Abstract
Nonthermal-plasma (NTP) serves a promising water disinfection technology that inactivates microorganisms under more mild conditions while meeting microbial safety standards and preserving bioactive compounds essential to drinking water quality and composition. Compared with ultraviolet radiation and other disinfection methods, plasma disinfection is more convenient, practical, and safer, with low consumption of chemicals, environmental protection, and a wide range of applications. Utilizing high voltage power in contact with liquid to produce a plasma discharge reaction from non-thermal plasma has been shown to microbicidal and promising in industrial applications. In this study, a novel, continuous liquid-phase plasma discharge (CLPD) process that shows promise for microbial inactivation was developed and evaluated. The reactor design enables the generation of a stable plasma discharge in a continuous operation to improve the treatment efficiency by producing reactive chemical species. This research included the establishment of the CLPD treatment system, identification, screening, and optimization of the significant operational parameters to determine the optimal treatment conditions, and exploration of the inactivation mechanism of an exemplar microbial strain, Escherichia coli (E. coli), by the novel CLPD process. Inactivation of microorganisms in water as was investigated while focusing on the bactericidal activity and its persistence in water. CLPD reduced the concentration of E. coli by 1.2-7.2 logs. The E. coli inactivation efficiency depends significantly on the liquid flow rate of the CLPD system and the applied power. The lowest energy consumption for 6 log E. coli reduction was achieved by applying 250 Watts power with a water flow rate of 52.3 mL/min. Scanning electron microscopy results confirmed that the CLPD treatment process would damage the bacterial cell wall. In addition, it was proved that the inactivation of E. coli was mainly attributed to the oxidation induced by reactive oxygen species. In addition, the electrical conductivity, pH, and other chemical properties of the water treated with CLPD did not change significantly.