Nitrate reduction by zero-valent iron under different pH regimes

Nitrate in drinking water can pose a threat to human health. A study of the reduction of NO₃^-, by Fe⁰ is reported here. The anaerobic reduction of NO₃^- was carried out using Fe⁰ powder in unbuffered solutions from pH 2 to greater than 10. The initial pH of the solution was adjusted to 2, 3, or 4 by addition of HCl, H ₂SO₄, or CH₃COOH, because the Fe oxidation and NO₃^- reduction reactions consume acidity. Under the conditions of this study, NH₃/NH₄⁺ were the only N products. The formation of green rusts divided the NO₃ ^- reduction process into two phases. Green rusts formed around a pH of 6.5 and contributed to the stabilization of pH. With H₂SO ₄, the available Fe surface area was limited, initially by the excessive accumulation of H₂ gas at the interface, which inhibited NO₃^- reduction. The surface area normalized pseudo-first order reaction rates for NO₃^- reduction at pH>6.5 or after the formation of green rusts are consistent with those reported for buffered solutions.