BIOLOGICAL DENITRIFICATION OF SPENT REGENERANT BRINE USING A SEQUENCING BATCH REACTOR

The successful development of a laboratory-scale sequencing batch reactor (SBR) denitrification process to treat and reuse nitrate ion-exchange brine is described. Whereas previous research has focused on the use of a continuous upflow sludge blanket reactor (USBR) to denitrify 0.36 N NaHCO3 or 0.17 N NaCl brine containing up to 700 mg NO3-N l-1, this work examines the feasibility of using an SBR to denitrify 0.5 N NaCl brine containing up to 835 mg NO3-N l-1. The influence of salt concentration on denitrification rate was investigated with artificial brine at concentrations of 0.25 and 0.5 N when methanol was the sole exogenous carbon source. After acclimation, the denitrification rate in 0.5 N NaCl was only 10% lower than in the no-salt control reactor. The effect of mass ratio (R) of methanol to nitrate-nitrogen on denitrification rate and residual TOC in the denitrified SBR effluent was studied in the range of 2.2-3.2. At the optimum methanol-to-nitrate-nitrogen ratio of 2.7, the time for >95% denitrification was 8 h. In one set of runs, actual spent regenerant was reused 15 times; each time it was denitrified in the SBR, filtered and compensated with NaCl before reuse. The research indicates that a denitrifying batch reactor provides simple operation, reliable effluent quality and compatibility with the inherent batch operation of the ion-exchange process.