Feasibility of surface dielectric barrier discharge in wastewater treatment: Spectroscopic modeling, diagnostic, and dye mineralization

Abstract

The paper investigates the ability of a surface dielectric barrier discharge (SDBD) based reactor to mineralize complex organic molecules such as azo dyes in water. The high operational flexibility, low maintenance, and energy efficiency of SDBD over most of the other plasma systems motivated its selection. Also, SDBD produces even discharge over a relatively large surface area. This could enhance plasma-liquid interaction and the production of reactive chemical species. Optical emission spectroscopy coupled with the collision radiative model and temperature measurements reveals the non-equilibrium nature of the plasma. Through plasma diagnostics, the study established the ability of SDBD to generate high energetic electrons with an electron temperature of 1.6 eV at a moderate sample temperature. The data supports the effective generation of reactive chemical species by SDBD reactor and its suitability for wastewater treatment with less energy consumption. The enhanced ability of the SDBD to mineralize azo dye (Brilliant Red 5B) in water is demonstrated under ambient conditions. The reactor is operated as a function of initial dye concentration, pH, and background salts such as NaCl, Na2SO4, and Na2CO3 to understand their effect on dye degradation. Faster degradation and mineralization of Brilliant Red 5B were observed due to the enhanced generation of •OH and H2O2 in the liquid medium. The degradation and complete mineralization of 50 mg/L of dye was achieved at hydraulic retention times of 20 min and 72 min, respectively. Compared to other plasma reactors reported, the present system showed a high energy yield of 247 mg/kWh at an operating power of 60 W and initial dye concentration of 50 mg/L. In short, the studies address two significant challenges of using plasma in wastewater treatment, i.e., energy efficiency and scalability.