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

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 ( u r ) and the co-existing ions on the fluoride and arsenic removal efficiencies was analyzed. All EC tests, performed at 0.23 ≤  u r  ≤ 0.93 cm s −1 and 5 ≤  j  ≤ 7 mA cm −2 , satisfied the World Health Organization (WHO) standard for fluoride ( C F - ≤ 1.5 mg L −1 ). The EC tests that satisfied the WHO standard for arsenic ( C As  ≤ 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 .