AWWA ACE63178

Ion exchange (IX) resins can reduce nitrate concentrations in groundwater to very low levels; however, regeneration brines containing high nitrate concentrations pose a disposal problem. This research investigated hydrogenotrophic (hydrogen utilizing) biological reduction of nitrate in regenerant brines. Salt tolerant denitrifying batch cultures were enriched from the denitrification stage of a wastewater treatment plant and marine sediments from Cape Cod, Massachusetts and the Dead Sea. The cultures were inoculated into nitrate nutrient media, with and without added NaCl, with hydrogen as the sole electron donor. The salt tolerant cultures were able to denitrify 800 mg/L NO₃-N in the presence of 12.6 g/L NaCl to 200 mg/L NO₃-N. The cultures were inoculated into two different hollow fiber membrane bioreactors (HFMBs), one fed 50 mg/L NO₃-N with no added NaCl (non-brine) and the other fed 600 mg/L NO₃-N with 12.5 g/L NaCl (brine). The non-brine HFMB was able to consistently reduce nitrate to less than 8 mg/L at a hydraulic residence time (HRT) of 5 hours when pH and biofouling were controlled. The brine HFMB only achieved partial denitrification at an HRT of 53 hours. Current research is focused on treatment of the brine in a batch HFMB. Includes 11 references, figures.