Nitrate removal in potable groundwater by nano zerovalent iron under oxic conditions

Abstract

Groundwater pollution by nitrate contamination has become a significant issue in some areas of Sri Lanka, giving rise to health concerns and a dearth in good quality potable water. In this study, the effectiveness of nano zerovalent iron (nZVI) for the removal of nitrate in potable groundwater under oxic conditions was investigated to meet the drinking water quality standards stipulated by World Health Organization (WHO) and Sri Lanka Standards Institution (SLSI) (nitrate level <50 mg/L). Under oxic conditions, the nZVI was synthesized and batch experiments were conducted using an artificial nitrate (150 mg/L) contaminated water sample. Our results corroborated that with an optimum nZVI dose of 1 g/L and optimum contact time of 30 minutes, 80% nitrate removal could be achieved and the remaining nitrate level was ≈ 30 mg/L as nitrate (<50 mg/L), which was equivalent to ≈ 7 mg/L as nitrate–N (≈21% of the total–N). Ammonium ions were the main product of nitrate reduction by nZVI and at 30 minutes contact time, ≈ 20 mg/L of ammonium as ammonium–N was detected (≈ 59% of the total–N). Ammonia stripping took place under the basic solution pH (pH > 9.5). At 30 minutes of contact time, ≈7 mg/L of ammonia as ammonia–N was accounted for ammonia stripping, which is 20% of the total–N. Ammonia stripping resulted in a decrease in nitrogen-containing species in the aqueous phase. The spent nZVI particles were recovered (99.9%) from the treated water using an external magnetic field. In conclusion, nZVI particles synthesized under oxic conditions are viable to successfully treat the nitrate-contaminated groundwater under aerobic conditions to reduce the nitrate levels to meet the WHO/SLSI drinking water quality standards.