Continuous flow wastewater induced plasma microbubbles for the enhancement of mass transfer and degradation of dye pollutants in a bubble column reactor

Abstract

To enhance the mass transfer and organic pollutants oxidation in the plasma bubble column reactor (BCR), a Venturi tube was utilized to produce flowing wastewater containing plasma microbubbles by hydrodynamic cavitation (HC) effect. Meanwhile, the convection of wastewater was optimized through adjusting Reynolds number at the throat of the Venturi tube (Re_T: 5870 – 56,300). The variation of C_v and ΔP with the Re_T revealed the starting point of the HC at the Re_T of 24,600 (210 L·h^-1). The HC effect reduced the minimum plasma bubble size d to 100 μm and increased the gas holdup of plasma bubbles (11 %). Comparing the plasma bubbling mode without liquid flow, energy yield (EY) of plasma degradation (2333 mg·kWh^-1 at the removal of 90 %) and the volumetric mass transfer coefficient (k_la = 0.037 s^-1) was improved by 1.63 and 3.08 times, respectively. The dimensionless mass transfer correlation among Reynolds number Re (220 – 2113), Froude number Fr (0.0019 – 0.0075), initial concentration difference (c₀/c₅₀: 0.5 – 2.0), and Sherwood number Sh in the HC-BCR have been established. This study provides insights to optimize the convection of wastewater in the HC channel for the enhancement of plasma oxidation in the BCR.