Electro activation of persulfate using iron sheet as low-cost electrode: the role of the operating conditions

This work assesses the role of the operational conditions upon the electro-activation of persulfate (PS) using sacrificed iron electrode as a continuous low-cost Fe²⁺ source. An aqueous phenol solution (100 mg L^-1) was selected as model effluent. The studied variables include current density (1-10 mA cm^-2), persulfate concentration (0.7-2.85 g L^-1), temperature (30-90°C) and the solution conductivity (2.7-20.7 mS cm^-1) using Na₂SO₄ and NaCl as supporting electrolyte. A mineralization degree of around 80% with Na₂SO₄ and 92% in presence of NaCl was achieved at 30°C using 2.15 g L^-1 PS at the lowest current density tested (1 mA cm^-2). Besides PS concentration, temperature was the main variable affecting the process. In the range of 30-70°C, it showed a positive effect, achieving TOC conversion above 95% (using Na₂SO₄ under the previous conditions) along with a significant increase in iron sludge, which adversely affects the economy of the process. A lumped and simplified kinetic model based on persulfate consumption and TOC mineralization is suggested. The activation energy obtained for the TOC decay was 29 kJ mol^-1. An estimated operating cost of US$ 3.00 per m³ was obtained, demonstrating the economic feasibility of this process.