Enhancement of Tunisian groundwater treatment through the simultaneous removal of sulfate, nitrate and nitrogen by-products using a hybrid electrochemical process

Abstract

Combined electrocoagulation (EC) and electrooxidation (EO) process was applied to increase Tunisia's drinking water potential from a highly sulfate and nitrate contaminated groundwater. Firstly, batch EC experiments were carried out using Al electrodes under current density (7.2 to 59.5 mA cm⁻²), initial pH (3.0 to 11.0), and temperature (10.0 to 50.0 °C). The results showed that high removal efficiencies, 83.2 % and 82.1 % for sulfate and nitrate, respectively, were achieved at 42.8 mA cm⁻², initial pH 7.0, and 30.0 °C, while excessive amounts of 0.4 mg NO₂⁻_N L⁻¹ and 11.6 mg NH₄⁺_N L⁻¹ were produced. The mechanism study revealed that, at ambient temperature (20–30 °C), sulfate removal by adsorption on Al hydroxides was dependent of generated amount of hydroxide anions resulting from nitrate reduction into nitrogen by-products on the cathode. In second step, EO using a novel electrodes' combination (Ti/RuO₂ anode and Ti cathode), under current density (7.5 to 30.0 mA cm⁻²), initial pH (8.5, 10.0), and initial temperature (10.0 to 50.0 °C), was implemented. The optimized conditions were found at 15.0 mA cm⁻², initial pH 8.5, and 20.0 °C, leading to complete removal of NO₂⁻ and NH₄⁺ in the form of N₂ in <20 min.