Degradation of various textile dyes as wastewater pollutants under dielectric barrier discharge plasma treatment

Textile dyes represent some of the most complicated environmental pollutants due to their variety and complex structure. Plasma oxidation methods have emerged as viable techniques for effective decomposition of these pollutants. We examined the degradation of a wide variety (13 overall) of industrial textile dyes in a pilot dielectric barrier discharge (DBD) semi-continuously operated plasma reactor. Plasma was generated in a quartz tube with central liquid-filled electrode immersed in wastewater; ambient air was used as a feeding gas for the reactor. The performance of the reactor was evaluated based on the production of ozone (gas and liquid phase). The kinetics and by-products of the oxidation process were determined by UV/VIS spectrophotometry, FTIR analysis and toxicity tests. The yield of ozone production ranged between 0.19 mg/s and 0.46 mg/s by varying the discharge power between 3 and 33 W. The demand of energy to decompose separate dyes ranged from 18.7 to 866 kJ/g. 10 of 13 dyes were decomposed up to 95% during 300 s of reactor operation. The FTIR analysis revealed that degradation by-products consisted mostly of carboxylic acids, nitrates, amides and amines. The treatment process was found to decrease the toxicity of the wastewater to near-zero values. Low energy consumption and short decolorization time suggested that DBD plasma method may be competitive technology for primary decomposition of hardly degradable textile dyes in wastewater.