Treatment of textile dyes in a photo-surface dielectric barrier discharge hybrid reactor: Unraveling the degradation mechanisms.

The study demonstrates the unprecedented ability of UV-C integrated surface dielectric barrier discharge (photo-SDBD) in the rapid removal of azo (brilliant red X3B), direct (direct yellow - 44), and reactive dyes (turquoise blue H5G) in textile wastewater. The degradation mechanisms of these dyes were studied using a high-resolution mass spectrometer (HRMS), and a step-by-step reaction pathway was proposed. The BR-X3B and DY-44 dyes undergo azo bond dissociation followed by functional group rearrangement, ring opening, and formation of open chain intermediates. On the other hand, TB-H5G underwent dissociation of porphyrin moieties, side chain cleavage, and aromatic ring cleavage, generating open-chain intermediates. The photo-SDBD showed a superior ability to degrade the dyes compared to SDBD over a pH range of 4-10 and a background salt concentration of 10,000 mg L-1. Salt presence did not significantly affect the photo-SDBD performance, irrespective of the dye and salt types used. The photo-SDBD showed a 2.4-6.5 times higher degradation rate and 1.4-2.9 times higher energy yield than SDBD. The hybrid system took only 42-84 min to mineralize dyes (>99%) depending upon the complexity of the molecule, whereas SDBD required double the time than photo-SDBD. The study proves that photo-SDBD is more energy-efficient and versatile than SDBD. Moreover, the hybrid system is less susceptible to wastewater characteristics such as pH and inorganic salts, making it a potential alternative to conventional plasma and other advanced oxidation processes for treating textile wastewater.