Degradation of textile dyes in water by gas-liquid NSP-DBD plasma

Textile dyes represent some of the most complicated environmental pollutants due to their variety and complex structure. Cold atmospheric plasma (CAP) is regarded as a highly competitive advanced oxidation process towards the removal of organic pollutants from wastewater. In this study, a gas-liquid nanosecond pulsed dielectric barrier discharge (NSP-DBD) plasma reactor was used for the degradation/mineralization kinetics of three popular dyes (Orange II, Methylene Blue and Methyl Orange). The experimental setup used to treat polluted water samples consisted of a gas-liquid DBD reactor driven by nanosecond pulsed voltage supplied by means of a nanosecond pulse generator producing positive high-voltage pulses of rising time about 4 ns. The applied high voltage pulses and the circuit current were monitored on a digital oscilloscope and measured using a high voltage probe and a current transformer, respectively. The inter-electrode gap was fixed at about 10 mm. The distance between the dielectric surface and aqueous solution surface was about 3 mm and its gap was filled with dry air injected over the aqueous phase at a constant flow rate. We found that the degradation kinetic order is MB>MO>OII. Under the optimized operating window, all dyes are completely degraded at treatment times ranging from 15 to 20 min with the corresponding energy yield being 1.5-2.0 g/kWh.