Synthesis of nitrate selective anion exchange resin and denitrification of nitrate adsorbed on the resin

Abstract

To purify groundwater contaminated with nitrate (NO₃-N) from manure and fertilizer used in tea fields, six anion exchange resins made with trimethylamine (1), triethylamine (2), tributylamine (3), trihexylamine (4), trioctylamine (5), or tridecylamine (6) were synthesized, and their performance was evaluated. The NO₃-N removal rates of resins 1–4 were very similar and were higher than those of resins 5 and 6. The nitrate adsorption by all resins was satisfactorily described by the Langmuir adsorption isotherm model. The groundwater originating from tea fields contains high concentrations of SO₄^2- in addition to NO₃-N. Resin 4 had the highest selectivity for NO₃-N adsorption in solutions containing SO₄²⁻. Therefore, resin 4 was selected for denitrification experiments, which demonstrated that NO₃-N adsorbed on resin 4 was denitrified and that resin 4 may be reusable. Biological denitrification was confirmed by measuring nitrous oxide (N₂O) in the headspace of the vial bottle containing 20 mL of the soil solution with NO₃-N removed, 0.1 g of glucose, and 0.1 g of NO₃-N-saturated resin 4. The denitrifying nitrogen calculated from the N₂O concentration was only 0.04% of the NO₃-N adsorbed on the NO₃-N-saturated resin 4. Moreover, when 1 g or more of glucose was added, approximately 10% of the NO₃-N in 10 mL of NO₃-N solution (100 mg-N/L) was absorbed on 0.05 g of resin 4 after denitrification. Further improvements in the efficiency of denitrification are necessary for their application in tea fields.