Factors affecting decolourization efficiency of indigo carmine in a coaxial surface plasma falling film reactor

Low temperature plasmas generated in close proximity to water offers a convenient means of generating highly oxidising aqueous phase chemical species capable of degrading recalcitrant organic compounds. To ensure the efficacy of the approach the interplay between the plasma excitation parameters and reactor characteristics must be optimised to facilitate efficient generation and transport of reactive chemical species from the plasma phase to the liquid. In this study, indigo carmine dye was used as a model contaminant to investigate factors affecting degradation efficacy in a coaxial falling film reactor coupled to a surface barrier discharge. Plasma generated species in the gas phase were characterised using Fourier transform infra-red spectroscopy and linked to aqueous phase species in the exposed solution. Parameters including dissipated power, pulse width modulation and reactor sealing conditions were systematically investigated to reveal a maximum decolourisation efficiency of 20.18 g/kWh. Through a comparison with other plasma-based and non-plasma-based advanced oxidation processes it was revealed that the coaxial surface barrier falling film reactor developed in this study is highly competitive and worthy of further investigation.