Treatment of azo, direct, and reactive dyes in surface dielectric barrier discharge: Valorization of effluent, the influence of wastewater characteristics, and plasma modeling by Stark broadening technique

The paper demonstrates the versatility of surface dielectric barrier discharge (SDBD) in degrading brilliant red X3B (azo dye), direct yellow 44 (direct dye), and turquoise blue H5G (reactive dye) in textile wastewater. The influence of wastewater characteristics, such as pH (4-10), background inorganic salts (NaCl, Na2SO4, and Na2CO3), and type of pollutant, on the system performance was studied, and their interactions with center dot OH were established. Using the Stark broadening technique, the electron density of plasma was analyzed (2.48 x 1015/ cm3 at 60 W), demonstrating its suitability for wastewater treatment. Complete degradation of 50 mg/L of brilliant red X3B, direct yellow 44, and turquoise blue H5G was achieved in 24, 32, and 96 min. The corresponding energy yield of 416, 312, and 250 mg/kWh achieved at 60 W indicates the system is energy efficient. Solution pH, background salts, dye type, and molecular size influence degradation efficiency. Alkaline pH enhances reaction rates, while acidic pH reduces reactor performance. Salts such as NaCl, Na2SO4, and Na2CO3 increased degradation time by 1.5-2.0 times due to the scavenging effect. A simple and reliable strategy was employed to recycle the treated effluent and transform it into a calcium nitrate-based liquid fertilizer. The phytotoxicity studies prove that the final effluent is non-toxic to plants and can significantly enhance seeds' germination by 120-140 % compared to tap water-grown seeds. The study established the application of SDBD in wastewater treatment by electron density estimation by the Stark broadening technique and extensive dye degradation and mineralization studies under various environmental conditions.