Chemical removal of nitrate from water


HIGH levels of nitrate in ground water can pose a serious health risk. Reduction of nitrate to nitrite in the gut may cause methemoglobinaemia1both in newborn infants and in adults deficient in glucose-phosphate dehydrogenase2. Under abnormal circumstances, reduction to nitrite can also occur in the stomach to form N-nitrosamines, a postulated cause of stomach cancer3. Nitrate outflow onto shallow continental shelves can promote nearshore algal blooms. Both natural and anthropogenic sources contribute to nitrate pollution. In the United States4 and Europe5, legislation now specifies a maximum permissible nitrate level in drinking water. Techniques such as selective ion exchange6, reverse osmosis, electrodialysis and distillation exist to transfer nitrate between two bodies of water, but only biological processes are presently available for nitrate destruction. Here I describe a chemical process in which aluminium powder reduces nitrate to ammonia, nitrogen and nitrite. In a pH range of 9 to 10.5, selective reduction of nitrate relative to sulphate is possible, and between pH 9.1 and 9.3, loss of the reductant through decomposition of water can be minimized to less than 2%. Subsequent control of pH and concentrations of dissolved aluminium, nitrite and ammonia should be possible at a realistic cost, making this process potentially useful for combating nitrate pollution.

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Murphy, A. Chemical removal of nitrate from water. Nature 350, 223–225 (1991).

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