Effect of Humic Acid and Acidity on Nitrate Removal from Water Using Zero Valent Iron Nanoparticles (FeNps)

Nitrate is a wide spread pollutant whose removal from aquesous solutions is a major goal of water treatment processes. The present experiment was conducted using a randomized complete block split design with three replications to investigate the effects of humic acid on the nitrate removal efficiency of nanoscale zero-valent iron particles. For this purpose, nanoscale zero-valent iron particles were synthesized using the co-precipitation method and stabilized on sand fractions to achieve better stability in the water environment. Different concentrations of humic acid (0, 0.25, and 0.75 mg/l) and nanoscale zero-valent iron particles (1, 1.5, and 2 mg/l) were used as the variables to evaluate the resulting changes in the water nitrate content. Results showed that nanoscale zero-valent iron particles were able to reduce nitrate ions and, thereby, remove it from the solution. Humic acid was found to reduce the nitrate removal efficiency of nanoscale zero-valent iron particles. The highest nitrate removal (58%) occurred at pH 4 with a nanoscale zero-valent iron concentration of 1 mg/l while the lowest was observed at pH 3.7% with a nanoscale zero-valent iron concentration of 2 mg/l. Humic acid, especially at its lower concentrations, also proved to be an important factor involved in reducing nitrate. In the absence of humic acid, the highest nitrate reduction efficiency of 44% was observed at pH 4. Finally, a pH value of 4 was found to be the optimum level for nitrate removal, which led to an average removal efficiency of 34%.