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, H2SO4, 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 H2SO4, 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.