Nitrate reduction by micro-scale zero-valent iron particles under oxic condition

Abstract

The denitrification by zero-valent iron (ZVI) particles under oxic condition at various conditions was investigated in this study. After a 2-h reaction under oxic condition, NO3−-N removal and conversion to NH4+-N was 97.6% and 35.2%, respectively, when the initial NO3−-N concentration was 25 mg/L, the dose of 85 μm ZVI was 2 g/L, and the initial pH was 2.0. The injection of an additional electron doner (50 mg/L Fe2+) did not promote the reaction, but the initial pH greatly affects NO3−-N reduction, regardless of the presence of Fe2+. Phosphate promoted and inhibited NO3−-N sorption and reduction at low and high concentration, respectively, suggesting its role of both electron transfer enhancement and competition. The results of continuous experiments using a horizontal flow ZVI reactor showed that NO3−-N reduction efficiency was in a range of 88-100%, through a 1700 h operation. In addition, field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) analysis, and X-ray diffraction (XRD) analysis showed that hematite is the major reaction products of ZVI under oxic condition. The results in this study suggest that ZVI can successfully be used for denitrification under oxic condition, which can be an advantage over nano-scale ZVI.