2022 Volume 2 Pages 120-127
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 SO42- 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.