Electrokinetic pretreatment of seawater to decrease the Ca^2 +, Mg^2 +, SO₄^2 − and bacteria contents in membrane desalination applications

Electrokinetic cells with three different electrode arrangements were supplied with raw seawater collected from the Gulf. The electrode arrangements included anode-cathode (A-C), anode-cathode-cathode-anode (A-C-C-A), and cylindrical (three cathodes surrounded by an anode) configurations. The electrokinetic cells were tested at different current densities ranging from 0.05 to 0.2 mA/cm² for 6 h. The results showed that inorganic ions and bacteria removal increased with increasing current density. For example, at a current density of 0.2 mA/cm², 78, 76, and 91% of the Mg^2 + ions were removed by the A-C, A-C-C-A, and cylindrical configurations, respectively, whereas these cells removed 64, 63, and 51% of the Mg^2 + ions, respectively, at a current density of 0.1 mA/cm². In addition, the A-C, A-C-C-A, and cylindrical cells removed 21, 40, and 44% of the Ca^2 + ions, respectively, and 47, 79, and 79% of the SO₄^2 − ions, respectively, at a current density of 0.2 mA/cm². The removal efficiencies obtained with the A-C, A-C-C-A, and cylindrical cells were 15, 18, and 13%, respectively, for Ca^2 + and 47, 26, and 22%, respectively, for SO₄^2 − at a current density of 0.1 mA/cm². Furthermore, nearly all of the bacteria were removed under the tested operating conditions (total bacteria count (TBC) was zero).