Use of Nanoscale Zero-Valent Iron (NZVI) Particles for Chemical Denitrification under Different Operating Conditions

Abstract

Abstract:The nitrate pollution of waters and groundwaters is an important environmental and health concern. An interesting method to remove the oxidized forms of nitrogen from waters and wastewaters is chemical denitrification by means of metallic iron (Fe 0 ).Particularly advantageous is the use of nanoscopic zero-valent iron particles due to the elevated surface area, which allows reaching extremely high reaction rates. In the present paper, the efficiency of nitrate reduction by means of nanoscopic Fe 0 has been investigated under several operating conditions. The iron nanoparticles were synthesized by the chemical reduction of ferric ions with sodium borohydride. The effects of Fe 0 dosage, initial N-NO3 − concentration and pH on chemical denitrification were identified. In particular, the results of the tests carried out showed that it is possible to reach an almost complete nitrate reduction in treating solutions with a nitrate nitrogen concentration higher than 50 mg/L. Moreover, the process performance was satisfactory also under uncontrolled pH. By means of the trends detected during the experiments, the kinetic-type reaction was identified. Furthermore, a relation between the kinetic constant and the process parameters was defined.

Removal of Nitrate from Drinking Water by Ion-Exchange Followed by nZVI-Based Reduction and Electrooxidation of the Ammonia Product to N2(g)

“…They reported on increased reaction rate at the higher Fe to NO 3 − ratio. A similar observation was reported by Siciliano [24]. On the other hand, Yang and Lee [17] reported that the nitrate reduction rate decreased at a higher Fe to NO 3 − ratio when lower nitrate concentrations were applied, while the Fe dosage was maintained constant (at pH 4).…”

“…This is also shown by another comparison, in which a higher reaction rate was reported at the same Fe to NO 3 − molar ratio when the initial Fe and NO 3 − concentrations were higher [17]. However, examining the results reported by Siciliano [24] leads to opposite conclusions: lower reaction rates were observed when the reactant concentrations were elevated, while the molar ratio between Fe and NO 3 − was kept almost constant. In addition, a decrease in the reaction rate at higher nitrate concentrations (accompanied by a decrease in the molar Fe to NO 3 − ratio) was observed in experiments in which the pH was both controlled and not controlled ( [24] and [15], respectively).…”

“…However, examining the results reported by Siciliano [24] leads to opposite conclusions: lower reaction rates were observed when the reactant concentrations were elevated, while the molar ratio between Fe and NO 3 − was kept almost constant. In addition, a decrease in the reaction rate at higher nitrate concentrations (accompanied by a decrease in the molar Fe to NO 3 − ratio) was observed in experiments in which the pH was both controlled and not controlled ( [24] and [15], respectively). When the pH was not controlled, high nitrate concentrations promoted faster reaction and thus a rapid pH increase (due to proton consumption), at which conditions of the reaction kinetics slowed down, as mentioned above.…”

“…This observation seems reasonable, since protons are consumed in Equation (1). Siciliano [24] also suggested that the higher reaction rate at low pH might be related in part to H + -induced iron oxidation occurring at the acidic solutions. Accordingly, these authors defined the mechanism as "acid-driven surface mediated process".…”

“…Comparing results from different works is problematic since, in some studies, the pH was not controlled and thus fluctuated in a wide range covering basic and acidic values [15,19,23], while, in others, it was maintained at a relatively wide, but acidic range of pH 2-5 [17,24]. Several works (e.g., [19,20,24,25]) reported that nitrate reduction by nZVI proceeded more rapidly at acidic conditions. This observation seems reasonable, since protons are consumed in Equation (1).…”