Electrocatalytic reduction of nitrate in water

Nitrate (NO3) contamination of groundwater is a common problem throughout intensive agricultural areas (nonpoint source pollution). Current processes (e.g., ion exchange, membrane separation) for NO3 removal have various disadvantages. The objective of this study was to evaluate an electrocatalytic reduction process to selectively remove NO3 from groundwater associated with small agricultural communities. A commercially available ELAT (E-Tek Inc., Natick, MA) carbon cloth with a 30% surface coated Rh (rhodium) (1 (mu)g cm1) was tested at an applied potential of –1.5 V versus standard calomel electrode (SCE) with a Pt auxiliary electrode. Electrocatalytic reduction process (electrolysis) of NO3 was tested with cyclic voltammetry (CV) in samples containing NO3 and 0.1 M NaClO4. Nitrate and NO2 concentrations in test solutions and groundwater samples were analyzed by ion chromatography (IC). The presence of Rh on the carbon cloth surface resulted in current increase of 36% over uncoated carbon cloths. The electrocatalysis experiments using Rh coated carbon cloth resulted in reduction of NO3 and NO2 on a timescale of minutes. Nitrite is produced as a product, but is rapidly consumed upon further electrolysis. Field groundwater samples subjected to electrocatalysis experiments, without the addition of NaClO4 electrolyte, also exhibited removal of NO3 on a timescale of minutes. Overall, results suggest that at an applied potential of –1.5 V with respect to SCE, Rh coated carbon cloth can reduce NO3 concentrations in field groundwater samples from 73 to 39 mg/L (16.58 to 8.82 mg/L as N) on a timescale range of 40–60 min. The electrocatalytic reduction process described in this study may prove useful for removing NO3 and NO2 from groundwater associated with nonpoint source pollution.