Microbubble-enhanced cold plasma activation for water decontamination: Degradation dynamics and energy yield in relation to pollutant concentration, total volume and flow rate of water

Necessity to safely dispose effluents from industrial wastewater and also water shortage has motivated the search for novel techniques in water treatment. Cold plasma technology is a green, robust, and flexible approach that can sustainably address concerns about removal of pollutants in water. In this study, hydrodynamic cavitation (HC) in a Venturi tube is combined with plasma activated water (PAW) in a continuous system to treat two common antibiotics (sulfathiazole and norfloxacin) and an azo dye (methylene blue). HC increases mass transfer of active species generated from cold plasma discharge from gas to liquid by formation and collapse of cavitation microbubbles. Effects of initial concentration, total volume of circulating water, and water flow rate are studied. Results show that operating at flow rate of 5 L/min and volume of 500 mL for 30 min, all three pollutants with initial concentration of 8 mg/L or lower can be degraded to >80 %. Energy yield and degradation kinetics of experiments are also elaborated. Thus, the setup ameliorates the hurdle of gas - liquid mass transfer. Finally, larger volume samples (2, 10, and 20 L) were treated to show the applicability of the method for more industrial scale levels. Lower concentrated samples degrade faster compared with more concentrated solutions. Besides, a direct relation is shown between water flow rate and degradation signifying the fact that at higher flow rates the amount of reactive species being able to enter the cavitation chamber are greater. The energy yield is estimated to be the highest as the higher initial concentration with short treatment time. Further studies can focus on optimization and extension of the current setup to other chemicals and other gas atmospheres.