Continuous electrocoagulation-flocculation-sedimentation process to remove arsenic, fluoride, and hydrated silica from drinking water

Abstract

The novelty of this paper lies in the novel design and experimental characterization of a laboratory-scale electrocoagulation-flocculation-sedimentation flow plant to remove arsenic (As), fluoride ($F^{-}$) and hydrated silica (SiO₂) from natural deep well water (31.50 μg L⁻¹ As, 1.12 mg L⁻¹ $F^{-}$, 80 mg L⁻¹ SiO₂, 0.31 mg L⁻¹ ${\mathrm{PO}}_4^{3-}$, 15 mg L⁻¹ ${\mathrm{SO}}_4^{2-}$, 141 mg L⁻¹ alkalinity, 124.30 mg L⁻¹ hardness, pH 8 and 572 μS cm⁻¹ conductivity). The electrocoagulation reactor includes AlFe hybrid plate electrodes as sacrificial anodes. A laboratory-level flocculation-settler equipment is connected in series with the electrocoagulation reactor. The influence of the mean linear flow velocity (1.31 < u < 5.26 cm s⁻¹) and current density (3 < j < 5 mA cm⁻²) in the electrolyzer on the removal of As, $F^{-}$, and SiO₂ was examined, finding the best experimental condition at j = 5 mA cm⁻² and u = 1.31 cm s⁻¹, with an operational cost of OC = 0.41 USD m⁻³. The As, $F^{-}$, and SiO₂ removal percentages were 100, 82.80, and 98.60 %, respectively. The spectroscopic analysis (SEM-EDS, XRF-EDS, XRD, and FTIR) revealed the formation of sodium and calcium aluminosilicates and iron oxyhydroxides as flocs. The continuous process proved here envisages a promising deep well water decontamination future.