Hybrid water treatment flow plant using hydrogen peroxide-based electro-activated persulfate and photoelectro-Fenton processes: The combustion of Reactive Orange 16 dye

Abstract

This paper implements an innovative hybrid water treatment process in a flow plant using hydrogen peroxide-based electro-activated persulfate (EPS-H2O2) combined with photoelectro-Fenton (PEF) method. The Reactive Orange 16 (RO16) azo dye was used as a persistent organic pollutant (POP) model. A filter-press reactor utilized a Ti|RuO2 plate and a gas diffusion electrode (GDE) as the anode and cathode. In EPS-H2O2, persulfate (PS) reacts with H2O2 yielding hydroxyl (•OH) and sulfate (SO4·-) radicals. In PEF, H2O2 reacts with Fe2+ producing more •OH, completing the TOC removal in the presence of UVA light. The influence of pH (3–9), initial PS concentration (0.5–1.5 mM), initial RO16 dye content (30–50 mg L-1 TOC), applied current density (j, 5–30 mA cm−2), and mean linear flow velocity (u, 7.3–29.1 cm s−1) on the EPS-H2O2 process efficiency was examined. The best trial for EPS-H2O2 achieved 37% TOC removal in 360 min electrolysis at j = 10 mA cm−1, u = 14.6 cm s−1, and PGDE = 3 psi. Subsequently, at t ≥ 360 min, the synergistic effect between the EPS-H2O2 and PEF processes was carried out by adding 0.5 mM Fe2+ and UVA light. The best hybrid (EPS-H2O2 + PEF) process test reached 98% mineralization with 30% current efficiency and 0.060 kWh (g TOC)-1 electrolytic energy consumption. Six carboxylic acids were determined as the main intermediaries, whereas ammonium was the main nitrogen compound throughout the EPS-H2O2 and PEF processes.