BIOLOGICAL DENITRIFICATION OF SPENT REGENERANT BRINE USING A SEQUENCING BATCH REACTOR

The successful development of a laboratory-scale sequencing batch reac tor (SBR) denitrification process to treat and reuse nitrate ion-excha nge brine is described. Whereas previous research has focused on the u se 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, t his work examines the feasibility of using an SBR to denitrify 0.5 N N aCl brine containing up to 835 mg NO3-N l-1. The influence of salt con centration on denitrification rate was investigated with artificial br ine at concentrations of 0.25 and 0.5 N when methanol was the sole exo genous 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 denitrific ation rate and residual TOC in the denitrified SBR effluent was studie d 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 o f runs, actual spent regenerant was reused 15 times; each time it was denitrified in the SBR, filtered and compensated with NaCl before reus e. The research indicates that a denitrifying batch reactor provides s imple operation, reliable effluent quality and compatibility with the inherent batch operation of the ion-exchange process.