Biological perchlorate reduction in high-salinity solutions

Perchlorate (ClO₄^-) has been detected in numerous ground and surface waters, and has recently been added to the drinking water Candidate Contaminant List in the United States. Perchlorate can be removed from drinking water using ion exchange, but this results in the production of highly saline (7-12%) perchlorate-contaminated brines. Perchlorate-degrading microbial enrichments capable of growth in highly saline water were obtained by screening six salt water environments including marine and lake surface waters, salt marshes, subtidal sediments, and a biofilm/sludge from a seawater filter. Perchlorate reduction was obtained in three of these samples (seawater, saline lake water, and biofilm/sludge) at a salinity of 3%. The salinity range of two of these cultures was extended through serial transfers into media having higher salt concentrations (3-7%). Growth rates were measured over a salinity range of 1-15%. The maximum growth rate measured for the saline lake-water enrichment was 0.060±0.003d^-1 (doubling time of 11.6±0.8d) at a salinity of 5%. Growth rates decreased to 0.037±0.002d^-1 at a salinity of 11%, and no growth was observed at salinities of 13 or 15%. These results demonstrate for the first time that biological perchlorate reduction is possible in solutions having a salinity typical of ion exchange brines.