Fluoride removal efficiencies of Al-EC and Fe-EC reactors: process optimization using Box–Behnken design of the surface response methodology

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Abstract In this study, surface response methodology was employed to investigate the effect of different interacting factors on the removal of fluoride from synthetic water using aluminum electrocoagulation (Al-EC) and iron electrocoagulation (Fe-EC) in different reactors. Box–Behnken design of a Design Expert version 11 was used for the optimization and evaluation of the process independent variables: applied electric density, initial pH, initial fluoride concentration and treatment time on the efficiency of fluoride removal as a response. Results showed that the effect of current density and initial fluoride concentration was significant model terms for fluoride reduction in Fe-EC and Al-EC reactors, respectively. The Al-EC reactor model presented the R2 value of 79.2% while Fe-EC presented R2 value of 75.8%, showing that both models can predict the response well. The reduction by 94% (initial concentration of 16 mgF/L) was established at optimal operating parameters of 18.5 mAcm−2, pH 6.80 in 50 min using Al-EC. On the other hand, 16 mgF/L was reduced by 92% to 1.28 mgF/L in Fe-EC reactor at optimal condition of 6.5 mAcm−2, pH 6.50 in 50 min. Experimental results correlated well to the model predicted results that were 95 and 94% for Al-EC and Fe-EC, respectively. Both reactors manage to reduce fluoride to a level recommended by WHO (≤ 1.5 mg/L) for drinking purpose.

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