitrate. In the current work, we investigated the potential for a hybrid ion-exchange/biocatalytic perchlorate removal process in which perchlorate is biocatalytically removed from spent ion exchange brines. Perchlorate reduction was measured using methyl viologen as electron donor. Average activities and standard deviations of three independent biological replicates are reported in U(µg Mo)-1, with U defined as µmol of methyl viologen oxidized per minute and normalized to molybdenum content as a surrogate for perchlorate reductase. Soluble protein fractions were tested in buffered NaCl solutions and real spent ion exchange brine. Complete conversion to chloride and oxygen was confirmed using a Clark-type electrode. Average activities ranged from 146.7 ± 21.8 U(µg Mo)-1 for 0% NaCl to 38.8 ± 3.7 U(µg Mo)-1 for 12% NaCl. The biocatalysts were also active in spent ion exchange brine obtained from a full-scale facility, although the rate was slower than in the corresponding NaCl solution (19.7 ± 2.5 U(µg Mo)-1 for spent brine versus 89.4 ± 16.2 U(µg Mo)-1 for 6% NaCl). The slower rate can be accounted for by the presence of nitrate, sulfate, and/or bicarbonate in spent brines, based on additional experiments with synthetic brines. These results demonstrate the potential for biocatalytic treatment of perchlorate-containing spent ion exchange brines. This study illustrates some of the benefits of biocatalytic treatment, including rapid kinetics, enhanced perchlorate selectivity in the presence of excess competing anions, and activity under a broad range of salt concentrations.

Biocatalytic perchlorate reduction in spent ion exchange brine

251st National Meeting (2016)

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