Evaluation of the Efficiency of Modified Zeolite in Nitrate Removal from Agricultural Drainage Water Using Fixed Bed Columns

Nitrate is one of the worldwide pollutants of groundwater and surface water, which affects human and livestock health at high concentration levels in water resources. Among the different techniques of nitrate removal, adsorption method has attracted attention, due to simplicity, cost-effectiveness, and efficiency. In this research, the effect of variables pH (4, 6, and 8), flow rate (8, 11, and 16 mL/min), bed height (40, 50, and 60 cm), and column diameter (45, 57, and 67 mm) were investigated on nitrate removal from aqueous solutions by modified zeolites column. The BET analysis was used to determine the specific surface and diameter of the pores. Structure and morphology of zeolite was determined using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). For modification of zeolite levels, the hexadecyltrimethylammonium bromide solution with concentration of 25 mM was used. The agricultural drainage water with concentration of 80 mg L-1 nitrate was artificially prepared by dissolving potassium nitrate salt in distilled water in the laboratory. The result of the analysis showed that the zeolite sample was from the clinoptilolite type, with specific surface area and mean pore diameter of 11.984 m2g-1 and 15.295 nm, respectively. The results also showed that changes in pH, flow rate, bed height, and column diameter on different indexes of breakthrough curve were significant at 5% level. The maximum adsorption rate occurred at pH=6, while the maximum adsorption efficiency (65.24%) occurred at pH= 8. The reduction of the flow rate caused increase in nitrate removal efficiency, but the highest amount of adsorption (0.2 mg g-1) occurred at a flow rate of 11 mL/min. The highest amount of absorption and removal efficiency occurred at the bed height and column diameter of 60 cm and 67 mm, respectively.