Treatment of azo dye (Acid Orange II) wastewater by pulsed high-voltage hybrid gas-liquid discharge

Pulsed high-voltage electrical discharge was used in treating azo dye (Acid Orange ii, AO7) wastewater. The effects of initial pH, Fe²⁺ concentration, discharge mode, conductivity of initial aqueous solution and the type of bubbling gas (air, O₂, N₂) on AO7 degradation were studied. A new gas-liquid discharge (NGL) mode, by which a plate was exposed to air and needles were immersed in liquid, displayed a remarkably better AO7 degradation than the gas-liquid discharge (GL) mode and the liquid discharge (L) mode. The lower conductivity of aqueous solution and the higher oxygen concentration in bubbled gas were of benefit to the degradation process. In addition, owing to the multi-point structure and self-provided Fe²⁺, the electrode with iron mesh-plate discharge showed a more competitive degradation performance than that with multi-needle-plate discharge. The oxidant of OH and H₂O₂ induced by the discharge process were also studied to explore the degradation processes. By NGL mode with iron mesh electrode and bubbled air in reactor, the degradation efficiency of AO7 was up to 85.8% when the initial pH, conductivity and Fe²⁺ concentration were 2.28, 200 μS·cm^-1 and 1.635 mmol L^-1, respectively.