Treatment of potable water containing low concentration of arsenic with electrocoagulation: Different connection modes and Fe-Al electrodes

In this study, effects of both Fe and Al electrode connection modes (parallel and series) and electrode materials on arsenic removal efficiency from potable water by electrocoagulation (EC) process were investigated. Experiments were carried out to remove arsenic by the EC covering wide range in operating conditions such as pH (4-9), current density (1.75-7.5 A/m(2)) and operating time (0-15 min). The highest arsenic removal was obtained in the monopolar series (MP-S) electrode connection mode for both electrodes as pH 6.5 for Fe and pH 7 for Al electrodes to achieve a residual arsenic concentration of 10 mu g/L or less for potable water in the EC process. As the current density increased, arsenic removal efficiencies were increased with all types of electrode connection modes. However, the optimum arsenic removal at 2.5 A/m(2) was obtained with 2.5 min of operating time for Fe (94.1%) and 4 min of operating time (93.5%) for Al electrodes at MP-S mode. The electrode and energy consumption values at MP-S connection mode for Fe and Al electrodes were calculated as 0.00140 kg Fe/m(3) and 0.0025 kg Al/m(3), and 0.0140 kWh/m(3) and 0.0254 kWh/m(3), respectively. Therefore, the lowest operating costs were 0.0047 epsilon/m(3) and 0.0064 epsilon/m(3) for Fe and Al electrodes. The optimum arsenic removal from potable water by the EC process showed that Fe electrodes gave the best results at MP-S connection mode as compared to the rest in terms of operating time and operating cost. The sludge was analyzed using scanning electron microscope (SEM) imaging. The SEM image suggested that amorphous Fe/Al oxyhydroxides were present in the sludge. (C) 2010 Elsevier B.V. All rights reserved.