Unravelling the potential of combined electrodialysis/electrocoagulation for boosted dye removal and membrane...

Membrane fouling is the major technology issue facing the wide application of electrodialysis (ED) for water purification in real world cases. The fouling of membrane in ED leads to reduce the removal rate, increase in membrane damage, and it requires continuous costly maintenance. Herein, a successful dual process combining ED and electrocoagulation (EC) was designed to combat anionic membrane (AMX) fouling and to boost organic dye pollutant (methyl orange, (MO)) removal efficiency. Electrodialysis-electrocoagulation (ED-EC) was constructed via the use of cheap aluminum anode. In such a combined system, coagulation synergistically accumulates and eliminates MO species, and meanwhile, the separation of mineral (Na⁺ and Cl^-) occurs by ED mechanism. A performance comparison between single ED and ED-EC demonstrates technological, economic, and efficiency benefits of combined ED-EC process as compared to single ED. The MO removal rate was improved from 20.72 to 96.92%, the electrical resistance of the ED cell (EREDC) was reduced by 40%, and the amount of Cl^- ions transferred was boosted by twice. Membrane surface characterization proved that AMX membrane fouling was very intense in single ED due to MO fixation and accumulation on the membrane pores, which in turn makes the process unable to function effectively and continuously. On the contrary, ED-EC exhibits excellent mass transfer and boosted continuous removal without any observed increase in the electrical resistance of the dual cell. To further understand synergistic performance of dual ED-EC, experiments were carried out under different operating conditions including variation in current density, variation in MO concentration, and changes in pH and NaCl electrolyte dose. Highest efficiency using dual system was recorded at pH close to neutral, while the removal at alkaline or acidic solutions. The final sludge obtained after the treatment was characterized via SEM-EDS, XRD, and FTIR techniques. Overall, this study proves the correlation between ED and EC to build a dual process allowing highly efficiency and continuous processing which are the crucial factors that are wanted at real-world application.