Nitrate removal from aqueous solutions by γ-Al2O3 ultrafiltration membranes

In the framework of understanding the transport mechanism that governs the filtration of NO3- solution through a γ-Al2O3 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 NO3- concentration on the selectivity and permeability of the membrane were studied using binary solutions (KNO3, NaNO3, Ca(NO3)2 and Mg(NO3)2) and ternary solutions ((NaNO3 + KNO3), (NaNO3 + Ca(NO3)2) and (Mg(NO3)2 + Ca(NO3)2). The experimental filtration results showed that high NO3- rejection was observed when pH was close to the point of zero charge of the membrane for both binary and ternary solutions. NO3- rejection increased with an increase of applied pressure. The rejection gradually decreased when the initial NO3- concentration increased. It appeared that the valency and hydrated radius of associated cation had a dramatic effect on NO3- 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 NO3- from two different sources were studied at optimized operating conditions (25 ppm of NO3- and 6 bar). Experimental results demonstrated that NO3- 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-Al2O3 ultrafiltration membrane for denitrificatoin of contaminated water especially in Moroccan agricultural areas.