Effects of coexisting ions on simultaneous removal of fluoride and arsenic from water by hybrid Al–Fe electrocoagulation

This study investigated the effects of coexisting ions in water (calcium, magnesium, nitrate, sulphate and carbonates) on the simultaneous removal of fluoride (16 mg/L) and arsenic (200 µg/L) using hybrid Al–Fe electrocoagulation. Experiments were conducted at operation conditions of J = 9.9 mA/cm2, pH = 7.5 and 50 min. The analysis of variance results for all variables confirmed the predicted models by the experimental design R2 of 0.69 and 0.72% for fluoride and arsenic, respectively, which ensured a satisfactory adjustment of the quadratic models with the experimental data. The results showed that calcium (0.5–100 mg/L) enhanced fluoride removal, while sulphate (> 80 mg/L) and nitrate (> 75 mg/L) suppressed the fluoride removal. On the other hand, nitrate (0.5–100 mg/L), sulphate (> 50 mg/L), magnesium (> 50 mg/L) and calcium (> 50 mg/L) reduced arsenic removal. The combination of magnesium (< 70 mg/L) and calcium appeared to increase the fluoride removal, while the combination of other ions had antagonistic effects on the removal of both fluoride and arsenic. Carbonates showed an insignificant influence on the removal of both pollutants. The effects of coexisting ions on the performance of hybrid Al–Fe EC were found to depend on the type and concentration of individual coexisting ion.