Efficient degradation and mineralization of methylene blue via continuous-flow electrohydraulic plasma discharge

Abstract

A continuous-flow electrohydraulic plasma discharge (EHPD) process characteristic of establishing a stable discharge through the conducting channel of in the center orifice of a dielectric plate was developed and investigated to degrade methylene blue (MB) in water. The effect of three operating parameters, i.e., liquid flow rate (37−94 ml/min), air flow rate (1−4 L/min), and initial dye concentration (10−100 mg/L), on the MB degradation efficiency was evaluated. The results indicated that a complete degradation of MB was achieved within 10 min of treatment for all MB concentrations tested. The optimum liquid and air flow rates were 68 mL/min and 3 L/min, respectively, for the process to remove MB in a circular flow operation. The energy efficiency for different operating parameters was in the range of between 0.16 g/kWh and 0.81 g/kWh at 50% conversion. Reaction kinetics and the possible MB degradation pathway was analyzed and proposed. Hydroxyl radicals were found to be the dominant reactive species responsible for the MB degradation. Mineralization of MB was demonstrated by a 92.5% COD removal within10 min treatment for an initial MB concentration of 100 mg/L. The overall results indicated that the novel, continuous-flow EHPD reactor is a robust and highly effective process for degradation and mineralization of MB, a potential technology that can overcome the limitations of advanced oxidation processes for wastewater treatment.