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 NO sub(3) super(-), by Fe super(0) is reported here. The anaerobic reduction of NO sub(3) super(-) was carried out using Fe super(0) 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 sub(2)SO sub(4), or CH sub(3)COOH, because the Fe oxidation and NO sub(3) super(-) reduction reactions consume acidity. Under the conditions of this study, NH sub(3)/NH sub(4) super(+) were the only N products. The formation of green rusts divided the NO sub(3) super(-) reduction process into two phases. Green rusts formed around a pH of 6.5 and contributed to the stabilization of pH. With H sub(2)SO sub(4), the available Fe surface area was limited, initially by the excessive accumulation of H sub(2) gas at the interface, which inhibited NO sub(3) super(-) reduction. The surface area normalized pseudo-first order reaction rates for NO sub(3) super(-) reduction at pH>6.5 or after the formation of green rusts are consistent with those reported for buffered solutions.