Extent Of Nitrate Removal Research Articles

Chemical Reduction of Nitrate in Aqueous Solution by Iron Powder

Nitrate is a common groundwater contaminant and poses health and environmental threats. Reductive denitrification of nitrate by zero-valent iron was investigated in unbuffered solutions at 20 °C. Nitrate was effectively removed at low initial solution pH. The reaction was accompanied by the production and then disappearance of a small quantity of nitrite, suggesting that nitrite was the intermediate and subsequently further reduced. A rapid rise in solution pH was also observed during the reaction. At the initial pH of 4, a reduction of 90% in nitrate concentration from 60 to 7.0 mg/L at 60 min was observed. The extent of nitrate removal decreased with increasing solution pH within the tested range of 3 - 6, suggesting that the reaction was an acid-driven process. The extent of nitrate removal also increased with Fe dosage over the range of 5 - 20 g/L, as higher Fe dosages provided more reactive surfaces. It is proposed that protons participate in the nitrate reduction by Fe0 via an initial reduction of protons to reduced hydrogen species followed by a subsequent reaction with nitrate. The hydrolysis of Fe corrosion products (e.g., ferrous ions) produces protons, in particular, near the surfaces of Fe, which drives the reaction to continue.

Nitrate reduction by metallic iron

Chemical reduction of nitrate by metallic iron (Fe 0) was studied as a potential technology to remove nitrate from water. The effects of pH and the iron-to-nitrate ratio on both nitrate reduction rate and percent removal were investigated. Rate constants and the apparent reaction order with respect to nitrate were determined and a mass balance was obtained. Rapid nitrate reduction by iron powder was observed only at pH≤4. pH control with sulfuric acid significantly prolonged nitrate reduction and increased the percent removal. At high nitrate loadings, both the rate and the percent removal increased with decreasing pH. An iron-to-nitrate ratio of 120 m 2 Fe 0/mol NO 3 or higher was required to completely remove nitrate within an hour. An apparent reaction order of 1.7 with respect to nitrate was observed, which may be partly due to the inhibitory effect of sulfate. Ammonia was the end product of nitrate reduction and accounted for all nitrate transformed under our experimental conditions. Acidity is the principal factor which controls the rate and the extent of nitrate removal by Fe 0. The rapid reduction of nitrate at low pH was most likely due to either direct reduction by Fe 0 or indirect reduction by surface hydrogen derived from proton. Ferrous species, Fe 2+ and Fe(OH) 2, were probably not involved in this reaction.

Hardness and Salt Effects on Catalytic Hydrogenation of Aqueous Nitrate Solutions

Liquid-phase hydrogenation using a solid Pd–Cu bimetallic catalyst provides a potential technique for the removal of nitrates from waters. In this study, hardness and salt effects on both the nitrate disappearance rate and the reaction selectivity were quantitatively evaluated. Reduction experiments were performed for a wide range of nitrate conversions in an isothermal semibatch slurry reactor. It was discovered in a series of runs using various nitrate salts as a source of nitrate ions that the apparent surface reaction rate constant increases in the order K+<Na+<Ca2+<Mg2+<Al3+and changes proportionally with the ionization potential of a cation present in the aqueous solution. Permanent hardness of drinking water exhibits no inhibitive impact either on the extent of nitrate removal or on reaction selectivity. On the other hand, the nitrate disappearance rate as well as nitrogen production yield decrease appreciably in the presence of hydrogencarbonates, which is attributed to identical structures of nitrate and hydrogencarbonate ions resulting in competitive adsorption of these species to Pd–Cu active sites. A detailed analysis of experimental data confirmed that efficiency of the Pd–Cu bimetallic catalyst in catalytic nitrate reduction is influenced by the migration of produced hydroxide ions from the Helmholtz layer.