Chemical Reduction Of Nitrate Research Articles

Experimental investigation on the chemical reduction of nitrate from groundwater

Groundwater is a significant source of water. Adverse health effects have been reported when groundwater with a high nitrate concentration is used for drinking purposes. The objective of this paper was to investigate the effectiveness of a new treatment technology for the reduction of nitrate from groundwater. The optimal operating conditions of chemical nitrate reduction with fine aluminum powder are evaluated through controlled laboratory testing using the standard jar-test apparatus. A maximum of 62% nitrate removal was achieved with the following conditions: 300 mg/l aluminum dose, water temperature of 25°C, pH of 10.7, and initial nitrate concentration of 20 mg/l as N. On completion of the treatment, the concentrations of nitrate, nitrite and ammonia were measured as 8.3, 0.26 and 0.50 mg/l as N, respectively, all within the maximum acceptable concentrations (MAC) of the Canadian guidelines. To ensure adequate quality of the treated water, residue concentrations of total aluminum were also measured for several samples following brief sedimentation, and they averaged 0.07 mg/l. This also complies with the Canadian MAC of 0.1 mg/l. In conclusion, chemical nitrate reduction with aluminum powder is demonstrated to be both effective and safe, and the costs associated with the adaptation of this method may be minimized when combined with conventional water softening processes.

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.

Chemical Reduction of Nitrate by Ferrous Iron

AbstractKnowledge concerning the chemical reduction of NO3− to gaseous products, a process of potential practical significance as an antipollution device, is sparse. The influence of pH on chemical reduction of NO3−‐N (approximate concentration 25 ppm) by Fe2+ in the presence and absence of Cu2+ was studied over a pH range from 6 to 10. After 24‐hours of controlled pH incubations under a helium atmosphere NO3−, NO2−, N2O, NO, N2, and NH4+ were determined. The initial Fe2+/NO3− mole ratio was 8. Reduction of NO3− was negligible in the absence of Cu2+, but was pronounced above pH 7 in the presence of approximately 5 ppm Cu2+. Formation of NH4+ increased with pH and was the dominant process at pH 9 and 10. Nitrous oxide and N2 accumulations were greatest in the pH range from 8 to 8.5 and negligible at pH 6 and 10. Nitrite formation was small except at pH 9 and 10. Trace quantities of NO accumulated during incubation if the pH was allowed to drop below 6.Levels of Cu2+ and Fe2+ influenced the extent and nature of NO3− reduction at pH 8. Maximum reduction of NO3− (93%) and maximum gas production (equivalent to 61% of the original NO3−) occurred when the Fe2+/NO3− mole ratio was 12 and the Cu2+ level was approximately 10 ppm. The N2O/N2 mole ratio in the evolved gases decreased as the Cu2+ level was increased from approximately 1 to 10 ppm and as the Fe2+/NO3− mole ratio was increased from 8 to 12. Nitrate was relatively stable at a Cu2+ content of 0.1 ppm irrespective of the Fe2+/NO3− ratio.