## 3 Results and Discussion
### Effects of the UV Light Source and TiO\({}_{2}\) Photocatalysis on Inactivation of Microorganisms  
The initial population of _E. coli_ K12 and _S. cerevisiae_ were 6.9 log CFU/mL and 5.3 log CFU/mL, respectively. For _E. coli_ K12, VUV treatment showed a slightly higher inactivation effect than UVC (Figure 5a). For the first 30 s, UVC-TiO\({}_{2}\) and VUV-TiO\({}_{2}\) resulted in bacterial reductions of 0.9 log and 1.5 log CFU/mL, respectively, which were slightly lower than for UVC and VUV alone. After 120 s of treatment, UVC-TiO\({}_{2}\) and VUV-TiO\({}_{2}\) resulted in bacterial inactivation of 4.0 log and 3.9 log CFU/mL, respectively, which were slightly higher than for UVC and VUV alone. Figure 4: Effects of air bubble induced agitation on the pesticide degradation efficiency under VUV-assisted TiO\({}_{2}\) photocatalytic treatment (VUV-TiO\({}_{2}\)). (**a**) pyraclostrobin; (**b**) boscalid; (**c**) fluidoxonil; and (**d**) azoxystrobin. A cocktail solution was composed of individual pesticides at 5 ppm (_w/v_). No aeration = magnetic stirring at 300 rpm; mild aeration = air flow rate of 1.8 L/min with magnetic stirring at 300 rpm; and, extra aeration = air flow rate of 20 L/min with magnetic stirring at 300 rpm. Results represent the mean of three measurements \(\pm\) standard deviation. For _S. cerevisiae_, UVC, VUV, UVC-TiO\({}_{2}\), and VUV-TiO\({}_{2}\) showed similar inactivation effects of 0.2\(-\)0.4 log, 0.6\(-\)0.8 log, 1.2\(-\)1.3 log, and 1.9\(-\)2.0 log CFU/mL for 30, 60, 90, and 120 s, respectively (Figure 5b). In this study, UVC, VUV, UVC-TiO\({}_{2}\), and VUV-TiO\({}_{2}\) provided similar inactivation effects against microorganisms in aqueous medium. It was estimated that UV light at 254 nm, which was used in all treatment conditions (UVC, VUV, UVC-TiO\({}_{2}\), and VUV-TiO\({}_{2}\)), was a key factor for microbial inactivation. UVC spectrum, especially at 250-270 nm, is the most lethal wavelength range for microorganisms due to strong absorption by nucleic acids. The UV-induced damage to the DNA and RNA of a microorganism is due to the dimerization of pyrimidine molecules. In particular, when thymine (found only in DNA) is dimerized, it becomes difficult to replicate nucleic acids and, even if replication occurs, it often produces a defect that interferes with the survival of microorganisms [51]. In addition, the advantage of the TiO\({}_{2}\) photocatalytic reaction that overcomes the shadow effect, the limitation of UV irradiation, may not be clearly revealed in a short time for microorganisms in a transparent aqueous solution. Further investigation is needed to uncover any reactive difference between photolysis and TiO\({}_{2}\) photocatalysis. It can be achieved using UV irradiation, such as UVB or UVA, not to give serious damage to nucleic acids. However, because the objective of this study was to investigate the potential of photolysis and TiO\({}_{2}\) photocatalysis for simultaneous degradation of pesticides and microorganisms, VUV, and UVC spectrum with energetic photon, which is effective for the degradation of chemical compounds were chosen as a light source. In this study, Gram-negative _E. coli_ K12 showed less resistance to the TiO\({}_{2}\) photocatalytic treatments (UVC-TiO\({}_{2}\) and VUV-TiO\({}_{2}\)) than yeast _S. cerevisiae_. Previous studies attributed this behavior to distinctive interactions of _E. coli_ with TiO\({}_{2}\) surfaces [52; 53; 54; 55]. Another study proposed that cell wall structures in microorganisms are responsible for different sensitivities towards TiO\({}_{2}\) photocatalysis and UV treatment [56]. Another study suggested that the susceptibility of microorganisms to reactive oxygen species can be generally arranged in the following descending order: viruses \(>\) prions \(>\) Gram-negative bacteria \(>\) Gram-positive bacteria \(>\) yeasts \(>\) molds [57]. Figure 5: Effects of the UV light source and TiO\({}_{2}\) photocatalytic on inactivation of microorganisms in aqueous media. (**a**) _E.