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In this study, a microbubble‐enabled plasma reactor driven by a nanosecond‐pulsed generator was developed to provide an effective means for transferring highly reactive plasma species into liquids for plasma‐activated water (PAW) production. The physicochemical characteristics of PAW at different temperatures were evaluated, and the corresponding antimicrobial effects of PAW against Escherichia coli cells were investigated. Results show that the microbubble‐enabled PAW at a lower temperature (10°C) had the highest antimicrobial activity, resulting in a 2.43 ± 1.02‐log10 reduction of E. coli in PAW. The excellent energy efficiency of the total reactive oxygen and nitrogen species production in PAW is 10.37 g kW−1 h−1. Overall, this study provides much‐needed insights into the microbubble‐enabled plasma chemistries for optimizing the biochemical activity of PAW. [ABSTRACT FROM AUTHOR]

The chemistry, antimicrobial efficacy and energy consumption of plasma-activated water (PAW) was optimized by altering the discharge frequency, ground-electrode configuration, gas flow rate and initial water conductivity for two reactor configurations, i.e., air pin-to-liquid discharge and air plasma-bubble discharge in water. The ratio of NO 2 − and NO 3 − formation was altered to optimise the antimicrobial effects of PAW, tested against two Gram-negative bacteria. An initial solution conductivity of 0.2 S·m−1 and 2000-Hz discharge frequency with the ground electrode positioned inside the pin reactor showed the highest antimicrobial effect resulting in a 3.99 ± 0.13-log 10 reduction within 300 s against Escherichia coli and 5.90 ± 0.24-log 10 reduction within 240 s for Salmonella Typhimurium. An excellent energy efficiency of reactive oxygen and nitrogen species (RONS) generation of 10.1 ± 0.1 g·kW−1·h−1 was achieved. Plasma-activated water (PAW) is deemed as an eco-friendly alternative to chemical disinfection because its bactericidal activity is temporary. Optimizing the design and operation of PAW reactors to achieve high inactivation rates of more than 5-log 10 reductions, as demonstrated in this work, will support the industrial application of this technology and the scaleup at industrial level. • Increasing discharge frequency from 1000 to 2000 Hz improved the antimicrobial characteristics of PAW by the pinreactor • Increasing initial liquid conductivity in the pin reactor increased the bacterial inactivation to 1.74–4.4-log 10 reduction • Ground electrode inside the pin reactor caused higher E. coli (3.99-) and S. Typhimurium (5.90-log 10 reduction) inactivations • Altering ground-electrode position from inside to outside the bubble reactor changed the NO 2 −/ NO 3 − ratio from 0.92 to 2.69 • The optimal PAW configuration, achieving more than 5-log reduction of S. Typhimurium , was the pin-to-liquid discharge [ABSTRACT FROM AUTHOR]