Comprehensive analysis of experimental conditions in plasma–liquid interaction for the efficient removal of methylene blue

Abstract

A comprehensive investigation of the input parameters in a plasma–liquid interaction (PLI) for the removal of methylene blue (MB) in artificial wastewater was conducted using a cold atmospheric pressure Ar plasma jet (jet temperature ≤ 40 °C). The Ar plasma jet was generated by a gliding arc configuration and driven with a 50 Hz AC high voltage. The effects of key parameters on MB removal efficiency were systematically examined, including stirring solution, distance from the plasma jet source to the liquid surface, interaction time, initial MB concentration, and Ar flow rate. These results indicate that increasing the Ar flow rate, treatment time, and stirring solution improved the MB removal efficiency. In contrast, the efficiency decreased with distance and the initial MB solution. To evaluate the magnitude of these factors, a quadratic equation was developed to predict MB removal efficiency, demonstrating good agreement with the experimental data. Consequently, the relative importance of the factors based on first-order coefficients was determined as follows: treatment time > Ar flow rate > initial MB concentration > distance > stirring solution. These findings provide valuable insights for optimizing the plasma configuration and operating conditions for efficient MB removal via PLI treatment. Remarkably, 99% of MB degradation in the feed (20 mg L⁻¹) was achieved within 50 minutes of treatment, with an energy efficiency of 82.76 mg MB per kW per h, corresponding to 241.67 kW h m⁻³ for an initial MB of 20 mg L⁻¹. This process is environmentally friendly owing to its low electrical energy consumption and the fact that no chemicals are used.