Removal of Nitrate in the Aqueous Phase Using Granular Ferric Hydroxide

Abstract

Background: In recent years, the nitrate concentration in surface water and especially in groundwater was increased significantly in many parts of Iran. Objectives: The main objectives of this study were to evaluate the feasibility of using granular ferric hydroxide (GFH) to remove nitrate from aqueous phase as well as to determine the removal efficiency at the optimal condition. Materials and Methods: The present study was conducted on a bench scale experiment. The spectrophotometer DR5000 (wavelength 520 nm) was used to determine the nitrate concentration. The effect of influencing parameters including pH at 5 levels (3.8 - 7.8), initial nitrate concentration at 4 levels (50 - 150 mg/L) the amount of adsorbent dose (0.625, 1.25, 2.5, 3.75 g/50mL), the effects of interfering ions, such as sulfate ions at 4 levels (200 - 800 mg/L) and chloride ions at 4 levels (200 - 800 mg/L), and contact time at 3 levels (30 - 90 minutes) were studied. Results: Based on our data, pH of 4.8, adsorbent dose of 3.75 g and contact time of 90 minutes is optimal for nitrate removal. Furthermore, the nitrate reduction rate was increased rapidly by the addition of the adsorbent and decreased by nitrate addition. The nitrate reduction rate was increased by increasing the contact time. The percent of nitrate reduction was significantly enhanced by decreasing the pH (from 7.8 to 8.4) and then reached a plateau with a relative slow equilibration. Moreover, adsorption efficiency was significantly decreased in the presence of interfering ions, such as sulfate and chloride ions. Conclusions: In conclusion, GFH can be used as a reliable and appropriate method with high efficiency for the reduction of nitrate in many polluted water resources.