Tetracycline degradation by nonthermal plasma: removal efficiency, degradation pathway, and toxicity evaluation

Tetracyclines (TCs) are often discussed as one of the emerging contaminants detected in water matrices and studied for their persistence towards conventional water treatment technologies. In this work, the treatment of TC in aqueous solutions with nonthermal plasma gliding arc process was investigated. The degradation efficiency of TC was studied along with the effect of initial concentration, working gas, pH, and the presence of a radical scavenger. The generation of reactive oxidative species was characterized by the quantification of radical hydroxyl, hydrogen peroxide, ozone, nitrite, and nitrate. Mineralization efficiency was examined by assessment of Total organic carbon evolution. Experimental results have shown that the gliding arc plasma is effective for the treatment of TC. At an initial concentration of 5 mg/L: degradation rates of 94.95% and 60.45% were achieved, while mineralization rates were 81.3% and 57.34% under O₂ and air plasma, respectively. O₂ plasma exhibited an immense potential for the generation of reactive oxygen species. Meanwhile, air plasma showed better degradation performance in the presence of a radical scavenger. Moreover, degradation products were identified by mass spectroscopy analysis and degradation pathway was proposed. The gliding arc process proposed in this work is promising for the removal of TC antibiotics.