Nitrate removal from aqueous solutions by γ-Al(2)O(3) ultrafiltration membranes

In the framework of understanding the transport mechanism that governs the filtration of NO(3)(−) solution through a γ-Al(2)O(3) membrane with a nominal pore size of 5 nm at low ultrafiltration, a series of various types of nitrate solutions and operating conditions were investigated. The effect of filtration parameters such as pH, applied pressure and NO(3)(−) concentration on the selectivity and permeability of the membrane were studied using binary solutions (KNO(3), NaNO(3), Ca(NO(3))(2) and Mg(NO(3))(2)) and ternary solutions ((NaNO(3) + KNO(3)), (NaNO(3) + Ca(NO(3))(2)) and (Mg(NO(3))(2) + Ca(NO(3))(2)). The experimental filtration results showed that high NO(3)(−) rejection was observed when pH was close to the point of zero charge of the membrane for both binary and ternary solutions. NO(3)(−) rejection increased with an increase of applied pressure. The rejection gradually decreased when the initial NO(3)(−) concentration increased. It appeared that the valency and hydrated radius of associated cation had a dramatic effect on NO(3)(−) rejection, with the divalent cations being more rejected than monovalent cations. In order to get to natural water complexity, three different samples of mineral water doped with NO(3)(−) from two different sources were studied at optimized operating conditions (25 ppm of NO(3)(−) and 6 bar). Experimental results demonstrated that NO(3)(−) rejection strongly depended upon the total mineralization and the presence of divalent anions in solution. In addition, the obtained results showed the potential use of γ-Al(2)O(3) ultrafiltration membrane for denitrificatoin of contaminated water especially in Moroccan agricultural areas.