High-rate photocatalytic degradation of methylene blue by aerated swirl flow vacuum ultraviolet reactor

● About 90% of methylene blue can be removed by VUV within one minute. ● Degradation kinetics by VUV followed a pseudo second-order reaction. ● VUV showed excellent removal even at higher concentrations. ● Transmitting medium highlighted the importance of the quartz sleeve. ● Methylene blue was mineralized by chromophoric and auxochrome degradation. This study aimed to develop a high‑rate and energy efficient process for degrading the recalcitrant dye methylene blue using an aerated swirl flow vacuum ultraviolet (VUV) reactor equipped with xenon excimer lamps. A tangential inlet and corrugated inner wall were used to generate swirl flow around the lamp sleeves, and reactor performance was compared with UVC systems. Flow behavior was characterized by residence time distribution (RTD) and gas-liquid mass transfer was quantified by the volumetric mass transfer coefficient (K La ). The swirl flow VUV reactor showed a narrow and plug‑flow‑like RTD and a higher K La (0.25 s⁻¹) than an ordinary annular reactor (0.05 s⁻¹). Under VUV irradiation, methylene blue degradation reached 90.4% within 1 min. This outperformed UVC (40.0%) by more than 2.3 times. The electrical energy per order (EEO) for VUV reactor was 0.020-0.021 kWh/m³ and 18-4381 times lower than for UVC reactor. With exceptional energy efficiency, VUV decomposed recalcitrant pollutants through a synergistic mechanism of direct photolysis and indirect radical oxidation driven by the generation of ozone and hydroxyl radicals. The key oxidants generated in the aerated swirl flow VUV reactor were 1.0 × 10 -13 M (∙OH), 2.0 × 10 -5 M (O 3 ), and 1.0 × 10 -15 M (O( 1 D)). The aerated swirl flow VUV system provided a superior, scalable, and energy efficient approach for the treatment of recalcitrant organic dyes and showed strong potential for full‑scale application in water treatment processes.