Evaluation of a pilot plant for removal of nitrate from groundwater using ion exchange and recycled regenerant

A combined system of ion exchange (IX) and advanced biophysical treatment of a recirculating regenerant was tested for nitrate removal from groundwater with minimal brine discharge and chloride addition to the product water. Using well water containing 21.5 ± 1.4 mg NO₃⁻-N/L, optimal IX operation was found at a service cycle of 500 bed volumes (BV). Product water nitrate concentrations (7.4 ± 1.4 mg/L as N) met regulations while minimizing both Cl⁻ addition to the treated water (1.03 meq Cl⁻ added per meq NO₃⁻-N removed) and waste brine production (0.2% of the water volume treated). The total organic carbon in the product water was slightly higher (1.5 ± 0.5 vs. 1.3 ± 0.4 mg/L) than the well water and before disinfection the bacterial count was 10–700 cfu/ml. Brine used to regenerate the IX columns was treated first in a sequential batch reactor (SBR) for biological denitrification followed by ozonation for polishing. The SBR was operated at 8 hour cycles and achieved complete nitrate removal. An ozone dose of 3 to 5 mg/L brine allowed for efficient recycling of the denitrified regenerant by removing suspended solids by foam fractionation. In spite of the low brine blow-down, DOC in the recycled regenerant brine after a year of continuous operation was maintained at relatively low levels of 61.0 ± 11.6 mg/L.