Development of low power non-thermal plasma jet and optimization of operational parameters for treating dyes and emerging contaminants

Non-thermal plasma has emerged as an effective treatment system against the latest class of highly recalcitrant and toxic environmental pollutants termed emerging contaminants (ECs). In the present work, a detailed experimental study is carried out to evaluate the efficacy of a non-thermal plasma jet with two dyes, Rd. B and Met. Blue, as model contaminants. The plasma jet provided a complete dye decoloration in 30 min with an applied voltage of 6.5 kV_p−p. ·OH, having the highest oxidation potential, acts as the main reactive species, which with direct action on contaminants also acts indirectly by getting converted into H₂O₂ and O₃. Further, the effect of critical operational parameters viz, sample pH, applied voltage (4.5‒6.5 kV_p−p), conductivity (5‒20 mS cm⁻¹), and sample distance on plasma treatment efficacy was also examined. Out of all the assessed parameters, the applied voltage and sample conductivity was found to be the most significant operating parameters. A high voltage and low conductivity favored the dye decoloration, while the pH effect was not that significant. To understand the influence of plasma discharge gas on treatment efficacy, all the experiments are conducted with argon and helium gases under the fixed geometrical configuration. Both the gases provided a similar dye decoloration efficiency. The DBD plasma system with complete dye removal also rendered maximum mineralization of 73% for Rd. B, and 60% for Met. Blue. Finally, the system's efficiency against the actual ECs (four pharmaceutical compounds, viz, metformin, atenolol, acetaminophen, and ranitidine) and microbial contaminant (E. coli) was also tested. The system showed effectivity in the complete removal of targeted pharmaceuticals and a log2.5 E. coli reduction. The present systematic characterization of dye degradation could be of interest to large communities working towards commercializing plasma treatment systems.