Study of ferrous iron oxidation in Morocco drinking water in an airlift reactor

Although ferrous iron removal from drinking water by aeration has been studied for a while, there is still an uncertainty on the performance and the physicochemical mechanisms of iron(II) oxidation [S.K. Sharma, B. Petrusevski, J.C. Schippers, J. Water. Supply Res. Technol. Aqua, 54 (2005) 239–247]. A possible reason is the autocatalytic effect of ferric hydroxide particles, but this assumption is never validated quantitatively in practice because this catalytic effect has been investigated only under batch laboratory-controlled conditions. In this work, iron(II) oxidation has been studied on synthetic waters in a 63 L split-rectangular airlift reactor, the hydrodynamics and the mass transfer properties of which were described previously [N. El Azher, B. Gourich, C. Vial, M. Belhaj Soulami, A. Bouzidi, M. Ziyad, Biochem. Eng. J., 23 (2005) 161–167]. Experiments were carried out both under semi-batch and continuous flow conditions. The kinetic parameters derived from the experiments were consistent with the literature both under unsteady and steady-state conditions. Experimental results showed that the airlift reactor allowed simultaneously good mixing, mass transfer and pH control despite the strong sensitivity of the oxidation kinetics to pH. Data confirmed that recycling about 50 mg/L of ferric hydroxide particles in a slurry phase could decrease drastically the time necessary to reach the minimum admissible concentration of iron(II). For example, residence time could be reduced by a factor six at pH 7.0 under steady-state conditions, which may avoid the need for a further pH increase.