Fractional factorial design of water desalination by neutralization dialysis process: concentration, flow rate, and volume effects

This work concerns the optimization of the neutralization dialysis process applied to water desalination. This process is used for salt removal from a NaCl model solution (initially 0.08 M) in a three-compartment membrane stack (acid, salt, and alkali compartments) with a cation-exchange membrane and an anion-exchange one, i.e. Neosepta® CMX and AMX, respectively. The desalination process has been investigated as a function of three main parameters, namely the initial concentration and the flow rate of acidic and alkaline solutions as well as the saline solution volume. A fractional factorial design, i.e. 25−1, has been employed to assess the parameters affecting the desalination efficiency, and specifically to study the ion-exchange of H+ and Na+ through CMX and that of OH− and Cl− through AMX. A linear theoretical model based on the experimental results has been carried out to account for the influence of the different parameters investigated and their relative interactions. The analysis of variance and student's T-tests have shown that the initial alkaline solution concentration and the saline solution volume are the most statistically significant parameters affecting the ion transport of H+/Na+ and OH−/Cl− through CMX and AMX, respectively, as well as the desalination duration.