Nitrate removal from groundwater using catalytic reduction

Nitrate ((NO−3) contamination of groundwater is a major concern throughout intensive agricultural areas (nonpoint source pollution). Current processes (e.g., ion exchange, membrane separation) are not selective for NO−3 removal. The objective of this study was to develop a catalytic reduction process to selectively remove NO−3 from groundwater associated with agricultural community. Three catalysts, palladium (Pd), platinum (Pt), and rhodium (Rh) on carbon (5–10%) were tested in this study. A l of groundwater sample was amended with 0.5 g catalyst and reacted at different redox potentials (340 to −400 mV) and reaction times (1–6 h). During the catalytic reduction process the pH was maintained around 6.5 by bubbling 5% carbon dioxide (CO2). At a given redox potential and reaction period, samples were analyzed for NO−3 and NO−2 (nitrite) with ion chromatography (IC). Initial NO−3 concentrations ranged between 32 and 41 mg/l. Among the three catalysts, Rh was most effective in removing NO−3. Results suggest that Rh catalyst at −400 mV and 6 h reaction time can decrease NO−3 concentration from 40 to 11.9 mg/l. During the NO−3 reduction process NO−2 was not detected. The re-oxidation of formerly reduced samples to 390 mV resulted in no increase in the concentration of NO−3. Application of a small flow of current to the catalytic reduction process increased NO−3 reduction rates significantly. For instance, application of 4.6–6.1 ν to −250 mV and 6 h of reaction time decreased NO−3 concentration from 40 to 7.9 mg/l. The catalytic reduction process described in this study is useful in removing NO−3 from groundwater associated with nonpoint source pollution.