Chemical Engineering Journal, Vol.160, No.1, 185-189, 2010
Prevention of iron passivation and enhancement of nitrate reduction by electron supplementation
Zero-valent iron (ZVI) permeable reactive barriers (PRB) are susceptible to passivation due to both surface oxidation and the potential accumulation of oxidized mineral species. In this study, we investigated electrically induced reduction (EIR) as a supplemental electron source to rejuvenate passivated ZVI material and aid in resumption of nitrate reduction. In bench reactors. ZVI granules were added to the groundwater containing elevated concentration of nitrate (approximately 5000 mg/L). Nitrate reduction proceeded actively (an average rate of 6.9 mg/L/h) for approximately 48 h then decreased sharply until reaching a complete halt, suggesting severe ZVI passivation. In reactors supplemented with low voltage of direct current (DC), nitrate reduction resumed at a rate of 10.2 mg/L/h within 408 h, which was 47.8% faster than in the ZVI reactor without supplemented current. This robust activity was sustained for more than 1000 h. X-ray diffraction (XRD) analysis indicates there are, as hypothesized, different mineral phases formed on the ZVI depending on whether or not current is applied, suggesting that ZVI passivation may be both avoided and/or reversed by EIR, which also enhances the efficiency of ZVI for reducing nitrate and other reducible constituents. The results suggest that EIR can enhance the removal rate of reducible compounds and positive influence on the long-term performance of PRB. (C) 2010 Elsevier B.V. All rights reserved.