Electrical discharge treatments of synthetic dyeing wastewater were carried out with two different systems: underwater pulsed electrical discharge (UPED) and underwater dielectric barrier discharge (UDBD). Reactive Blue 4 (RB4) and Acid Red 4 (AR4) were used as model contaminants for the synthetic wastewater. The performance of the aforementioned systems was compared with respect to the chromaticity removal and the energy requirement. The results showed that the present electrical discharge systems were very effective for degradation of the dyes. The dependences of the dye degradation rate on treatment time, initial dye concentration, electrical energy, and the type of working gas including air, O2, and N2 were examined. The change in the initial dye concentration did not largely affect the degradation of either RB4 or AR4. The energy delivered to the UPED system was only partially utilized for generating reactive species capable of degrading the dyes, leading to higher energy requirement than the UDBD system. Among the working gases, the best performance was observed with O2. As the degradation proceeded, the concentration of total dissolved solids and the solution conductivity kept increasing while pH showed a decreasing trend, revealing that the dyes were effectively mineralized.

Non‐thermal plasma combined with photocatalysis is a viable technique for the degradation of organic impurities in wastewater. In this work, a specially devised dielectric barrier discharge plasma reactor system coupled with photocatalysis was applied to the degradation of CI Acid Red 4 which is commonly used as a textile dye. Dye degradation in the combined system was evaluated with three different photocatalysts: titanium oxide, zinc oxide, and graphene oxide. The photocatalysts were characterised by X‐ray diffraction, particle size analysis, and Brunauer–Emmett–Teller specific surface area. It was found that the combination of photocatalysis with plasma substantially improved dye degradation by comparison with plasma alone. To identify which photocatalyst exhibited the best performance, the influence of photocatalysis alone on dye degradation was separately determined using an ultraviolet lamp, which showed that graphene oxide, which has a broad band gap, degraded the dye most effectively.

The inactivation of Escherichia coli was investigated with two types of underwater electrical discharge systems such as pulsed electrical discharge (PED) and dielectric barrier discharge (DBD). The DBD system consisted of a quartz tube and a coaxial discharging electrode, which was submerged in biologically contaminated water. In the underwater PED system, the electrical discharge starting from the tip of submerged tubular discharging electrode propagated downward and the direction of working gas injected through the discharging electrode was also downward. The inactivation performances of the underwater electrical discharge systems were comparatively examined with experimental variables including working gas type, the mode of operation, electrical energy and treatment time. With air or oxygen as a working gas, the DBD system showed much better inactivation performance than the PED system, but with nitrogen the PED system was superior, suggesting that these two types of underwater electrical discharge systems are different in dominant inactivation mechanisms. The inactivation by the DBD could be best characterized by the ozonation, and the contribution of the UV irradiation was minor. An operation at lower electric power (the DBD case) or at lower pulse repetition rate (the PED case) consumed less electrical energy for the inactivation, but it required longer inactivation time.

This work investigated the hydrophobic coating of silicate yellow phosphor powder in the form of divalent europium-activated strontium orthosilicate (Sr2SiO4:Eu 2+ ) by using an atmospheric pressure dielectric barrier discharge (DBD) plasma with argon as a carrier and hexamethyldisiloxane (HMDSO), toluene and n-hexane as precursors. After the plasma treatment of the phosphor powder, the lattice structure of orthosilicate was not altered, as confirmed by an X-ray diffractometer. The coated phosphor powder was characterized by scanning electron microscopy, fluorescence spectrophotometry and contact angle analysis (CAA). The CAA of the phosphor powder coated with the HMDSO precursor revealed that the water contact angle increased from 21.3° to 139.5° (max. 148.7°) and the glycerol contact angle from 55° to 143.5° (max. 145.3°) as a result of the hydrophobic coating, which indicated that hydrophobic layers were successfully formed on the phosphor powder surfaces. Further surface characterizations were performed by Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry, which also evidenced the formation of hydrophobic coating layers. The phosphor coated with HMDSO exhibited a photoluminescence (PL) enhancement, but the use of toluene or n-hexane somewhat decreased the PL intensity. The results of this work suggest that the DBD plasma may be a viable method for the preparation of hydrophobic coating layer on phosphor powder.