Influence of solution composition and column aging on the reduction of nitroaromatic compounds by zero-valent iron

Granular iron is used in reactive permeable barriers for the reductive trea tment of organic and inorganic groundwater contaminants. The technology is well established, however, its long-term performance and the importance of the groundwater composition are not yet well understood. Here, the influenc e of chloride, nitrate, silicate, and Aldrich humic acid on the reactivity of Master Builder iron was studied under anoxic conditions using small pack ed columns and 2-nitrotoluene (2-NT) as a model contaminant. After initiall y complete reduction of 2-NT to 2-aminotoluene (2-AT) in the column, possib ly under mass-transfer controlled conditions, the reactivity of the iron wa s found to decrease substantially. In the presence of chloride, this decrea se was slowed while exposure to silicate resulted in a very quick loss of i ron reactivity. Nitrate was found to interfere strongly with the effect of chloride. These observations are interpreted in terms of corrosion inhibiti on/promotion and competition. Our results suggest that reactive barrier per formance may be strongly affected by the composition of the treated groundw ater. (C) 2001 Elsevier Science Ltd. All rights reserved.