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.