Nitrate removal from groundwater using catalytic reduction

Nitrate ((NO3-) 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 NO3- remov al. The objective of this study was to develop a catalytic reduction proces s to selectively remove NO3- 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 1 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 pro cess 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 N O3- and NO2- (nitrite) with ion chromatography (IC). Initial NO3- concentra tions ranged between 32 and 41 mg/l. Among the three catalysts, Rh was most effective in removing NO3- Results suggest that Ph catalyst at --400mV and 6 h reaction time can decrease NO3- concentration from 40 to 11.9 mg/l. Du ring the NO3- reduction process NO2- was not detected. The re-oxidation of formerly reduced samples to 390 mV resulted in no increase in the concentra tion of NO3-. Application of a small flow of current to the catalytic reduc tion process increased NO3- reduction rates significantly. For instance, ap plication of 4.6-6.1 v to -250 mV and 6 h of reaction time decreased NO, co ncentration from 40 to 7.9 mg/l. The catalytic reduction process described in this study is useful in removing NO3- from groundwater associated with n onpoint source pollution. (C) 2000 Elsevier Science Ltd. All rights reserve d.