Electrocatalytic reduction of nitrate in water

Abstract

Nitrate (NO 3 −) contamination of groundwater is a common problem throughout intensive agricultural areas (nonpoint source pollution). Current processes (e.g., ion exchange, membrane separation) for NO 3 − removal have various disadvantages. The objective of this study was to evaluate an electrocatalytic reduction process to selectively remove NO 3 − 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 μg cm −1) 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 NO 3 − was tested with cyclic voltammetry (CV) in samples containing NO 3 − and 0.1 M NaClO 4 −. Nitrate and NO 2 − 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 NO 3 − and NO 2 − 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 NaClO 4 − electrolyte, also exhibited removal of NO 3 − 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 NO 3 − 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 NO 3 − and NO 2 − from groundwater associated with nonpoint source pollution.