Effect of Persulfate on the Degradation of Acid Orange 7 (AO7) by Dielectric Barrier Discharge Plasma

A novel process for decolorization of Acid Orange 7 (AO7) dye wastewater by dielectric barrier discharge plasma coupled with persulfate (PS) was investigated, and the enhancing performance of PS on the AO7 decolorization efficiency and energy efficiency were examined under different molar ratio of AO7 to PS (MR), gas discharge gap, initial concentration of AO7 and gas discharge atmosphere. The experimental results indicate that the decolorization efficiency (ƞ) and the energy efficiency (γ) increased with the addition dosage of PS until the MR of 1:100, and an increment in the decolorization efficiency and energy efficiency reached 60.5% and 0.33 g/(kW h) respectively at an MR of 1:100. An increase in the gas discharge gap and in the initial concentration of AO7 greatly decreased the decolorization efficiency of AO7, but the increment in energy efficiency due to PS addition increased with the AO7 initial concentration and discharge gap except for the discharge gap of 8 mm, and the highest increment in energy efficiency of 0.75 g/(kW h) was obtained at a gas discharge gap of 6 mm and an initial concentration of 30 mg/L. Moreover, higher AO7 decolorization efficiency was achieved in air than in Ar atmosphere, while the increment in decolorization efficiency and energy efficiency due to PS addition was not influenced by the gas discharge atmosphere. The experimental results imply that PS was activated into stronger radical species such as sulfate radical and hydroxyl radical, which contributed to a higher decolorization performance. The possible motivator of PS was tentatively concluded as UV irradiation, Joule heating effect, etc.