Treatment of brilliant blue by plasma and combination plasma with photocatalysis process intensification

Various treatment methods are widely used to reduce water pollution. Among these techniques, heterogeneous photocatalysis and non-thermal plasma technologies, notably dielectric barrier discharges, are currently the most suitable for water treatment. However, the use of each of these processes alone presents certain limitations. In this study, the brilliant blue (BB) photo-degradation was investigated via the dielectric barrier discharge (DBD) method. The impact of certain process factors, including the model pollutant’s initial concentration (from 5 to 10 mg/L), the airflow rate (240 L/h) as well as the frequency (from 230 to 400 Hz), upon the DBD’s performance in terms of bright blue decomposition and mineralisation was assessed. The latter reached 49.5% for 120 minutes, assuming optimised operating parameters (BB initial concentration of 10 mg/L, airflow rated at 240 L/h, 21 kV as an applied voltage at 400 Hz). It could be said that DBD processing has a high ecological potential for the aqueous degradation of BB. Scavenger analysis indicated that the radicals O2−°, HO2°, as well as °OH, represent the underlying oxygen reactive species in the process of brilliant blue decomposition. The study showed that both reactive nitrogen species and ROS contribute to the process of BB removal. For approximating real-life requirements, DBD tests were performed in both tap and synthetic water matrices. The degradation and mineralisation of BBs were significantly inhibited in tap water (% Degradation = 71.3, % Mineralisation = 31.6) and synthetic water (% Degradation = 65.41, % Mineralisation = 12), compared to BB degradation and mineralisation in ultrapure water (% Degradation ≥ 98, % Mineralisation = 49.5), after 120 min of irradiation. This proved that inorganic and organic molecules in tap and synthetic water reduce BB degradation efficiency. Thus, our pollutant was treated by the combination plasma-photocatalysis system using cellulose paper-supported titanium dioxide as a photocatalyst, which showed a significant improvement in BB decomposition efficiency versus considering either separate process.