Combined influence of some cations on arsenic removal by an air-injectioec reactor using aluminum ball electrodes

Combined effects of some cations such as calcium (Ca²⁺), iron (Fe²⁺), manganese (Mn²⁺), and mag-nesium (Mg²⁺) and operating time on the removal of arsenic by air-injected electrocoagulation (EC) reactor with aluminum (Al) ball electrodes were investigated. The operating conditions were opti-mized with the Box–Behnken design of response surface methodology (RSM). The response vari-ables were selected from the program as removal efficiency, residual arsenic concentration, energy consumption and operating cost (OC) in the EC process. A total of 46 experimental run was performed. The removal efficiency of arsenic increased with an increase in iron concentration (0.5–4.5 mg/L). The rest of the cations showed no noticeable effect on arsenic removal efficiency. The maximum arsenic removal efficiency and minimum OC at the optimum operating conditions (C_Ca: 305 mg/L, C_Mg: 42 mg/L, C_Fe: 3.3 mg/L, C_Mn: 2.34 mg/L, initial pH of 7.5 applied current of 0.15 A, Al ball size of 7.5 mm, 5.0 cm of Al ball anodes height in the EC reactor, air-fed rate of 6.0 L/min and t_EC: 16.83 min) in the EC process were 99.9% and 0.0332 $/m³ for initial arsenic concentration of 200 μg/L, respec-tively. The removal mechanism of As(III) by EC seems to be oxidation of As(III) to As(V) and sub-sequent removal by adsorption/complexation with aluminum hydroxides generated in the process. The results showed that the air-injected EC reactor can be used effectively for arsenic and hardness removal simultaneously from real groundwater sources.