Evaluation of South African Sand/Zero-Valent Iron Combinations for the Treatment of Nitrate-Contaminated Water: Kinetic and Effect of Competitive Ions

Abstract

This study aimed to define the optimum weight ratio between Berea Red sand (BRS)/zero-valent iron (ZVI) combinations to be used in the treatment of nitrate contaminated water. The effect of competing ions (phosphate and sulfate) on the nitrate removal efficiency of the best performing BRS-ZVI w/w ratio was also assessed. To achieve this objective, batch tests were performed under anoxic and acidic conditions (pHi = 4.5), using two combinations: 50%BRS-50%ZVI (w/w) and 25%BRS-75%ZVI (w/w), as well as 100%ZVI as a control. BRS and ZVI had 1 to 2-mm grain size. pH and nitrogen species were tested during these batch tests. Kinetic analysis was also carried out. While the removal efficiencies of 100%ZVI and 25%BRS-75%ZVI (w/w) were 70.2% and 83.1%, respectively, the experimental results showed that the combination of 50%BRS-50%ZVI (w/w) had the highest nitrate removal efficiency (99.5%), implying a synergistic effect between BRS and ZVI. Likewise, the kinetic analysis showed that the nitrate removal rate (k) increased as the BRS mass in the BRS-ZVI combination increased. Furthermore, the presence of phosphate and sulfate negatively affected the nitrate removal performance of the 50%BRS-50%ZVI combination, which was the best performing weight ratio. However, this weight ratio still showed high nitrate removal capacities in the presence of phosphate and sulfate, respectively. The 50%BRS-50%ZVI combination demonstrated to be the optimum among the used ones. However, further investigation in a large-scale reactor on this combination is recommended for further optimization of its performance.