Simultaneous removal of fluoride and arsenic from groundwater by electrocoagulation using a filter-press flow reactor with a three-cell stack

Abstract

Abstract An electrocoagulation (EC) process to remove fluoride and arsenic from groundwater (fluoride 5.5 mg L−1, arsenic 50.4 µg L−1, hydrated silica 132 mg L−1, sulfate 40 mg L−1, nitrate 6.7 mg L−1, phosphate 0.55 mg L−1, hardness 23 mg L−1, alkalinity 59.0 mg L−1, pH 8.5 and conductivity 824.5 µS cm−1) was investigated. The EC was carried out in a filter-press flow reactor, containing a three-cell stack equipped with aluminum electrodes. The influence of current density (j), mean linear flow rate in the EC reactor (ur) and the co-existing ions on the fluoride and arsenic removal efficiencies was analyzed. All EC tests, performed at 0.23 ≤ ur ≤ 0.93 cm s−1 and 5 ≤ j ≤ 7 mA cm−2, satisfied the World Health Organization (WHO) standard for fluoride (CF- ≤ 1.5 mg L−1). The EC tests that satisfied the WHO standard for arsenic (CAs ≤ 10 µg L−1) were at 0.23 cm s−1 and 6 ≤ j ≤ 7 mA cm−2. Spectroscopic analyses on aluminum flocs showed that these are mainly composed of aluminum silicates. Fluoride replaces a hydroxyl group from aluminum flocs and arsenates adsorb on aluminum aggregates. The best EC test in terms of energy consumption (6.7 kWh m−3) was obtained at 0.23 cm s−1 and 6 mA cm−2.